NCICT Project of NAITA

ACKNOWLEDGEMENTSI have grate pleasure in expressing my heartiest thanks to the who have helped me submit this project first and fore most I would like acknowledgements with pleasure Mr.S.Seelan, Computer Co-ordinator and lecture in NAITA. I am grateful to Mr.S.Pavalanathan, present NAITA chairmen who also help me. I have to also personally thankful to Mr.S.Seelan, lecture NAITA Computer Training Center and supervisor for this project report for valuable ideas, recommendations and supports, he whice have added quality to this project. I am also especially thank our public library in Vavuniya and I take this opportunity offering my grateful thank to all my friends and colleagues and my family members who have been grate help to me personally prepare this project. Once again I thank to you all. ............................................ (A.KOGULAN) CONTENTS Chapters Chapter 01 Introduction to computer What is Information Technology? Father of computer Computer or a pc Computers in human lives A complete computer system Age of computers Classification of Computers The Five Generations of Computers Computer Generations briefly Explanation Artificial intelligence Main Circuit Board of a PC History of the Motherboard Programming Languages Intel Processors: Now and Then 001 002 004 005 007 009 010 012 018 021 029 030 036 040 044 Page Chapter 02 The Components of a Computer Input Devices Output Devices CPU (Central Processing Unit) How computers work? Booting Process Operating system 053 058 069 076 079 080 082 Chapter 03 System Software Application Software 090 095 Chapter 04 Introduction to Computer Viruses Installing Anti-virus Software 099 110 Chapter 05 Primary Storage Secondary Storage 122 128 Chapter 06 Networks Internet & WWW The Number Systems Characters and decimal, binary, ASCII, EBCDIC Value Capital Letters Small Letters Shortcut Keys What is DOS? DOS commands and explanation Modem error messages Abbreviation 220 221 222 226 228 232 240 137 172 217 INTRODUCTION TO COMPUTER We might be aware of the fact that the computer is affecting our lives in many ways. Almost everyday we hear about the newest ways that a computer is being used for. So why not to Call it a Computer Revolution. Computers have now become an important part of our lives with all these rapid development taking place. Till now you might have been using a typewriter for drafting your commercial correspondence a calculator for performing lengthy calculations and files for maintaining records. Now we can do all our correspondence, calculation and record main fence on a computer at a much faster speed. Besides facilitating the office work. Computers today are also paying a significant role in the fields of education and entertainment. As the use of computers steadily increases, so does the need for batter understanding of its functions. WHAT IS INFORMATION TECHNOLOGY? IT (information technology) is a term that encompasses all forms of technology used to create, store, exchange, and use information in its various forms (business data, voice conversations, still images, motion pictures, multimedia presentations, and other forms, including those not yet conceived). It's a convenient term for including both telephony and computer technology in the same word. It is the technology that is driving what has often been called "the information revolution." Data and Information Data is a collection of raw unprocessed facts, figures, and symbols. Computers process data to create information. Information is data that is organized, meaningful, and useful. Computer processes several data items to produce a paycheck. Another example of information is a grade report, which is generated from data items such as a student name, course names, and course grades. A user is someone who communicates with a computer or uses the information it generates. Hardware is the electric, electronic, and mechanical equipment that makes up a computer. Software is the series of instructions that tells the hardware how to per form tasks. Without software, most hardware is useless. The hardware needs instructions from software to process data into information. Data (1) In computing, data is information that has been translated into a form that is more convenient to move or process. Relative to today's computers and transmission media, data is information converted into binary digital form. (2) In computer component interconnection and network communication, data is often distinguished from "control information," "control bits," and similar terms to identify the main content of a transmission unit. (3) In telecommunications, data sometimes means digital-encoded information to distinguish it from analog-encoded information such as conventional telephone voice calls. In general, "analog" or voice transmission requires a dedicated continual connection for the duration of a related series of transmissions. Data transmission can often be sent with intermittent connections in packets that arrive in piecemeal fashion. (4) Generally and in science, data is a gathered body of facts. Some authorities and publishers, cognizant of the word's Latin origin and as the plural form of "datum," use plural verb forms with "data". Others take the view that since "datum" is rarely used, it is more natural to treat "data" as a singular form. Information Information is stimuli that have meaning in some context for its receiver. When information is entered into and stored in a computer, it is generally referred to as data. After processing (such as formatting and printing), output data can again be perceived as information. Data will be converted in to Information after processing. When information is packaged or used for understanding or doing something, it is known as knowledge. FATHER FATHER OF COMPUTER Charles Babbage was intrigued by the problem of errors in the hand calculation of complex mathematical tables. He was inspired by Charles Mohan’s logic machine which he used as a starting point engine was completed in1822 simple tables in 1833 and a working difference and was used to calculate Babbage abandoned the project and began dream, the “Analytical purpose machine that performing any type of Although his analytical Babbage did succeed in and procedures from which all work on his real Engine”, a general would be capable of digital calculation. engine was never built mapping out all the principles modern digital computers have followed. As a result he is considered to be the source of the automatic computer. COMPUTER OR A PC For layman, a PC or a Computer is like a super calculator with a really big display computer is perhaps the most useful tool ever invented. In technical terms, computer can be defined as an electronic device that accepts data, processes information in a pre – defined Fashion, according to the set of instructions provided to it and produces the desired output. The term PC, it is self explanatory. PC stands for Personal Computer as it is your own computer you are working upon. This term was adopted by IBM, the largest manufacturer of computer, to describe its first desk sized computers. Computers differ in variety and size – from a simple playing computer like spectrum to large mainframe or super computer like India’s own super computer frame. You might be wondering if a computer can store a large amount of data, then it must have a huge amount of intelligence too. Ironically, the computer’s intelligence level does not equal to that of a cockroach even. Through, research is on to impart some intelligence to if of its own. The computer only follows the instructions given to it by the user. If follows the concept of what you give is what you get, which means that whatever instructions you give, accordingly would be the result. A computer Fed with wrong instructions would give you wrong results. Super Computer COMPUTERS IN HUMAN LIVES The number of ways that computers affect human lives is uncountable. Computers can perform all those functions that a human being can do to a certain extent, but at a much faster speed and with greater accuracy. Computers are used in banks to take care of the accounting system and keep track of the enormous amount of money. Although all these tasks are done manually also, but it takes as great deal of time. If it takes about a month to make the balance sheet, a computer can make it in a few hours. Computers help you perform tasks like account handling; taking out complex reports, balance sheets, etc in a much shorten span and the results would also be very accurate. Let us take an example that you have an account in a bank which is fully computerized throughout the country. You leave an account in one of its branch in Colombo but at present you are in Vavuniya and you wish to encase a cheque. You need not call up Colombo branch, and confirm your account and perform other formalities. The cashier at Vavuniya branch of the bank would check up your bank account number of Colombo on computer and if it is there and you have the essential amount of money in your account, your cheque will immediately get encased see how simple it is with a computerized system! Now let us take up an example of an architect who designs your houses and buildings. Suppose he has been asked to design a housing complex with each lat of about 2000 sq.ft. According to the dimensions of the area and the number of houses required, he would draw the design or layout of that complex, which could take about a month or so. Let us suppose, he completes the project and is given another assignment for another housing complex, but with a greater area of say 2500 sq.ft. Now if the architect starts off with the drawing it right. From the beginning it would take another month or so. Don’t you think it consumes too much time? There is a possibility that he could commit some mistakes which will head to redoing of the same job. A computer can provide a great deal of help in this context also If you have a certain program in your computer that could help you draw the layout according to the dimensions and many other things you specify the time of drawing could be reduced to a few hours or even less. More over, if you get a new assignment to draw the same design with a greater area, you would be able to finish it in relatively no time, if you have saved the previous assignment, in the computer. So a computer makes the job much simpler and easier and most of all, the least time consuming. These examples are just a fraction of the world-wide trend about the various jobs that a computer can perform computers are used broadly even in educational institutions, by doctors, in business for guiding astronauts through space and much more. We have developed a society that is almost dependent on computerized system of functioning. So it becomes very essential to have the basic knowledge of the computer system. A COMPLETE COMPUTER SYSTEM The computer system comprises of Hard Ware, Soft Ware, Live Ware and Firm Ware. Total computer systems. Hard Ware Soft Ware Live Ware Firm Ware Hard Ware All the tangible devices which are uses in computerize systems. Soft Ware These are the program devices the hard ware and perform different task. These including operating system like DOS, Productively soft ware like spooling. Live Ware The human involvement for the computer systems. A computer system like information systems managers, system analysts, programmers etc. Firm Ware Firmware is a big program E.g.:- Boot Strap Program AGE OF COMPUTERS 1946 J.Presper Eckert, John Manchely and a team of so complete the electronic numerical intergrator and computer (ENIAC). The first large – scale electronic digital computer weights 50 tons, stands two stories, and covers 15000 square feet. 1947 Grace Hopper documents the first computer bug, a tread moth in a cabinet of the Mark II. 1949 Mource Wilkes of England’s Cambridge University builds the first stored – program Computer. 1950 1951 The first computer of use binary or digital mathematics. [EDVAC] The University Automatic computer. The first American commercially Produced this computer. 1953 1956 1959 1960 IBM introduces the first magnetic tape device. The model 726. The term “Artificial Intelligence” is corned by MC curtly. Commercial and Business oriented language (COBOL) is created. The first modern computer generation ends as vacuum tubes punched cards and machine code give way to 2nd generation transistors magnetic tape and languages in computer design and operation. 1965 The 3rd generation is developing by tom Kurtz and John Kemeny of Dortmaith Collage. 1967 1969 The 3rd generation is under way with IC. The Intel 4004 becomes the first micro processor and paves the way for the micro computer. 1975 The Cray 1 super computer is introduced as the fastest computer on earth. 1977 1978 Introduces the Apple II Personal Computer. VisiCalc, Electronic spread sheet software is created by Don Brick in. 1979 1981 Micro International releases word start a word processing program. The IBM PC debuts Microsoft’s MS – DOS becomes its standard operating software. 1983 Lotus 123 takes VisiCalc’s place as the leading spread sheet program marketed by company founder, Mitch Kaptur windows is presented by Microsoft. 1985 1990 The C++ programming language is developed. The advent of parallel processing and greatly increased processing power make this the year of Artificial Intelligence. 1992 1993 2000 Apples announce “Personal Digital Assistant”. Intel PC chips; Pentium developed. Experts predict that computers containing a billion processors will be technology feasible exceeding the power of the human brain. CLASSIFICATION OF COMPUTERS Classification of Computers we can basically divide in to 3 sections. Based on generation, size and data representation. Generations: 1 to 5 Generation & Time Period First Generation 1946 — 1956 Use of vacuum tubes, large, limited memory, jobs execution coordinated manually, and speed up to 10,000 ips. Second Generation 1957— 1963 Use of transistors, more reliable, less heat generation, less power requirement, speed 200,000 - 300,000 ips. Third Generation 1964 — 1979 • Use of Integrated Circuits (ICS) by printing hundreds and thousands of tiny transistors on to small silicon chips • Speed up to 5 Million Instructions Per Second (MIPS) • Use of operating systems that automated the running of programs & communications between CPU & peripheral devices. • Availability of hardware independent programming. Fourth Generation 1980s Use of LS1 & VLSI circuits, costs fallen to a very low level, large memory & storage, speed up to 200 MIPS Fifth Generation 5 generation computers will be Artificial Intelligence Systems called Al computers, which simulate the human brain. Expert systems also fall into this category. Size: Micro, Mini, Mainframe, Super Micro Computers A microcomputer is a complete computer on a smaller scale and is generally a synonym for the more common term, personal computer or PC, a computer designed for an individual. A microcomputer contains a microprocessor (a central processing unit on a microchip), memory in the form of read-only memory and random access memory, I/O ports and a bus or system of interconnecting wires, housed in a unit that is usually called a motherboard. In an ascending hierarchy of general computer sizes, we find: • An embedded systems programming computer, which is embedded in something and doesn't support direct human interaction but nevertheless meets all the other criteria of a microcomputer • Microcomputer • Workstation, as used to mean a more powerful personal computer for special applications • Minicomputer, now restyled a "mid-range server" • Mainframe or mainframe computer, which is now usually referred to by its manufacturers as a "large server" • Supercomputer, formerly almost a synonym for "Cray supercomputer" but now meaning a very large server and sometimes including a system of computers using parallel processing • A parallel processing system is a system of interconnected computers that work on the same application together, sharing tasks that can be performed concurrently Mini Computers A minicomputer, a term no longer much used, is a computer of a size intermediate between a microcomputer and a mainframe. Typically, minicomputers have been stand-alone computers (computer systems with attached terminals and other devices) sold to small and mid-size businesses for general business applications and to large enterprises for department-level operations. In recent years, the minicomputer has evolved into the "mid-range server" and is part of a network. IBM's AS/400e is a good example. Mainframes Mainframe is an industry term for a large computer, typically manufactured by a large company such as IBM for the commercial applications of Fortune 1000 businesses and other large-scale computing purposes. Historically, a mainframe is associated with centralized rather than distributed computing. Today, IBM refers to its larger processors as large servers and emphasizes that they can be used to serve distributed users and smaller servers in a computing network. Super Computers A supercomputer is a computer that performs at or near the currently highest operational rate for computers. A supercomputer is typically used for scientific and engineering applications that must handle very large databases or do a great amount of computation (or both). At any given time, there are usually a few well-publicized supercomputers that operate at the very latest and always incredible speeds. The term is also sometimes applied to far slower (but still impressively fast) computers. Most supercomputers are really multiple computers that perform parallel processing. In general, there are two parallel processing approaches: symmetric multiprocessing (SMP) and massively parallel processing (MPP). Perhaps the best-known builder of supercomputers has been Cray Research, now a part of Silicon Graphics. Some supercomputers are at "supercomputer center," usually university research centers, some of which, in the United States, are interconnected on an Internet backbone known as vBNS or NSFNet. This network is the foundation for an evolving network infrastructure known as the National Technology Grid. Internet2 is a university-led project that is part of this initiative. At the high end of supercomputing are computers like IBM's "Blue Pacific," announced on October 29, 1998. Built in partnership with Lawrence Livermore National Laboratory in California. Blue Pacific is reported to operated at 3.9 teraflop (trillion operations per second), 15,000 times faster than the average personal computer. It consists of 5,800 processors containing a total of 2.6 trillion bytes of memory and interconnected with five miles of cable. It was built to simulate the physics of a nuclear explosion. IBM is also building an academic supercomputer for the San Diego Supercomputer Center that will operate at 1 teraflop. It's based on IBM's RISC System/6000 and the AIX operating system and will have 1,000 microprocessors with IBM's own POWER3 chip. At the lower end of supercomputing, a new trend, called clustering, suggests more of a build-it-yourself approach to supercomputing. The Beowulf Project offers guidance on how to "strap together" a number of off-the-shelf personal computer processors, using Linux operating systems, and interconnecting the processors with Fast Ethernet. Applications must be written to manage the parallel processing. Data Representation: Analog, Digital, Hybrid. Analog Computer An analog computer operates in a completely opposite way to the digital computer. For a start, all operations in an analog computer are performed in parallel. Secondly, data are represented in an analog computer as voltages, a very compact but not necessarily robust form of storage (prone to noise corruption). A single capacitor (equivalent to the Digital’s computer use of a transistor) in an analog computer can represent one continuous variable. The Heath kit Educational Analog Computer is completely self-contained and contains nine DC operational amplifiers with provision for balancing without removing problem setup. It also features three initial condition power supplies, five coefficient potentiometers, four sets of relay contacts, an electronically regulated power supply and a built-in repetitive oscillator for automatic operation. The complete EC-1 kit also contains an assortment of precision resistors, capacitors, special silicon diodes and patch cords for setting up scores of complex computer problems easily and accurately. Digital Computer The digital computer is a sequential device, in general, operating on data one step at a time; in addition the digital computer represents data internally using a quite verbose but very robust form of representation called binary. Thus a single transistor in a digital computer can only store two states, on and off. Obviously to store a number to any sensible degree of precision, many transistors are required. Hybrid Computer A computer that processes both analog and digital data. A Hybrid Computer is a combination of computers that are capable of inputting and outputting in both digital and analog signals. A hybrid computer system setup offers a cost effective method of performing complex simulations. Purpose: Special, General Depending on the purpose we can categorize the computers mainly on to two. Special Purpose Computers Special Purpose Computers are used for special purposes like scientific researches, atomic weapon researches, designing sophisticated vehicles, weather forecasting etc. Normally super computers come under special purpose computers as we discussed earlier. General Purpose Computers General Purpose Computers are the normal computers we are using. THE FIVE GENERATIONS OF COMPUTERS The history of computer development is often referred to in reference to the different generations of computing devices. Each generation of computer is characterized by a major technological development that fundamentally changed the way computers operate, resulting in increasingly smaller, cheaper, and more powerful and more efficient and reliable devices. Read about each generation and the developments that led to the current devices that we use today. First Generation - 1940-1956: Vacuum Tubes The first computers used vacuum tubes for circuitry and magnetic drums for memory, and were often enormous, taking up entire rooms. They were very expensive to operate and in addition to using a great deal of electricity, generated a lot of heat, which was often the cause of malfunctions. First generation computers relied on machine language to perform operations, and they could only solve one problem at a time. Input was based on punched cards and paper tape, and output was displayed on printouts. The UNIVAC and ENIAC computers are examples of first-generation computing devices. The UNIVAC was the first commercial computer delivered to a business client, the U.S. Census Bureau in 1951. Second Generation - 1956-1963: Transistors Transistors replaced vacuum tubes and ushered in the second generation of computers. The transistor was invented in 1947 but did not see widespread use in computers until the late 50s. The transistor was far superior to the vacuum tube, allowing computers to become smaller, faster, cheaper, more energy-efficient and more reliable than their first-generation predecessors. Though the transistor still generated a great deal of heat that subjected the computer to damage, it was a vast improvement over the vacuum tube. Secondgeneration computers still relied on punched cards for input and printouts for output. Second-generation computers moved from cryptic binary machine language to symbolic, or assembly, languages, which allowed programmers to specify instructions in words. High-level programming languages were also being developed at this time, such as early versions of COBOL and FORTRAN. These were also the first computers that stored their instructions in their memory, which moved from a magnetic drum to magnetic core technology. The first computers of this generation were developed for the atomic energy industry. Third Generation - 1964-1971: Integrated Circuits The development of the integrated circuit was the hallmark of the third generation of computers. Transistors were miniaturized and placed on silicon chips, called semiconductors, which drastically increased the speed and efficiency of computers. Instead of punched cards and printouts, users interacted with third generation computers through keyboards and monitors and interfaced with an operating system, which allowed the device to run many different applications at one time with a central program that monitored the memory. Computers for the first time became accessible to a mass audience because they were smaller and cheaper than their predecessors. Fourth Generation - 1971-Present: Microprocessors The microprocessor brought the fourth generation of computers, as thousands of integrated circuits were built onto a single silicon chip. What in the first generation filled an entire room could now fit in the palm of the hand. The Intel 4004 chip, developed in 1971, located all the components of the computer - from the central processing unit and memory to input/output controls - on a single chip. In 1981 IBM introduced its first computer for the home user, and in 1984 Apple introduced the Macintosh. Microprocessors also moved out of the realm of desktop computers and into many areas of life as more and more everyday products began to use microprocessors. As these small computers became more powerful, they could be linked together to form networks, which eventually led to the development of the Internet. Fourth generation computers also saw the development of GUIs, the mouse and handheld devices. Fifth Generation - Present and Beyond: Artificial Intelligence Fifth generation computing devices, based on artificial intelligence, are still in development, though there are some applications, such as voice recognition, that are being used today. The use of parallel processing and superconductors is helping to make artificial intelligence a reality. Quantum computation and molecular and nanotechnology will radically change the face of computers in years to come. The goal of fifth-generation computing is to develop devices that respond to natural language input and are capable of learning and self-organization. COMPUTER GENERATIONS BRIEFLY EXPLANATION First Generation [1946 – 1955] We have just read about the first generation of computer. These computers used value (vacuum tube) technology and had the main limitations of very large electric power consumption and very little reliability. In 1946, Eckert and Mouchley formed their company the UNIVAC divitision of Remington Rand, Inc. This company made the first commercial computer UNIVAC division in 1951. The UNIVAC had a memory capacity of 1000 words. It used magnetic tapes as input or output devices. It has used to predict the election of Dwlight D.Eisen howen (one of the president of USA) in 1952. A similar computer whirlwind one was built in 1951 by the Massachusetts Institute of Technology, USA. It had a memory capacity of 2048 word. In 1953 IBM installed its first computer the IBM 701 late in 1954 the IBM developed a general purpose computer. IBM 650 computer was the most popular one during that time. To over come the small storage capacity of IBM 650 and to produce a more efficient system the IBM developed IBM – 1401 add RAMAC 350. The first generation computers were characterized by electronic tube circuitry. Hence they were very large air – conditioned room. They had small internal storage and were relatively showed. The First generation machines used punched paper tape, punched card, magnetic wire, magnetic tape and printers as input or output devices. Second Generation [1957 – 1963] With the advent of transition technology, a second generation of computer comes into existence. These computers were smaller in size, more reliable and highly efficient. These machines used English like language know as High Level Language (HLL) for ease of operation and application in business and scientific analysis many American and European companies manufactured these machines. One of them the IBM – 1401 was the most popular and some of the IBM – Organization use this model even today. These computers were called the generations of computer. They have faster access and were more reliable than the first generation of computer. They were characterized by both vacuum tube (value) and discrete transistor logic. By this time a wider range of input or output devices such as higher performance magnetic tapes, magnetic drums and early during the second generation magnetic disks were available computer language such as introduced. The picture computer IBM – 7070 is FORTRAN and ALGOL were of a second generation shown below. The second generation of computers started with the introduction of transistorized computer. The first of these, the IBM 7090 was delivered in 11959 which were followed by the CDC 1604, The Phil co 2000 and Remington rondo’s UNIVAC, LARC. Other widely used second generations of computer were • IBM 1620 • IBM 1401 • IBM 7094 Third Generation [1964 – 1979] In the sixtieth Integrated Circuits (IC) popularly know as ICs came in the field of micro – electronics computers, that use a large junk of electronic components were substantially of price reduction as well machines consumed were highly reliable. These machines programs like real time multiprogramming, techniques used operation more versa tike benefited both from the point as size reduction these very little power and system, and data base management, IBM – 370, some of the most popular machine of this generation. Many others models are given in table. Manufacturer Moore school of Model Electrical ENIVAC, EDVAC Engineering Cambridge University Univas Burroughs Honey Well IBM EDSAC Univac I, Univac II E101, Burroughs 2022 Data matic 1000 Mark II, Mark III, 604 electronic punch, calculating IBM 650 IBM 702 IBM 704 IBM 705 IBM 709 National cash Register RC4 CRC, 1024, 102D BIZMAC I, BIZMAC II In the third generation computers more than were user could work with the computer at the same time, where as first and second generation of computers worked on a one – to – one basis. Almost all computers introduced after 1966 were said to be third generation computer. Most of the main frame computers use till the early 1980’s were third generation computers only a good. Fourth Generation [1980 – Present] Forth generation of computers were produced after 1980 the fourth generation computer is used to designate micro computers which use large scale integrated circuits (LSI) and very large scale integrated circuits (VLSI) in the memory unit. The invention of micro process or chip has created a revolution in the reduction of price and size of this generation machines. These machines have followed advantages over other generation. 1. These computers use advanced techniques to feed. 2. Data into them and to bring out processed data for use of the outside world. Then can even be connected with the satellite communication links to trans form information from one hart of the world at very high speed. These Machines use advance application. 3. These machines use advance software such as process controverts, computer aided design (CAD), electronic spread sheet (Lotus 123) and data base management. Because of this these machines of table size type writer have the same power which was available in very large computers of the third generation. Fifth Generation [Future] We are presently straddling for the line between fourth and fifth generation computers. In 1981 a group of Japanese design and build the fifth generation machines this consortium believed generation machines. This consortium believed it was possible for such a machine to per for the following. Accept Spoken instructions and such graphic images as photographs as data input. Collect select and store useful data form newspapers, books tape recorded speeches and other common sources. Translate foreign languages research and provide answers to questions by using all available data. Learn from its own experiences program itself. The US computer industry was at a dosed vantage in early phases of the fifth generation race because antitrust laws restricted. The ability of companies to co-operate by comparison the Japanese government brought together all of its resources and all companies with in its electro nice industry for a coopered fives concerted effort since these early days the government in the United States has sanctioned special research and development cooperatives formed by a number of computer companies induction some of the largest companies part equally IBM hare established special developmental efforts budgets for advanced computing capabilities. The fifth generation of computers is seen as having increased processing capabilities, data handling and storage facilities software will respond to the natural language of people. The new technologies discussed below are seen as heys to implementing fifth generation systems. Optics and super conductive materials Parallel Processing Artificial Intelligence (AI) Language translation and non traditional input Special purpose machines ARTIFICIAL INTELLIGENCE Computers are starting to simulate human thought and argument one type of software application is known as Artificial Intelligence (AI). This growing one of development scythe sizes computer science psychology linguistics and other specialized fields to perform tasks with human live logic. Among 5th AI developments expected in fifth generation computers are heuristic problem solving techniques. The term heuristic describes are solved through application of general rules and information based on experience. Instead of following precise sequence of instructions to devices solutions heuristic software applies rules proven to be effective in the past as example heuristic techniques are used to develop programs that play chess vast human of moves are possible in a same of chess with heuristic capabilities the computer as able to evaluate different moves to bulls a games strategy thus. The chess playing computer able to respond to variable situation is several different ways computers scientists around the world are building system that can learn form experience and are able to apply this in for motion to new situations. MAIN CIRCUIT BOARD OF A PC A motherboard is the physical arrangement in a computer that contains the computer's basic circuitry and components. On the typical motherboard, the circuitry is imprinted or affixed to the surface of a firm planar surface and usually manufactured in a single step. The most common motherboard design in desktop computers today is the AT, based on the IBM AT motherboard. A more recent motherboard specification, ATX, improves on the AT design. In both the AT and ATX designs, the computer components included in the motherboard are: • The microprocessor • (Optionally) coprocessors • Memory • Basic input/output system (BIOS) • Expansion slot • Interconnecting circuitry Additional components can be added to a motherboard through its expansion slot. The electronic interface between the motherboard and the smaller boards or cards in the expansion slots is called the bus. Bus In a computer or on a network, a bus is a transmission path on which signals are dropped off or picked up at every device attached to the line. Only devices addressed by the signals pay attention to them; the others discard the signals. According to Winn L. Rosch, the term derives from its similarity to autobuses that stop at every town or block to drop off or take on riders In general, the term is used in two somewhat different contexts: (1) A bus is a network topology or circuit arrangement in which all devices are attached to a line directly and all signals pass through each of the devices. Each device has a unique identity and can recognize those signals intended for it. (2) In a computer, a bus is the data path on the computer's motherboard that interconnects the microprocessor with attachments to the motherboard in expansion slots (such as hard disk drives, CD-ROM drives, and graphics adapters). Chips Chip" is short for microchip, the incredibly complex yet tiny modules that store computer memory or provide logic circuitry for microprocessors. Perhaps the best known chips are the Pentium microprocessors from Intel. The PowerPC microprocessor, developed by Apple, Motorola, and IBM, is used in Macintosh personal computers and some workstations. AMD and Cyrix also make popular microprocessor chips. There are quite a few manufacturers of memory chips. Many specialpurpose chips, known as application-specific integrated circuits, are being made today for automobiles, home appliances, telephones, and other devices. A chip is manufactured from a silicon (or, in some special cases, a sapphire) wafer, which is first cut to size and then etched with circuits and electronic devices. The electronic devices use complementary metal-oxide semiconductor technology. The current stage of micro-integration is known as Very Large-Scale Integration (VLSI). A chip is also sometimes called an IC or integrated circuit. Ports On computer and telecommunication devices, a port (noun) is generally a specific place for being physically connected to some other device, usually with a socket and plug of some kind. Typically, a personal computer is provided with one or more serial ports and usually one parallel port. The serial port supports sequential, one bit-at a-time transmission to peripheral devices such as scanners and the parallel port supports multiple-bit-at-a-time transmission to devices such as printers. Expansion Slots In computers, a slot, or expansion slot, is an engineered technique for adding capability to a computer in the form of connection pinholes (typically, in the range of 16 to 64 closely-spaced holes) and a place to fit an expansion card containing the circuitry that provides some specialized capability, such as video acceleration, sound, or disk drive control. Almost all desktop computers come with a set of expansion slots. These help ensure that you'll be able to add new hardware capabilities in the future. SIMM A SIMM (single in-line memory module) is a module containing one or several random access memory (RAM) chips on a small circuit board with Pins that connect to the computer motherboard. Since the more RAM your computer has, the less frequently it will need to access your secondary storage (for example, hard disk or CD-ROM); PC owners sometimes expand RAM by installing additional SIMMs. SIMMs typically come with a 32 data bit (36 bits counting parity bits) path to the computer that requires a 72-pin connector. SIMMs usually come in memory chip multiples of four megabytes. The memory chips on a SIMM are typically dynamic RAM (DRAM) chips. An improved form of RAM called Synchronous DRAM (SDRAM) can also be used. Since SDRAM provides a 64 data bit path, it requires at least two SIMMs or a dual in-line memory module (DIMM). RIMM In a computer, a RIMM is a memory module developed by Kingston Technology Corp. that takes up less space inside the computer than the older DIMM module and has different PIN characteristics. A RIMM has a 184-pin connector and an SO-RIMM module has a 160-pin connector. An SO-RIMM is smaller and is used in systems that require smaller form factors. While RIMM is commonly believed to stand for "Rambus inline memory module," Kingston Technology has trademarked "RIMM" and uses only that term. A RIMM module consists of RDRAM chips that are attached using a thin layer of solder, a metal alloy that, when melted, fuses metals to each other. Solder balls on each chip create a metal pathway used to conduct electricity. DIMM A DIMM (dual in-line memory module) is a double SIMM (single inline memory module). Like a SIMM, it's a module containing one or several random access memory (RAM) chips on a small circuit board with pins that connect it to the computer motherboard. A SIMM typically has a 32 data bit (36 bits counting parity bits) path to the computer that requires a 72-pin connector. For synchronous dynamic RAM (SDRAM) chips, which have a 64 data bit connection to the computer, SIMMs must be installed in in-line pairs (since each supports a 32 bit path). A single DIMM can be used instead. A DIMM has a 168-pin connector and supports 64-bit data transfer. It is considered likely that future computers will standardize on the DIMM. VDU Interface A device used for the real-time temporary display of computer output data. Note: Monitors usually use cathode-ray-tube or liquid-crystal technology. Synonyms video display terminal, video display unit, visual display unit. VDU, or "video terminal", "video display terminal", VDT, "display terminal") A device incorporating a cathode ray tube (CRT) display, a keyboard and a serial port. A VDU usually also includes its own display electronics which store the received data and convert it into electrical waveforms to drive the CRT. VDUs fall into two categories: dumb terminals and intelligent terminals (sometimes called "programmable terminals"). Early VDUs could only display characters in a single preset font, and these were confined to being layed out in a rectangular grid, reproducing the functionality of the paper-based teletypes they were designed to replace. Later models added graphics facilities but were still driven via serial communications, typically with several VDUs attached to a single multi-user computer. This contrasts with the much faster single bitmap displays integrated into most modern single-user personal computers and workstations. The term "Display Screen Equipment" (DSE) is used almost exclusively in connection with the health and safety issues concerning VDUs. HISTORY OF THE MOTHERBOARD Before starting to look at the motherboard inn detail it is worthwhile examining the g\history of its development over the years. Motherboards have changed radically in order to accommodate the latest developments in technology such as new CPUs, different types of memory, different expansion buses (and cards), and to some extend to meet the need for smaller system units. Looking back, the earliest computers were often produced as kits aims at hobbyist and electronic enthusiast. With these kits the electrical components were installed using a commercial board approach with the manually soldered components. The customer essentially built the computer according to a set of assembly instructions and standard components. As computer design and manufacturing technique developed, computers began to incorporate a separate simple circuit board with a logical layout for placing the electrical components. This was basically the first motherboard and led to the development of chip sockets and components pinholes wit an etched circuit. This enables a production assembly line of workers to manually insert and solder all discrete parts in place. With the development of new manufacturing techniques such as wave soldering and machines for large-scale automation of components installation quantity and production rates improved. With the rapid development of manufacturing technique to increase the no\umber of transistors per chip offered by Large Scale Integration (LSI) and then Very Large Scale Integration (VLSI), motherboard design has evolved to the point where the number of physical components required for a system has been reduced dramatically. When IBM introduced the first popular PC 5150 in 1981, the motherboard contained a large number of memory chips conventionally taking up a larger part of the motherboard surface area. Other semiconductors devices were installed in a simple row format alone with an extends system bus offering five 8 bit ISA standard expansion card slots. The physical size of this early motherboard was largely a reflection of the number of chips supported and design of bus and peripheral ports. The original motherboard used in the PC 5150 had over 100 Integrated Circuit (IC) chips and naturally the introduced of LSI and VSLI led to a reduction of the number of support chips required. This physical size and the layout of major components are termed as a board from factor and as we shall see later, are used in identifying difficulty types of motherboard. The first real standard motherboard was introduced with the IBM PC XT in 1983. The number of expansion slots was increased from five to eight, with less space allotted between the slots. This motherboard set a standard for board design and was taken up by many other PC manufactures in the transition to 16 bit processing; the form factory this board become known as the Baby-AT. In 1984, IBM brought out a new 16-bit processor PC called the IBM PC AT. This used a large physical size from factor boars then the Baby At and was called Full Size AT. This broad has eight bit slots, with six of those having a slot extension to support 16 bit PC cards. Many IBM compatible suppliers incorporating the 16 bit features of the Full Size AT board manufactured the Baby-AT board. These boards were so similar that the Baby- AT could easily replace the Full Size AT board as an upgrade. Both boards initially had a single 5 pin DIN keyboard connectors mounted on the motherboard with a hole in the computer chassis rear panel to provide access. The 5-pin DIN keyboard socket on this motherboard was eventually replaced with a mini-DIN 6-pin PS/2 type keyboard socket before this motherboard design was eventually superseded. During 1987 Western Digital created new motherboard from faction called the LPX and mini-LPX. These boards were fro incorporation slim-line or low profile computers. A major difference with this motherboard is that PC expansion cards cannot be installed vertically because of the limited computer casing height. Instead these boards have a single system bus slot on the motherboard from which a special extender card or riser card is mounted at right angles. The riser card has built-in expansion slot and supports PC expression card mounted horizontally. LPX or Mini-LPX from factor motherboards can easily be recognized, external to a computer by the use of horizontal chassis opening for expanses slots on desktop or vertical slots when the motherboard is mounted in a tower computer case. An LPX board has two PS/2 type connectors (one fro the keyboard and one for a mouse) mounted on the motherboard with two 9 pin serial sockets and single parallel sockets. Another from factor motherboard, called the NLX is very similar to the board to be used in PCs until the mid to late 1990s. By then a new motherboard from factor called ATX began to replace the Baby-AT. In 1997 Intel introduced a new motherboard from factor called ATX. Combining build and components qualities from both the Baby-AT and LPX boards with new boards design features; this motherboard is the basis for the current most popular standard. It is also has the new 20 pin power supply connectors with supplied +3.3.V for processor supply. Because of the advances in VLSI motherboard manufactures have been able to save a considerable amount of space in their designs. This extra many of the functions, such as video audio and new networking that previously required additional expansion card. Just as with the original AT deign many manufacturers have introduced a compact version of the ATX format motherboard called the Mini ATX. With the integration of more and more functions onto the motherboard the need for expansion slots has deceased. Therefore instead of providing seven expansion slot as with the ATX from factor the Mini ATX motherboard typically has just three or four factories the Mini means that the Mini ATX motherboard can be filtered in to cheaper more compact system unit cases. The major drawback of the Mini ATX from memory slot and only allow one or two Dual In-Line Memory Modules (DIMMs) to be installed. Identifying the from factors of a motherboard can be quite difficult, although most manufactures will label product to aid identification. Naturally any motherboard document should clearly state the from factor. PROGRAMMING LANGUAGES Hundreds of programming languages exist. Only a few, however, are used widely enough today for the industry to recognize them as standards. Most of these are high-level languages that work on a variety of computers. This section discusses these programming languages, their origins, and their primary purpose. Although the Java programming language is used in many business applications today; it originally was used primarily for Web development. Thus, Java is discussed in the Web page development section of this chapter. To illustrate the similarities and differences among programming languages, figures on the following pages show program code in several programming languages. The code solves a simple payroll problem — computing the gross pay for an employee. The steps to compute gross pay can vary from one system to another. The examples on the following pages use a simple algorithm to help you easily compare one programming language with another. To compute the gross pay, first multiply the regular time hours worked by the hourly rate of pay to obtain the regular time pay. If the employee has overtime hours, the employee’s overtime pay is 1.5 times the hourly rate of pay multiplied by overtime hours. Then, add the regular time pay and overtime pay together. BASIC John Kemeny and Thomas Kurtz developed a programming language called Beginner’s All-purpose Symbolic Instruction Code, or BASIC, in the mid-1960s at Dartmouth College. Kemeny and Kurtz designed BASIC for use as a simple, interactive problem-solving language. BASIC originally was intended as the language used in a student’s first programming course because it is so easy to learn and use. Today, BASIC is used on both personal computers and mid-range servers to develop some business applications. Many versions of BASIC exist, including QBasic, QuickBasic, and MS-BASIC. Visual Basic Developed by Microsoft Corporation in the early 1990s, Visual Basic is a Windows based Application that assists programmers in developing other event-driven Windows-based applications. The first step in building a Visual Basic application is to design the graphical user interface using Visual Basic objects. Visual Basic objects, or controls, include items such as command buttons, text boxes, and labels. Next, you write any code needed to define program events. An event in Visual Basic might be the result of an action initiated by a user. When a user clicks an object in a Visual Basic application, the application executes the Click event. You define Visual Basic events using code statements written in Visual Basic’s built-in programming language. COBOL COBOL (Common Business-Oriented Language) developed out of a joint effort between the United States government, businesses, and major universities in the early 1960s. Naval officer Grace Hopper, a pioneer in computer programming, was a prime developer of the COBOL language. COBOL is a procedural programming language designed for business applications. Although COBOL pro grams often are lengthy, their English- like statements make the code easy to read, write, and maintain (Figure 15-26). COBOL is especially useful for processing transactions on main frames. COBOL programs also run on other types of computers. The most popular personal computer COBOL program is Micro Focus Net Express®, which allows you to create procedural and object oriented COBOL programs and migrate them to the Web. C The C programming language, developed in the early 1970s by Dennis Ritchie at Bell Laboratories, originally was designed for writing system software. Today, a variety of software programs are written in C. This includes operating systems and application software such as word processing and spreadsheet programs. C is a powerful language that requires professional programming skills. Many programmers use C for business and scientific problems. C runs on almost any type of computer with any operating system, but it most often is used with the UNIX operating system. In fact, most of the UNIX operating system is written in C. C++ Developed in the 1980s by Bjame Sroustrup at Bell Laboratories, C++ (pronounced SEE-plus-plus) is an object-oriented programming language. C++ is an extension of the C programming language. It includes all the elements of the C language plus has additional features for working with objects, classes, events, and other object oriented concepts. Programmers commonly use C++ to develop application software, such as word processing and spreadsheet programs, as well as database and Web applications. Although C++ is an outgrowth of the C programming language, you do not need C programming experience to be a successful C++ programmer. Some programmers use a newer programming language called C# (pronounced SEE-sharp). C# com bines features of C and C++ and is best suited for development of Web applications. JAVA Developed by Sun Microsystems, Java is a compiled object-oriented programming language used to write stand-alone applications, as well as applets and servlets. Java applet examples might include input forms, rotating images, fireworks, interactive animations, or a game. Figure 15-37 shows a sample Java program and its resulting screen. The Java language is very similar to C++. One difference is that Java source code is compiled into byte code, instead of object code. The operating system cannot execute byte code. A Java interpreter executes the byte code. Java-enabled Web browsers contain Java byte code interpreters. Code segments used to create a Java application are called JavaBeans, or Beans. A JavaBeans is platform independent. This enables the code to run on any computer or operating system. Many programmers believe that Java will be the programming language of the future because of its simplicity, robustness, and portability. INTEL PROCESSORS: NOW AND THEN There might come a time when you upgrade a processor in below are details and the most popular chips manufacturers. will have to replace or order to fix a problem. Listed characteristics of some of from Intel and other 8088 This is the chip found in most of the IBM XT-class machines. The 8088 came in a 40- pin DIP package. Translated, this means the 8088 is a small, rectangular chip with two rows of 20 pins each. The original speed of this chip was 5MHz. Later versions reached a top speed of about 8MHz. 80286 Introduced in 1981 by Intel, this chip became the mainstay of the ATclass computers. The chip itself was packaged in a square called a Pin Grid Array (PGA) instead of a rectangle. The chip contained about 130,000 transistors -- about 100,000 more than the 8088. 80386 The 80386 was introduced to the market in 1985 and came in two different types: DX and SX. This chip was also packaged in the PGA configuration. The 80386 contained 250,000 transistors and also provided features like multitasking of DOS programs and a 32-bit data path. The 32-bit data path was available only in the DX version, while the SX version had a 16-bit data path. This made the SX more compatible with the 80286 computers and hardware. 80486 The 80486 chip was actually a “beefed-up” version of the 80386. The 486 processor was a composite of three other chips. The 80486 consisted of a 386 chip, a 385 cache controller and a 387 math co-processor. The 486 contained about 1.25 million transistors and 8k of internal cache memory. It provided a 32- bit data path and a built-in math co-processor. Like the 80386, the 80486 came in two types: the DX and SX. The 80486 SX had all the features of the DX version minus the math co processor. Actually, the math coprocessor was still on-board but disabled in the SX version. 80486DX2 To understand the 80486DX2, it is important to understand another Intel creation designed to increase system speed: the “Overdrive” chip. The Overdrive chip could run at two clock speeds simultaneously. If the chip was placed on a 486SX1 25MHz system board, it was placed in the socket for the co processor chip and took over for the 486SX chip. When data was passed through the Bus or memory, it was done at the speed of the processor; in this case 25MHz. This is referred to as the external clock speed. All the internal calculations were done at twice the 25MHz speed, at 50MHz. The 80486DX2 is very similar to the Overdrive chip in that it runs at a certain external speed “X MHz” but performs all internal calculations at “two times X.” 80486DX4 The plot thickens. DX4 chips used a technology developed by IBM called Clock Tripler (nicknamed “Blue Lightning”). Under an agreement with Intel, IBM manufactured 486 chips using the Intel mask. Using their own Clock Tripler technology, IBM took an Intel 486DX 25MHz chip and increased its speed to approximately 75MHz. Intel followed suit and announced the 80486DX/99MHz chip. This chip would run external speeds of 331VIHz and perform internal calculations at 99MHz. Pentium In 1993 Intel introduced the Pentium processor. The initial market response was not overwhelming, but the Pentium has now become the standard for personal computers sold today. The Pentium processor contains over 3 million transistors and provides a 64- bit data path. The first generation of Pentium chips was subject to heat problems. Computers not designed to deal with high temperatures tended to experience high failure rates. Newer versions of the Pentium chip were designed to run cooler. System boards and internal components were also designed to cope with the higher temperatures. The Pentium chips will run both internal calculations and external processing at the same speed. Another unique feature of the Pentium chip is the cache. The Pentium has two 8KB caches: one that is used for program code and another used for data cache. The Pentium chip was also designed to be fault tolerant, something Intel refers to as “superscalar.” This feature is only functional when the Pentium chip is installed on a system board that will support multiple processors. Fault tolerance simply means that when two processors are present on the system board, the second chip takes over if the first chip fails. Pentium Pro The Pentium Pro processor has a different look and design than the other chips. It is the first Intel processor to combine Level1 (L1) and Level 2 (L2) cache in the same package as the CPU. The Pentium Pro processor is a dualchip configuration that houses the Pentium Pro CPU on one side of the dualcavity package and the L2 cache memory on the other. According to Intel, this simplifies system design and saves space. The Pentium Pro processor has about 21 million transistors in total. The CPU core has 5.5 million transistors and the L2 cache has 15.5 million. The Pentium Pro was designed to support multiple Pentium Pro processors connected in parallel. The Pentium Pro is a true 32-bit processor. It operates at speeds of 200MHz. MMX Technology The MMX technology is based on a new set of instructions that are built into Intel’s Pentium microprocessors. This new instruction set enables the chip to efficiently process video and audio data. Prior to the MMX technology, multimedia operations, in video and sound, had to be handled by separate components like sound cards and enhanced video boards. These same functions can now be managed by the processor. MMX chips’ internal memory (cache memory) has doubled in size (32KB). This is the area in memory that holds recently accessed data. It is designed to speed up subsequent requests to this data. This means that more instructions and data can be stored internally in the chip, reducing the number of times the processor has to access slower external memory. Most multimedia applications run dramatically faster and smoother. To really get the most out of the new MMX chip, you must run the enhanced MMX applications that have been written to exploit the true power of the technology. Pentium II The Pentium II processor is available in speeds from 233MHz to 450MHz. It utilizes the innovative 0.25 micron manufacturing process that enables these CPUs to include over 7.5 million transistors. This results in more power in less space. The processor core is packaged in the Single Edge Contact (SEC) cartridge enabling ease of design and flexible motherboard architecture. The processor also includes MMX technology. The Dual Independent Bus (DIB) architecture increases bandwidth and performance over single-bus processors. Pentium III The new Intel Pentium III processor is groundbreaking in terms of graphics capabilities. The chip has been built to exploit many of the new and expanding 3-D graphic images and their manipulation. The following are some of the highlights of the Pentium III. Added 70 new instruction sets for enhanced graphics, video and sound. The Pentium III processor introduced a new processor instruction set called Streaming SIMD Extensions (SSE). Single-instruction, Multiple Data (SIMD) was the instruction set used by the MMX processor to improve multimedia performance. The Pentium III SSE instruction set was designed to further enhance multimedia performance. An embedded serial number to help companies with an inventory of computers. This feature will also enhance on line security transactions. Although it also raises some very serious privacy concerns. Clock speeds in excess of 800 MHz. Pentium IV Pentium 4 (P4) is the Intel processor (codenamed Willamette) that was released in November 2000. The P4 processor has a viable clock speed that now exceeds 2 Gigahertz (GHz) - as compared to the 1 GHz of the Pentium 3. P4 had the first totally new chip architecture since the 1995 Pentium Pro. The major difference involved structural changes that affected the way processing takes place within the chip, something Intel calls Net Burst micro architecture. Aspects of the changes include: a 20-stage pipeline, which boosts performance by increasing processor frequency; a rapid-execution engine, which doubles the core frequency and reduces latency by enabling each instruction to be executed in a half (rather than a whole) clock cycle; a 400 MHz system bus, which enables transfer rates of 3.2 gigabytes per second (GBps); an execution trace cache, which optimizes cache memory efficiency and reduces latency by storing decoded sequences of micro operations; and improved floating point and multimedia unit and advanced dynamic execution, all of which enable faster processing for especially demanding applications, such as digital video, voice recognition, and online gaming. P4's main competition for processor market share is the AMD Athlon processor. Celeron The Celeron is Intel’s entry into the low-end microprocessor market. It is based on the same architecture as the Pentium II. However, it lacks some of the performance features of the Pentium II family. The newest of the Celeron CPUs include an L1 and L2 on-board cache. This configuration means that the cache is actually accessed at the same clock speed as the processor operates. When comparing the Celeron’s L2 cache to the Pentium II’s cache you will find it somewhat smaller (i28 KB) as compared to the Pentium II’s (512 KB) cache. However, since the Celeron’s cache is built in and the Pentium’s is not, their effective L2 speeds are roughly the same. The Celeron processor supports clock speeds up to 466 MHz and can be mounted in a Slot 1 motherboard. Intel is marketing this chip for the entry level PC, capable of providing performance solutions geared to the home and light business use. Itanium Processor The Itanium processor, formerly known as the Merced IA- 64, is unique with its Slot M configuration and L3 cache. The L3 cache is small in physical size and is not located on-board the chip itself but is bundled instead within the processor package. Currently there are two flavors: the 800 MHz and 1000MHz versions. Motorola Chip Family The Motorola chip set is not quite as well known in the PC market as Intel. For the most part, it is associated with the Apple computer line. 68000 Introduced in 1979, the 68000 chip is closely associated with the Apple computer. The 68000 chip employed a 32- bit design and used a 16-bit data Bus. The 68000 was far ahead of Intel’s efforts at the time. 68010 In 1982, Motorola introduced the 68010 chip. The major difference between the68000 and the 68010 was the addition of virtual memory support. This chip also incorporated internal cache which made the processing of subroutines much faster. This chip did not find widespread use in the computer world but was used extensively in Motorola’s component division. 68020 This chip was introduced in 1984 as the first full 32-bit chip in the Motorola line. The 68020 had the ability to access 4 GB of RAM and utilized floating point processing capabilities. It was used in the Macintosh II and found widespread use in minicomputers as well. 68030 Introduced to the market in 1987, the 68030 had all the features of the 68020 plus demand page memory management. Other enhancements to the chip also increased the speed of the chip. It was used most widely used in the Macintosh II series of computers. 68040 In 1989, Motorola’s answer to Intel’s 486 was the 68040. However, the 68040 did not gain the market share that Intel’s486 enjoyed. Power PC Apple, IBM and Motorola all joined together to develop the PowerPC family of chips. PowerPC stands for Performa2 Optimization with Enhanced RISC. Currently Apple incorporates the chip in its PowerMac series of computers. This chip can also be used in everything from laptops to computers functioning as servers. Other Chips Cyrix Cyrix (SYE-rihks) is a family of low-end, low-cost microprocessors intended for personal computers and personal information devices. Cyrix competes with Intel in the low-cost, low-end market for PC microprocessors. Typically, Cyrix has been able to under-price Intel for comparable low-end microprocessors. Cyrix began making semiconductors in 1988. Its first product was a math coprocessor. About 1992, it introduced its first microprocessors that would handle the instruction set specified by Intel’s 486 microprocessors. AMD K6 The AMD K6 is AMD’s answer to the Intel Pentium series of microprocessors. Although it is considerably less expensive than the Pentium II processors, according to many industry based benchmarks the K6 has slightly better performance. The KG has 64K of Li and L2 cache. The K6 processor can be mounted in a Socket 7 based motherboard. AMD offers multiple K6 versions which support a 66 MHz bus and operate at clock speeds starting at 166 MHz. There is also a 266 version, referred to as the K6+. The K6+ (266) operate at about 2.5 volts of power at a very low heat output making it an ideal candidate for the laptop computing market. K7 (Athlon) The K7 processor was the first AMD product to support a 200 MHz bus and to reach a 1 Gigahertz (one billion) clock speed. The K7 classification was actually the development name for the Athlon processor. Compaq and Gateway are among companies that manufacture computers that include the 1 GHz Athlon. As the successor to AMD’s K6 microprocessor the K7 compares favorably to Intel’s Pentium III. The K7 has a 128 KB Li and L2 cache that is built into the chip itself, significantly increasing performance. THE COMPONENTS OF A COMPUTER A computer consists of a variety of hardware components that work together with software to perform calculations, organize data, and communicate with other computers. These hardware components include input devices, output devices, a system unit, storage devices, and communications devices. Input Devices An input device is any hardware component that allows a user to enter data and instructions into a computer. Six commonly used input devices are the keyboard, mouse, microphone, scanner, digital camera, and PC camera. A computer keyboard contains keys that allow you to type letters of the alphabet, numbers, spaces, punctuation marks, and other symbols. A computer keyboard also contains other keys that allow you to enter data and instructions into the computer. A mouse is a small handheld device that contains at least one button. The mouse controls the movement of a symbol on the screen called a pointer. For example, as you move the mouse across a flat surface, the pointer on the screen also moves. With the mouse, you can make choices, initiate a process, and select objects. A microphone allows a user to speak to the computer to enter data and instructions into the computer. A scanner reads printed text and pictures and then translates the results into a form the computer can use. For example, you can scan a picture, and then include the picture when creating a brochure. With a digital camera, you can take pictures and transfer the photo graphed image to the computer, instead of storing the images on traditional film. A PC camera is a digital video camera attached to a computer. A PC camera allows home users to create a movie and take digital still photographs on their computer. With a PC camera, you also can have a video telephone call — where someone can see you while communicating with you. Output Devices An output device is any hardware component that can convey information to a user. Three commonly used output devices are a printer, a monitor, and speakers. A printer produces text and graphics on a physical medium such as paper or transparency film. A monitor, which looks like a television screen, displays text, graphics, and video information. Speakers allow you to hear music, voice, and other sounds generated by the computer. System Unit The system unit, sometimes called a chassis, is a box-like case made from metal or plastic that protects the internal electronic components of the computer from damage. The circuitry in the system unit usually is part of or is connected to a circuit board called the motherboard. Two main components on the motherboard are the central processing unit and memory. The central processing unit (CPU), also called a processor, is the electronic device that interprets and carries out the basic instructions that operate the computer. During processing, the processor places instructions to be executed and data needed by those instructions into memory. Memory is a temporary holding place for data and instructions. Both the processor and memory consist of chips. A chip is an electronic device that contains many microscopic pathways that carry electrical current. Chips, which usually are no bigger than one-half inch square, are packaged so they can be attached to a motherboard or other circuit board. Some computer components, such as the processor, memory, and most storage devices, are internal and reside inside the system unit. Other components, such as the key board, mouse, microphone, monitor, printer, scanner, digital camera, and PC camera, usually are located outside the system unit. These devices are considered external. A peripheral is any external device that attaches to the system unit. Storage Devices Storage holds data, instructions, and information for future use. Storage differs from memory, in that it can hold these items permanently. Memory, by contrast, holds items only temporarily while the processor interprets and executes instructions. A storage medium (media is the plural) is the physical material on which a computer keeps data, instructions, and information. A storage device records and retrieves items to and from a storage medium. Storage devices often function as a source of input because they transfer items from storage into memory. Common storage devices are a floppy disk drive, a Zip® drive, a hard disk drive, a CD-ROM drive, a CD-RW drive, a DVD-ROM drive, and a DVD+RW drive. A drive is a device that reads from and may write on a storage medium. This media includes floppy disks, Zip® disks, hard disks, and compact discs. A floppy disk consists of a thin, circular, flexible disk enclosed in rigid plastic. A floppy disk stores data, instructions, and information using magnetic patterns. You insert and remove a floppy disk into and from a floppy disk drive. A Zip® disk is a higher capacity disk that can store the equivalent of up to 170 standard floppy disks. A hard disk provides much greater storage capacity than a floppy disk. A hard disk usually consists of several circular platters that store items electronically. These disks are enclosed in an airtight, sealed case, which often is housed inside the system unit. Some hard disks are removable, which enables you to insert and remove the hard disk from a hard disk drive, much like a floppy disk. Removable disks are enclosed in plastic or metal cartridges so you can remove them from the drive. The advantage of removable media such as a floppy disk and removable hard disk is you can take the media out of the computer and transport or secure it. A compact disc is a flat, round, portable medium that stores data using microscopic pits, which are created by a laser light. One type of compact disc is a CD-ROM, which you can access using a CD-ROM drive. A Picture CD is a special type of CDROM that stores digital versions of photographs for consumers. A variation of the standard CD-ROM is the rewriteable CD, or CD-RW. In addition to accessing data, you also can erase and store data on a CD-RW. To use a CD-RW, you need a CD-RW drive. Another type of compact disc is a DVD-ROM, which has tremendous storage capacities — enough for a fulllength movie. To use a DVDROM, you need a DVD drive. A variation of the standard DYD-ROM is the rewriteable DYD, or DVD+RW. PC Cards and memory cards are popular types of miniature storage media. You then can transfer the items, such as the digital photographs, from the media to your computer using a device called a card reader. Communications Devices Communications devices enable computer users to communicate and to exchange items such as data, instructions, and information with another computer. A modem is a communications device that enables computers to communicate usually via telephone lines or cable. Modems are available as both external and internal devices. Communications devices, such as modems, allow you to establish a connection between two computers and transmit items over transmission media, such as cables, telephone lines, or satellites. INPUT DEVICES Keyboard devices Offline Data Preparation Methods Table 1 below illustrates the Data Preparation Devices with corresponding input devices and media. These methods need special data preparation devices. The term “Off linen is used because this activity is done outside the computer and before input. In Sri Lanka the punch card system was popular with the computers used from 1969 to the late 1970s. Later, it was replaced by Key-to-Diskette systems, which are still in use in Sri Lanka at a few places having high volume batch processing and less time critical applications such as: Data Processing of Public Examinations, Provident Fund applications, Census applications, Archival of high volume business documents etc. Input Media Input Devices Data Preparation Devices Punch Card Card Reader Key Punch & Verifier Machines Magnetic Tape Magnetic Tape Drive Key-To-Tape Encoder or Key-To-Disk System Magnetic diskette Diskette Reader / Drive Key-To-Diskette System Table I – The Data Preparation Systems Key Board Devices - On-line Terminals The more common types of terminals are: Visual Display Unit (VDU) or Video Terminal VDU has ‘a television’ type screen and a keyboard. Here, input is by a keyboard and output through display on Cathode Ray Tube (CRT). This is the most common method of input. General Features of a Video Terminal 01. It is an input/output (dual purpose) device. 02. The keyboard generally resembles a typewriter (QWERTY) keyboard, but there is a wide range of variations. 03. Display clarity (Resolution) depends on the pixel density. Pixel is the smallest display element to represent single color. Each character is formed by combination of pixels. 04. Standard screen display includes 24 rows by 80 column character matrix totaling 1920 characters. 05. Screen movement is generally; Line by line - Scrolling or page by page Paging. 06. Most of Video Terminals are ‘dumb’ terminals. New models appear now in the market includes microprocessor with various levels of facilities. Terminals A terminal is a form of input (and output) device that connects you to a mainframe or other type of computer called a host computer or server. There are four types of terminals: A dumb terminal can be used to input and receive data, but it cannot process data independently. It is used only to gain access to information from a computer. Such a terminal may be used by an airline reservations clerk to access a mainframe computer for flight information An intelligent terminal includes a processing unit, memory, and secondary storage such as a magnetic disk. Essentially, an intelligent terminal is a micro computer with communications software and a telephone hookup (modem) or other communications link. These connect the terminal to the larger computer or to the Internet. Microcomputers operating as intelligent terminals are widely used in organizations. A network terminal is also known as a thin client or network computer, is a low-cost alternative to an intelligent terminal. Most network terminals do not have a hard-disk drive and must rely on the host computer or server for application and system software. These devices are becoming increasingly popular in many organizations. An Internet terminal, also known as a Web terminal, provides access to the Internet and displays Web pages on a standard television set, these special purpose terminals have just recently been introduced to offer Internet access to people without microcomputers. Unlike the other types of terminals, Internet terminals are used almost exclusively in the home. A Point-of-Sale (POS) Terminal A Point-of-Sale (POS) Terminal is a smart terminal used very much like a cash register, but it also captures sales and inventory’s data at the point of sale and sends it to the central computer for processing. Many supermarkets have POS terminals that are connected directly to a central computer so that the sales data can be immediately terminal usually displays the and possibly the recorded. This type of price, the product number, product description. In terminal is equipped with keyboard, a cash drawer, and addition, this type of a cash-register-type a printer to print the receipt. It can operate on standalone basis and data stored can be transferred to the main computer by using a computer medium such as a diskette. Banking / Financial Transaction Terminal The most common terminals are: 01. Automatic Teller Machine (ATM) A special intelligent terminal located outside the bank for a customer to operate on his own to perform a limited number of banking transactions. e.g.: cash withdrawal, cash transfers, utility bill payment etc. 02. Teller Operator terminal This is a specialized dumb/smart terminal for the bank teller operators who work in the front office of a bank to handle customer transactions. 03. Normal Video Terminals Portable Terminal It is consists of a Key Board, flat screen monitor and built in communication software/hardware which can connect from a communication link to a remote location through a computer. The portability of light weight. There are a wide (e.g.: Terminal for traveling salesman.) the terminal is due to its range of products available. Non Keyboard Devices Mouse The mouse is one of the devices connected to the computer by a small cable. As the mouse is rolled across the desktop, the cursor moves across the screen. When the cursor reaches the desired location, the user usually pushes button on the mouse once or or a command to the often used with graphicsspecial software for twice to signal a menu selection computer. Mouse technology is oriented personal computers. With graphics, the mouse can be used to create figures and patterns like a pen or a Paint Brush directly on the video display screen. e.g.: use with Corel Draw or Howard Graphics, Desk Top Publishing Applications etc. Joystick It is a device which contains lever which can be used to move objects on the screen. e.g.: It is normally used to play computer games. Light Pen The light pen is a special attachment to a graphics terminal. The pen is touched on the video display screen switched on, and then you can Light pens are frequently and drafting engineers. Of at the desired location and draw the image on the screen. used by graphic designers, illustrators, course, data may also be entered using keyboard e.g. Computer Aided Design (CAD), Architectural applications etc. Touch Screen Limited amounts of data can be entered via a terminal or a microcomputer that has a touches the screen at the labeled boxes, to point out” Inquiry Terminals for touch screen. The user simply by desired locations, marked choices to the computer. e.g.: general public such as Terminals located in the lobby areas of a large building complex. This will enable users to operate without much technical knowledge & skill. Scanning Devices Scanners A Digital Scanner translates images such as pictures or documents into digital form. This is one area development A wide has variety been of where substantial research & taking place in the recent past. products are now available in the products are: marketplace. The most common Hand Held Scanner Used mostly with small Publishing) systems to input pictures, scale publishing (Desk Top logos etc. Flat Bed Scanner Used to input text without images. Special available to process these editing, merging etc. based documents with or software packages are now text based images such as Character Scanners These are hand held devices which can read data printed in special type fonts (e.g.: OCR) or hand written data based on recommended guidelines. In addition, there are Optical Character Readers which operate at high speed to handle high volume batch oriented input like Electricity billing meter readings. Optical Character Recognition (OCR) Optical character recognition is a device that is used to scan the text, which is found on a document, and then the data is converted into electrical signals for the computer. This device can be used to read a special type of font. However, the more expensive OCR devices can read a variety of fonts; some can even read hand written documents. Optical Mark Recognition (OMR) The input device is Optical Mark Reader. In some of the foreign examinations like SAT or TOEFL the candidate application forms as well as the answer sheets are specially designed (Mark Sense Cards) to record data by using pencil marks. Open University of Sri Lanka and University of Colombo BIT program also use a similar method. Data recorded in this form is converted into computer-usable form by an Optical Mark Reader (OMR). The OMR device has a high-intensity light inside which is directed in the form of a beam at the sheet of paper being fed through it. The beam scans the marked forms and detects the number and location of the pencil marks. The data is then converted into electrical signals for the computer. OMRs come in a variety of sizes and shapes that depend on the size of the forms to be read and the required loading and processing capacity of the reader. Magnetic-Ink Character Recognition (MICR) This is specially designed for the input of high volume cheques in the banking industry. The advantages of the MICR system are that Human involvement is minimum, thus the potential for errors is small, The codes can be read by both people and machines, It is fast, automatic, and reliable (2400 checks/mm). The cheque leaf taken into the machine, and magnetize the ferric particles present in the data printed at the bottom edge of it. At the first read station it recognizes data based on magnetic induction & converts into electrical signals. Generally at the second read station it reads again & compare with the first reading for accuracy. In addition to reading, it sort the cheque leaves in a bundle according to the bank code & output to respective pigeon holes. e.g.; Cheque Clearing House of Sri Lanka. Bar Code Reader Bar Code is a collection of thick and thin lines and spaces that represent data in binary. E.g.: • Parcel tracking system in courier companies • File tracking system in an office • Issue of items in a supermarket. • Record the movement of books in a library In courier application the parcel reference number is bar coded & recorded in all relevant documents & the parcel it. This reference number is input to the computer system by using a portable barcode scanner or wand reader. The wand has a scanning device that analyzes light & dark bars for width & spacing. This wand reader is a special attachment to a video terminal. Card Reading Devices Time/Punch Card IBM made the punch-card technology into the business standard of the 1950's and 1960's. There are manual punch card readers available. But now a day this technology is not using widely. Voice and Image Input Devices Microphone A microphone wants and to take varying into pressure waves in the air varying electrical signals. technologies conversion: commonly convert them There are five different used to accomplish this Carbon microphones The oldest and simplest microphone uses carbon dust. This is the technology used in the first telephones and is still used in some telephones today. The carbon dust has a thin metal or plastic diaphragm on one side. As sound waves hit the diaphragm, they compress the carbon dust, which changes its resistance. By running a current through the carbon, the changing resistance changes the amount of current that flows. Dynamic microphones A dynamic microphone takes advantage of electromagnet effects. When a magnet moves past a wire (or coil of wire), the magnet induces current to flow in the wire. In a dynamic microphone, the diaphragm moves either a magnet or a coil when sound waves hit the diaphragm, and the movement creates a small current. Ribbon microphones - In a ribbon microphone, a thin ribbon is suspended in a magnetic field. Sound waves move the ribbon which changes the current flowing through it. Condenser microphones A condenser microphone is essentially a capacitor, with one plate of the capacitor moving in response to sound waves. The movement changes the capacitance of the capacitor, and these changes are amplified to create a measurable signal. Condenser microphones usually need a small battery to provide a voltage across the capacitor. Crystal microphones Certain crystals change their electrical properties as they change. By attaching a diaphragm to a crystal, the crystal will create a signal when sound waves hit the diaphragm. Web Camera A cam, home cam, or Webcam is a video camera, usually attached directly to a computer, whose current or latest image is request able from a Web site. A live cam is one that is continually providing new images that are transmitted in rapid succession or, in some cases, in streaming video. Sites with live cams sometimes embed Cams have caught on; several thousand sites them as Java applets in Web pages. there are now (we estimate) with cams. The first cams on fish tanks and coffee today's live cams are on sex traffic information, and the were positioned mainly machines. Many of oriented sites. For travel promotion, remote visualization of any ongoing event that's interesting, webcams seem like an exciting possibility that will become more common as users get access to more bandwidth. OUTPUT DEVICES Monitors Mono (Monochrome) – Display a single Color. CGA - Color Graphic Adapter (4 Colors) EGA – Enhance Graphic Adapter (16 Colors) VGA – Video Gr. Ad. (16 colors & 256 shading) SVGA – Super VGA Printers Impact Printers The Print mechanism strikes against the paper. Non Impact Printers The Print mechanism does not strike against the ribbon or paper. Character Printers Speed in Characters per Second (CPS) Used for low to medium volume applications E.g.: Matrix, Ink Jet. Line Printers Speed in Lines per Minute (LPM) Used for high volume medium quality applications. E.g.: printing of public examination results. Page Printers Speed in Pages per Minute (PPM) Used for medium to high volume, high quality applications. E.g.: Print a master copy of a magazine by using a Laser Printer. Color Printers Color printers use a Color Cartridge. Time to time you have to place the cartridge when the cartridge is over. Black and White Printers Black and White Printers use a Black and White Cartridge. Time to time you have to place the cartridge when the cartridge is over. There are printers which supports both Color and Black and White cartridges. Text Printers To print text there are specially text printers. The quality is very low in these printers. Graphic Printers These are very high quality printers. These printers are expensive than normal printers. You can get very high quality Images printouts by using a graphic printer. Graphic designers and the people in studios use Graphic printers. Dot Matrix Printers The most widely used printer which prints one character at a time. The technology has improved during the recent past to include very high quality & reasonably fast printers. Daisy Wheel Printers A kind of impact printer where the characters are arranged on the ends of the spokes of a wheel (resembling the petals on a daisy). The wheel (usually made of plastic) is rotated to select the character to print and then an electrically operated hammer mechanism bends the selected spoke forward slightly, sandwiching an ink ribbon between the character and the paper, as in a typewriter. One advantage of this arrangement over that of a typewriter is that different wheels may be inserted to produce different typefaces. Inkjet Printers Ink printers work in much the same fashion as dot-matrix printers in that they form images or characters with little dots. the dots are formed, not by hammer like pins, tiny droplets of ink, and the text these printers However, but by produce is of letter quality. These printers can almost match the speed of dot- matrix printers - up to about 270 eps-and they produce less noise. Thermal Printers Thermal printers use heat to produce an image on special paper. The print mechanism - rather like a dot - matrix print head - is designed to heat the surface of chemically treated paper so that a dot is produced based on the reaction of the chemical to the heat. No ribbon or ink is involved. It can print multiple colors. Laser Printers Laser printer technology is much less mechanical than impact printers resulting in much higher speeds and quieter operation. The process resembles the operation of a photocopy machine. A laser beam is directed across the surface of a light-sensitive drum and fixed as needed to record an image in the form of a pattern of tiny dots. The image is then transferred to the paper. This printer prints a page at a time - in the same fashion as a copying machine, using a special toner. When high-speed laser printers (also called page printers) were introduced, they were very expensive. However, recent laser printer technology has made desktop versions available at very reasonable prices. Plotters A plotter is a specialized output device designed to produce high-quality graphics in a variety of colors. Drum plotters and flat bed plotters both use pens and electrostatic plotters do not. Drum Plotter The paper is mounted on the surface of a drum. The drum revolves and the plotter pens (which are similar to felt-tip pens) are horizontally positioned over the target area. When the paper has rotated to the correct point, the pens are dropped to the surface moved left and right under program control across the paper as the drum revolves. When the image is the pens are raised from the surface. complete, Flat Bed Plotter These are designed so that the paper is placed flat and one or more pens move horizontally and vertically across the paper. Electrostatic Plotters Use electrostatic charges to create images out of very small dots on specially treated paper. Electrostatic plotters are faster than pen plotters and can produce images of very high resolution, e.g.: Used by Architects, Surveyors, and Engineers. Voice Output Devices Voice output should be a more useful medium. This technology has had to overcome many hurdles. The most difficult has been that every individual perceives speech differently; that is, the voice patterns, pitches, and reflections we can hear and understand are different for all of us. It is not always easy to understand an unfamiliar voice pattern. At this point, two different approaches to voice output have evolved: Speech coding This relies on human speech as a reservoir of sounds to draw from in building the words and phrases to be output. Sounds are codified and stored on disk to be retrieved and translated back as sounds. Speech coding has been used in applications such as automobiles, toys, and games. Speech synthesis In this method voice is produced electronically without the use of a human voice. The largest application to date for the speech synthesis approach to voice output converting text into “spoken” words has many potential uses, including providing reading machines for the blind. And, of course, sound output does not have to be in voice form, it can be music or special-effects sounds, such as the sound accompaniment for computer animation, in cartoons etc. COM Devices Serial port or "com port". A connector on a computer to which you can attach a serial line connected to peripherals which communicate using a serial (bit-stream) protocol. The most common type of serial port is a 25-pin D-type connector carrying EIA-232 signals. Smaller connectors (e.g. 9-pin D-type) carrying a subset of EIA-232 are often used on personal computers. The serial port is usually connected to an integrated circuit called a UART which handles the conversion between serial and parallel data. In the days before bit-mapped displays, and today on multi-user systems, the serial port was used to connect one or more terminals (teletypewriters or VDUs), printers, modems and other serial peripherals. Two computers connected together via their serial ports, possibly via modems, can communicate using a protocol such as UUCP or CU or SLIP. CPU (CENTRAL PROCESSING UNIT) Processor A processor is the logic circuitry that responds to and processes the basic instructions that drive a computer. The term processor has generally replaced the term central processing unit (CPU). The processor in a personal computer or embedded in small devices is often called a microprocessor. Arithmetic and Logic Unit An arithmetic-logic unit (ALU) is the part of a computer processor (CPU) that carries out arithmetic and logic operations on the operands in computer instruction words. In some processors, the ALU is divided into two units, an arithmetic unit (AU) and a logic unit (LU). Some processors contain more than one AU - for example, one for fixed-point operations and another for floating-point operations. (In personal computers floating point operations are sometimes done by a floating point unit on a separate chip called a numeric coprocessor.) Typically, the ALU has direct input and output access to the processor controller, main memory (random access memory or RAM in a personal computer), and input/output devices. Inputs and outputs flow along an electronic path that is called a bus. The input consists of an instruction word (sometimes called a machine instruction word) that contains an operation code (sometimes called an "op code"), one or more operands, and sometimes a format code. The operation code tells the ALU what operation to perform and the operands are used in the operation. (For example, two operands might be added together or compared logically.) The format may be combined with the op code and tells, for example, whether this is a fixed-point or a floating-point instruction. The output consists of a result that is placed in a storage register and settings that indicate whether the operation was performed successfully. (If it isn't, some sort of status will be stored in a permanent place that is sometimes called the machine status word.) In general, the ALU includes storage places for input operands, operands that are being added, the accumulated result (stored in an accumulator), and shifted results. The flow of bits and the operations performed on them in the subunits of the ALU is controlled by gated circuits. The gates in these circuits are controlled by a sequence logic unit that uses a particular algorithm or sequence for each operation code. In the arithmetic unit, multiplication and division are done by a series of adding or subtracting and shifting operations. There are several ways to represent negative numbers. In the logic unit, one of 16 possible logic operations can be performed - such as comparing two operands and identifying where bits don't match. The design of the ALU is obviously a critical part of the processor and new approaches to speeding up instruction handling are continually being developed. Control Unit Control Unit controls every single hardware part attached to the computer. Its main task is controlling the hardware devices which are attached to the machine according to the signals of CPU. LOGICAL STRUCTURE OF A COMPUTER BACKING STORAGE INTERNAL STORAGE INPUT OUTPUT ARITHMETIC & LOGICAL UNIT. CONTROL UNIT HOW COMPUTERS WORK? Computers process information using the instructions from the user to produce the desired results. The instruction that you feed in the computer, through software, is the basic input. This input could be fed through a keyboard or a mouse or a scanner, etc. These instructions are then sent to the processor know as the central processing unit for processing. By processing, broadly we mean carrying out of instructions for a task to be completed. After the task or processing has been performed, the processor send, the result, know as the output to the screen or the printer, as desired by you want to store the information for any future use you can very well store it either on the hard disk or any other storage device like floppy disk etc. the illusion, that follows makes the whole procedure more clear. BOOTING PROCESS Booting the Computer The PC boot process starts when a small program within the BIOS chip looks for an active partition and loads the operating system. There are two methods for booting a computer: cold and warm booting. Cold Boot Cold booting occurs when the computer’s power switch is turned on. The effect of a cold boot is that it brings the system to the very beginning of the boot process, beginning with the POST. This may become necessary when the computer stops responding to any commands, including warm boots. Warm Boot A warm boot bypasses the first two system tests and goes directly to the bootstrap loader (the point where DOS loads). A warm boot is triggered by pressing the Ctrl, Alt, and Del keys at the same time. CTRL + ALT + DEL Rebooting the computer should be used only as a last resort. Any information in open application files could be lost when rebooting takes place. Creating Boot Disks Every once in a blue moon your system may refuse to boot. There are numerous reasons that could cause this. If you are prepared with an emergency boot disk for such an occasion, you will save yourself a lot of anxious moments The steps for preparing a boot disk are as follows: 1. Format a floppy disk using the IS switch. Put a blank diskette into your floppy drive. 2. 3. 4. Type format A: /S Copy the AUTOEXEC.BAT and CONFIG.SYS files to the newly /S-formatted disk. 5. Copy any files and drivers that are essential to the boot process such as IO.SYS, COMMAND.COM and other files necessary for your particular system. Label the disk appropriately and write protect it by flipping the black switch on the bottom of the diskette. Store the disk in a safe and readily accessible spot. By default, every time the computer is started, it searches in drive A for a bootable floppy disk. In the event that the hard drive does not boot, you are able to access the system from drive A. This allows you the opportunity to look for the problem. OPERATING SYSTEM Operating System Concepts Many of the first operating systems were device dependent and proprietary. A device dependent software product is one that runs only on a specific type or make of computer. Proprietary software is privately owned and limited to a specific vendor or computer model. When manufacturers introduced a new computer or model, they often produced an improved and different proprietary operating system. Problems arose, however, when a user wanted to switch computer models or manufacturers. The user’s application soft ware often would not work on the new computer because the applications were designed to work with a specific operating system. Some operating systems still are device dependent. The trend today, however, is toward device- independent operating systems that run on computers provided by a variety of manufacturers. The advantage of deviceindependent operating systems is you can retain existing application software and data files even if you change computer models or vendors. This feature generally represents a sizable savings in time and money. New versions of an operating system usually are downward compatible. A downward compatible operating system is one that recognizes and works with application software written for an earlier version of the operating system. The application software, by contrast, is said to be upward compatible. An upward- compatible product is written for an earlier version of the operating system, but also runs with the new version. The three basic categories of operating systems that exist today are stand-alone, network, and embedded. The table in Figure 8-18 lists names of operating systems in each category. The following pages discuss the operating systems listed in the table. Stand-Alone Operating Systems A stand-alone operating system is a complete operating system that works on a desktop or notebook computer. Some stand-alone operating systems, called client operating systems, also work in conjunction with a network operating system. That is, client operating systems can operate with or without a network. Examples of stand-alone operating systems are DOS, Windows 3.x, Windows 95, Windows NT Workstation, Windows 98, Windows 2000 Professional, Windows Millennium Edition, Windows XP Home Edition, Windows XP Professional Edition, Mac, OS X, OS/2 Warp Client, UNIX, and Linux. The following paragraphs briefly discuss most of these operating systems. The section that covers network operating systems discusses UNIX and Linux. Loading an Operating System The "boot" process comes from the term "boot strap". It is a play on the concept of pulling one's self up by one's own boot straps. What actually happens is that when the computer is powered up, the CPU runs the startup code implanted in the system's ROM BIOS (Read Only Memory Basic Input Output System). This startup program contains the code that tests the computer and sets up the hardware for use. Its last step is to load and run a program stored on the first sector of the first drive. This is the master boot record (MBR), and the program is the master boot program (MBP). The MBP looks to see where the primary partitions are and which one is set as the active partition. The active partition has its own boot record, and this contains a program designed to start the operating system located on that partition. A partition boot record is usually referred to as the partition root super block. Popular Operating Systems Stand-alone DOS Windows 3.x Windows 95 Windows NT Workstation Windows 98 Windows 2000 Professional Windows Millennium Edition Windows XP Home Edition Windows XP Professional Edition Mac OS X OS/2 Warp Client UNIX Linux Network Netware Windows NT Server Windows 2000 Server Windows.NET Server OS/2 Wrap Server for E-business UNIX Linux Solaris Embedded Windows CE Pocket PC 2002 Palm OS DOS (Disk Operating System) The term DOS (Disk Operating System) refers to several single user operating systems developed in the early 1980s for personal computers. The two more widely used versions of DOS were PC-DOS and MS-DOS. Microsoft Corporation developed both PC-DOS and MS-DOS. The functionality of these two operating systems was essentially the same. The basic difference between PC-DOS and MS-DOS was the type of computer on which they were installed. Microsoft developed PC-DOS (Personal Computer DOS) for IBM, which in turn installed and sold PC-DOS on its computers. At the same time, Microsoft marketed and sold MS-DOS (Microsoft DOS) to makers of IBM-compatible PCs. DOS used a command-line interface when Microsoft first developed it. Later versions included both command-line and menu-driven user interfaces, as well as improved memory and disk management. At its peak, DOS was a widely used operating system, with an estimated 70 million computers running it. Today, DOS no longer is widely used because it does not offer a graphical user interface (GUI) and it cannot take full advantage of modern 32-bit personal computer processors. Windows 98 Microsoft developed an upgrade to the Windows 95 operating system, called Windows 98. The Windows 98 operating system was more integrated with the Internet than Windows 95. For example, Windows 98 included Microsoft Internet Explorer, a popular Web browser. The Windows 98 file manager, called Windows Explorer, and also had a Web browser look and feel. With Windows 98, you could have an Active Desktop interface, which allowed you to set up Windows so icons on the desktop and file names in Windows Explorer worked similar to Web Links. Windows 98 also provided faster system startup and shutdown, better file management, and support for multimedia technologies such as DVD and WebTV™ (today known as MSN® TV). Windows 98 supported USB, so you easily could add and remove devices in your computer. Windows NT Windows NT Workstation Microsoft developed Windows NT Workstation as a client operating system that could connect to a Windows NT Server. Windows NT, also referred to as NT, was an operating system designed for client! Server networks. Windows NT Workstation had a Windows 95 interface. Thus, users familiar with Windows 95 easily could migrate to Windows NT Workstation. Businesses most often used Windows NT Workstation. Windows NT Server As previously mentioned, Microsoft developed Windows NT as an operating system for client/server networks. The server in this environment used Windows NT Server. The client computers used Windows NT Workstation or some other stand-alone version of Windows. Start and Login In order to get your computer to work you need both hardware and software. An operating system is software that you use in order to communicate with the computer’s hardware such as the mouse, the keyboard and the computer’s memory. Your computer must have the operating system software installed before you can perform any operations. The operating system automatically starts when you switch on the computer. The startup process is called booting. Most operating systems provide built-in security, which ensures that only authenticated users can access the computer. Thus whenever you start your computer you must provide your valid user name and password. This attempt is known as “logging on” and the entire process of verification is known as the “logon process”. This process helps to protect your documents from unauthorized users. 1. Switch on the computer (The “Welcome to Windows” screen will be displayed) 2. Press Ctrl+Alt+Delete to open the “Log On to Windows” dialog box 3. In the “User Name” box, enter your user name 4. In the “Password” box, enter your password 5. Click OK Use Mouse (Buttons) The mouse is an input device you can use to perform various tasks such as opening applications, selecting items, copying data, and moving data. The mouse moves on a flat surface, usually a mouse pad. As you move the mouse, a mouse pointer moves in the same direction on the screen. By default, the left mouse button is the primary mouse button. You use the left mouse button for selecting, moving and opening objects. If you are a left hander you may configure the right mouse button as the primary mouse button if you need to. The following table shows the mouse actions and how to perform them with the left mouse button as the primary button. Mouse Action How Point Click Double Place the mouse pointer over an object. Press and release the left mouse button. Click Press and release the left mouse button two times in rapid succession. Drag While holding down the left mouse button, move the pointer to your desired location, and then release the button. Right Click Press and release the right mouse button. Pointing Place the mouse pointer over an object Clicking Press and release the left mouse button. Dragging While holding down the left mouse button, move the pointer to your desired location, and then release the button. Use Keyboard (Special Keys for Windows) The key board is the most often used input device. There are some special keys on the keyboard that will allow you to perform some frequent tasks. Some of those are listed below. 1. The windows key: To open the start menu 2. Ctrl+Esc: To open the start menu 3. Ctrl+C: To copy a selected item 4. Ctrl+X: To cut a selected item 5. Ctrl+V: To paste a selected item 6. Ctrl+P: To print 7. The Caps Lock: To change case 8. Alt+F4: To close the current window/ Exit/ Shut Down Shutting Down Your Computer 1. Click on the Start Button 2. Select Shut Down 3. Select OK SYSTEM SOFTWARE Computer Software Software, also called a computer program or simply a program, is a series of instructions that tells the hardware of a computer what to do. Some instructions allow you to input data from the keyboard and direct the computer to store the data in memory. Other instructions cause data in memory to be used in calculations such as adding a series of numbers to obtain a total. Some instructions compare two values in memory and direct the computer to perform alternative operations based on the results of the comparison. Other instructions direct the computer to print a report, display information on the monitor, draw a color picture on the monitor, or store information on a disk. A computer carries out, or executes, the instructions in a pro gram by first placing, or loading, the instructions into the memory of the computer. Usually, the computer loads the instructions from storage into memory. For example, each time a program executes, it might load from the hard disk into memory. When you purchase a program, you typically receive media such as a CD-ROM(s) or a DYD-ROM that contains the software. Some programs can load into memory directly from the media. With other programs, you must install a part or all of the soft ware on the computer’s hard disk before you can use the program. Some programs also require you to insert the media, such as a CD-ROM, into the drive while you use, or run, the program. Others do not. This program requires a CD-ROM in the CD-ROM drive. When you buy a computer, it usually has some software pre installed on its hard disk. This enables you to use the computer as soon as you set it up. Software is the key to productive use of computers. With the proper software, a computer can become a valuable tool. The two categories of software are system software and application software. The following pages describe these categories of software. System Software System software consists of the programs that control the operations of the computer and its devices. System software serves as the interface between the user, the application software, and the computer’s hard ware. Two types of system software are the operating system and utility programs. Operating System An operating system (OS) is a set of programs containing instructions that coordinate all the activities among computer hardware devices. The operating system also contains instructions that allow you to run application software. Many of today’s computers use Microsoft’s most recent operating system, called Windows XP. When you start a computer, the operating system loads into memory from the computer’s hard disk. It remains in memory while the computer is running and allows you to communicate with the computer and other software. Utility Programs A utility program is a type of system soft ware that performs a specific task, usually related to managing a computer, its devices, or its programs. An example of a utility program is an uninstaller, which removes a program that has been installed on a computer. Most operating systems include several utility programs for managing disk drives, printers, and other devices. You also can buy stand-alone utility programs, which allow you to perform additional computer management functions. Language Translators The programs written by using a computer programming language should be converted to the machine code in order to run the program correctly and to get the wanted output. Computer programming languages are in human understandable for mat and machine code cannot be understood by human. Converting Human readable format computer programs in to machine readable format is done by Language Translators. Translators we can basically divide in to two parts called Compilers and Interpreters. The main difference between these two is the way that they convert the Computer programming language to machine language. Compiler A compiler is a special program that processes statements written in a particular programming language and turns them into machine language or "code" that a computer's processor uses. Typically, a programmer writes language statements in a language such as Pascal or C one line at a time using an editor. The file that is created contains what are called the source statements. The programmer then runs the appropriate language compiler, specifying the name of the file that contains the source statements. When executing (running), the compiler first parses (or analyzes) all of the language statements syntactically one after the other and then, in one or more successive stages or "passes", builds the output code, making sure that statements that refer to other statements are referred to correctly in the final code. Traditionally, the output of the compilation has been called object code or sometimes an object module. (Note that the term "object" here is not related to object-oriented programming.) The object code is machine code that the processor can process or "execute" one instruction at a time. More recently, the Java programming language, a language used in object-oriented programming, has introduced the possibility of compiling output (called byte code) that can run on any computer system platform for which a Java virtual machine or byte code interpreter is provided to convert the bytecode into instructions that can be executed by the actual hardware processor. Using this virtual machine, the bytecode can optionally be recompiled at the execution platform by a just-intime compiler. Traditionally in some operating systems, an additional step was required after compilation - that of resolving the relative location of instructions and data when more than one object module was to be run at the same time and they cross-referred to each other's instruction sequences or data. This process was sometimes called linkage editing and the output known as a load module. A compiler works with what are sometimes called 3GL and higher-level languages . An assembler works on programs written using a processor's assembler language. Interpreter An interpreter is a computer program that executes other programs. This is in contrast to a compiler which does not execute its input program (the source code) but translates it into executable machine code (also called object code) which is output to a file for later execution. It may be possible to execute the same source code either directly by an interpreter or by compiling it and then executing the machine code produced. It takes longer to run a program under an interpreter than to run the compiled code but it can take less time to interpret it than the total required to compile and run it. This is especially important when prototyping and testing code when an editinterpret-debug cycle can often be much shorter than an editcompile-run-debug cycle. Interpreting code is slower than running the compiled code because the interpreter must analyze each statement in the program each time it is executed and then perform the desired action whereas the compiled code just performs the action. This run-time analysis is known as "interpretive overhead". Access to variables is also slower in an interpreter because the mapping of identifiers to storage locations must be done repeatedly at run-time rather than at compile time. DBMS Software A database is a collection of data organized in a manner that allows access, retrieval, and use of that data. In a manual database, you might record data on paper and store it in a filing cabinet. With a computerized database, the computer stores the data in an electronic format on a storage medium such as a floppy disk or hard disk. Database software, also called a database management system (DBMS), is software that allows you to create, access, and manage a database. Using database software, you can add, change, and delete data in the database; sort and retrieve data from the database; and create forms and reports using the data in the database. APPLICATION SOFTWARE Application Software Application software consists of programs that perform specific tasks for users. Popular application software includes word processing software, spreadsheet software, data base software, and presentation graphics software. Word processing software allows you to create documents such as letters, memorandums, and brochures. Spreadsheet software allows you to calculate numbers arranged in rows and columns. Users perform financial tasks such as budgeting and forecasting with spreadsheet software. Database soft ware allows you to store data in an organized fashion, as well as retrieve, manipulate, and display that data in a variety of formats. With presentation graphics software, you create documents called slides that add visual appeal to presentations. Software vendors often bundle and sell these four applications together as a single unit. This bundle, called a suite, costs much less than if you purchased the applications individually. Microsoft’s Office XP is a very popular suite. Many other types of application software exist that enable users to perform a variety of tasks. Some widely used applications include the following: reference, education, and entertainment; desktop publishing; photo and video editing; multimedia authoring; network, communications, electronic mail (e-mail), and Web browsers; accounting; project management; and personal information management. Application software is available in a variety of forms: packaged, custom, freeware, public domain, shareware, and from application service providers. Word Processing Microsoft Word Corel WordPerfect Lotus Word Pro Microsoft Pocket Word Spread Sheet Microsoft Excel Corel Quattro Pro Lotus 123 Microsoft Pocket Excel Database Microsoft Access Corel Paradox Lotus Approach Microsoft Visual FoxPro Oracle Presentation Graphics Microsoft PowerPoint Corel Presentations Lotus Freelance Graphics Personal Information Manager Microsoft Outlook Corel CENTRAL Lotus Organizer Palm Multi Mail Software Suite Microsoft Office Corel WordPerfect Office Lotus SmartSuite Project Management Microsoft Project Primavera Sure Track Project Manager Accounting Intuit QuickBooks Peachtree Col11plete Accounting Tally Application Packages Copyrighted application or system software that meets the needs of a wide variety of users, not just a single user or company, is called packaged software. You can purchase packaged software from stores that sell computer products. You also can purchase packaged software from companies on the Internet. Custom-Made Software Sometimes a user or company with unique soft ware requirements cannot find packaged software that meets all its needs. In this case, the person or company can opt for custom software. Custom software, written by a programmer, is a tailor-made application or system program developed at a user’s request to perform specific functions. Freeware in Public-Domain Software and Shareware Freeware is application or system software provided at no cost to a user by an individual or a company. Freeware is copyrighted. You cannot resell it as your own. Public- domain software also is free software, but it has been donated for public use and has no copyright restrictions. Shareware is copyrighted software that is distributed free for a trial period. If you want to use a shareware program beyond that period, you send a payment to the person or company that developed the program. Companies that develop shareware rely on the honor system. The company trusts you to send payment if you continue to use the software beyond the stated trial period. Upon sending this small fee, the developer registers you to receive service assistance and updates. Examples of shareware, freeware, and public-domain software include utility programs, graphics programs, and games. Thousands of these pro grams are available on the Internet to download, or copy to your computer. You also can obtain copies of these programs from the developer, a coworker, or a friend. Application Service Provider Storing and maintaining programs can be a costly investment for individuals and businesses. Some opt to use an application service provider for their software needs. An application service provider (ASP) is a third-party company that manages and distributes software and services on the Internet. That is, instead of installing the software on your computer, you run the programs from the Internet. Some vendors pro vide access to the software at no cost. Others charge for use of the program. INTRODUCTION TO COMPUTER VIRUSES A virus is a piece of programming code usually disguised as something else that causes some unexpected and usually undesirable event. A virus is often designed so that it is automatically spread to other computer users. Viruses can be transmitted as attachments to an e-mail note, as downloads, or be present on a diskette or CD. The source of the e-mail note, downloaded file, or diskette you've received is often unaware of the virus. Some viruses wreak their effect as soon as their code is executed; other viruses lie dormant until circumstances cause their code to be executed by the computer. Some viruses are playful in intent and effect ("Happy Birthday, Ludwig!") and some can be quite harmful, erasing data or causing your hard disk to require reformatting. Generally, there are three main classes of viruses: Boot Sector These viruses infect executable code found in certain system areas on a disk. They attach to the DOS boot sector on diskettes or the Master Boot Record on hard disks. A typical scenario (familiar to the author) is to receive a diskette from an innocent source that contains a boot disk virus. When your operating system is running, files on the diskette can be read without triggering the boot disk virus. However, if you leave the diskette in the drive, and then turn the computer off or reload the operating system, the computer will look first in your A drive, find the diskette with its boot disk virus, load it, and make it temporarily impossible to use your hard disk. (Allow several days for recovery.) This is why you should make sure you have a bootable floppy. File Some file infector viruses attach themselves to program files, usually selected .COM or .EXE files. Some can infect any program for which execution is requested, including .SYS, .OVL, .PRG, and .MNU files. When the program is loaded, the virus is loaded as well. Other file infector viruses arrive as wholly-contained programs or scripts sent as an attachment to an email note. Trojan Horse Trojan horse attacks pose one of the most serious threats to computer security. If you were referred here, you may have not only been attacked but may also be attacking others unknowingly. This page will teach you how to avoid falling prey to them, and how to repair the damage if you already did. According to legend, the Greeks won the Trojan war by hiding in a huge, hollow wooden horse to sneak into the fortified city of Troy. In today's computer world, a Trojan horse is defined as a "malicious, security-breaking program that is disguised as something benign". For example, you download what appears to be a movie or music file, but when you click on it, you unleash a dangerous program that erases your disk, sends your credit card numbers and passwords to a stranger, or lets that stranger hijack your computer to commit illegal denial of service attacks like those that have virtually crippled the DALnet IRC network for months on end. The following general information applies to all operating systems, but by far most of the damage is done to/with Windows users due to its vast popularity and many weaknesses. (Note: Many people use terms like Trojan horse, virus, worm, hacking and cracking all interchangeably, but they really don't mean the same thing. If you're curious, here's a quick primer defining and distinguishing them. Let's just say that once you are "infected", Trojans are just as dangerous as viruses and can spread to hurt others just as easily!) Methods of Activation You can open a file by double clicking on it, but you can’t see the behind process. Most of the times these files can be .exe files which are in floppy diskettes or in Compact Disks. You might have down load something from the internet which you don’t trust 100%. You might open Email attachments without knowing. Virus Effects If your computer is running down slowly more than earlier. If the machine shut downs abnormally. If you can see unknown files or folders have been saved in to the hard disk. If anything abnormally happens in your machine than earlier it might be to a virus effect. Preventive Steps 1. Above all check every data medium you get. Even if it belongs to your best friend, it does not give you the guarantee of security. It concerns not only floppy disks, but also CD-ROMs, CD-RWs and ZIPs. Do not even open floppy disk if you get it from an unknown person. Every data medium obtained from an anonymous source is potentially infected. 2. Block the possibility of system boot from a floppy disk. Most of the latest BIOSes have a function, which enables to do it. In that simple way you can avoid the risk of having your computer infected by boot-sector viruses. 3. Do not open any letter with attached files received from an unknown sender. 4. Do not run macros in documents of office packages if an anti-virus monitor is off. 5. Use an anti-virus monitor working constantly at the background. For the best security the monitor should check the incoming mail and every file downloaded from the Internet. 6. You should systematically update definitions of viruses used by anti-virus software. Updating should be done at least once a month (the best once a week). 7. In a situation when you chat in the Internet (especially using mIRC) you have to follow the same rules as in case of received e-mails. Do not open any received files, if you do know who sent it to you and why. Some viruses are sent automatically, so same information about sender does not give you guarantee of security. 8. NEVER download blindly from people or sites which you aren't 100% sure about. In other words, as the old saying goes, don't accept candy from strangers. If you do a lot of file downloading, it's often just a matter of time before you fall victim to a Trojan. 9. Even if the file comes from a friend, you still must be sure what the file is before opening it, because many trojans will automatically try to spread themselves to friends in an email address book or on an IRC channel. There is seldom reason for a friend to send you a file that you didn't ask for. When in doubt, ask them first, and scan the attachment with a fully updated antivirus program. 10. Beware of hidden file extensions! Windows by default hides the last extension of a file, so that innocuous-looking "susie.jpg" might really be "susie.jpg.exe" - an executable Trojan! To reduce the chances of being tricked, unhide those pesky extensions. 11. NEVER use features in your programs that automatically get or preview files. Those features may seem convenient, but they let anybody send you anything which is extremely reckless. For example, never turn on "auto DCC get" in mIRC, instead ALWAYS screen every single file you get manually. Likewise, disable the preview mode in Outlook and other email programs. 12. Never blindly type commands that others tell you to type, or go to web addresses mentioned by strangers, or run pre-fabricated programs or scripts (not even popular ones). If you do so, you potentially trust a stranger with control over your computer, which can lead to Trojan infection or other serious harm. 13. Don't be lulled into a false sense of security just because you run anti-virus programs. Those do not protect perfectly against many viruses and trojans, even when fully up to date. Anti-virus programs should not be your front line of security, but instead they serve as a backup in case something sneaks onto your computer. 14. Finally, don't download an executable program just to "check it out" - if it's a Trojan, the first time you run it, you're already infected! Introduction to Anti-virus Software Antivirus (or "anti-virus") software is a class of program that searches your hard drive and floppy disks for any known or potential viruses. The market for this kind of program has expanded because of Internet growth and the increasing use of the Internet by businesses concerned about protecting their computer assets. Following are some URLs where you can find more information about antivirus software. International Computer Security Association http://www.icsa.net Virus Bulletin http://www.virusbtn.com Dr Salomon's page http://www.drsalomon.com CERT - Computer Emergency Response Team http://www.cert.org McAfee anti-virus http://vil.mcafee.com Symantec http://www.symantec.com/avcenter/ Other pages about virus: http://www.mks.com.pl http://www.antywirusy.pl http://www.wirusy.pl http://www.wirusy.onet.pl http://www.viruslist.com Norton Antivirus software by Symantec that scans and cleans instant-message attachments as well as email messages, and removes them automatically. You can download 15 day trial version freely from the Symantec website. McAfee Anti-virus software by MacAfee Co. Scan and restores your PC immediately. Detects Spy ware, blocks worms/unsafe scripts. Virus Checking Once you install the Virus guard it will automatically scan your system. When you boot up the machine and until you shut down the system it will be scanning your system behind other processes. When you insert a unknown floppy diskette its better to scan the diskette for viruses. You can right click on the floppy drive and select scan for viruses or open the anti virus program and select scan and then select floppy diskette. Then it will remove the infected files from the particular files and if it is not possible it asks to delete the infected files. It’s better to delete the infected files permanently if the recovery is not possible. Disinfection Computer viruses can be stored on floppy disks, hard disks, and even in the memory of a computer. Viruses frequently move from one computer to another on floppy disks or via files attached to email messages. Most viruses can be detected and removed using virus detection software such as McAfee VirusScan. In Nebula, we configure this package to be loaded at startup and watch for any signs of viruses. If Mc Afee VirusScan detects a virus in a file you're working with, it will notify you and give you some basic instructions on what to do next. You can also check the list below for instructions on dealing with some of the more pervasive virus infections. If you get a virus, you should always notify the person who gave you the file, by telephone if possible, so they can get rid of it on their computer, too. What you need to know • Any email claiming to be a Microsoft update is actually a virus itself; delete the file and do not click on any attachment(s). • Any email from another person claiming that you have a virus is most probably a virus hoax (see the Nebula virus hoax page for more information). • Do not delete files from your system based on an email message; check the hoax page for more information. • The most reliable source of information about a virus infection will come from your computer's McAfee program. If this tells you that you have a virus, do notify Nebula Support. • Do not open unknown attachments, ever. Immunization Viruses remain a significant threat to modern networked computer systems. Despite the best efforts of those who develop anti-virus systems, new viruses and new types of virus that are not dealt with by existing protection schemes appear regularly. In addition, the rate at which a virus can spread has risen dramatically with the increase in connectivity. Defenses against infections by known viruses rely at present on immunization yet, for a variety of reasons, immunization is often only effective on a subset of the nodes in a network and many nodes remain unprotected. Little is known about either the way in which a viral infection proceeds in general or the way that immunization affects the infection process. We present the results of a simulation study of the way in which virus infections propagate through certain types of network and of the effect that partial immunization has on the infection. The key result is that relatively low levels of immunization can slow an infection significantly. Removing If you are not sure if your computer is virus-free, try removing a virus from the hard disk as described below. 1. Shut down your machine, then start it up and log in; this ensures you have the latest virus update files on your system. 2. Choose Start - Programs - Network Associates - Virus Scan to begin a virus scan on your computer. 3. In the box labeled "Scan in", make sure the drive you wish to search for viruses is selected, typically C: If it isn't, click "Browse" and choose the right drive (and folder, if desired). Do not scan the I:\groups or H: drives; they are scanned regularly by the engineers. 4. Note that the "Include subfolders" checkbox should be selected, so Virus Scan looks through all subdirectories of the location you've chosen. 5. Note also that by default only program files are scanned; this includes Word and Excel document files. If you wish to scan all files, click the "All files" radio button. 6. Click "Scan Now" to start the search. 7. If a virus is found, click on the file name and choose Clean Infected Files. 8. If Virus Scan reports that it cannot clean a file, close the box and restart your computer. Then repeat the scan. If Virus Scan repeats the report, contact Nebula Support. If possible, use the Nebula Support icon on your desktop; this will include other information about your system that may help to solve the problem. 9. Remember, don't respond to an email telling you that you have a virus. It's either a hoax (in which case you just get more spam now that they know your address is valid), or a response to an infected message that only looks like it came from you--the latest viruses disguise their "From" addresses. Creation of a Rescue Disk We can call rescue disk as a boot disk. Rescue disk or Boot disk can be used in a situation where the computer does not boot in the normal way. This abnormal condition is can be due to a virus effect. You can follow the following instructions to create a boot disk in Windows XP. • • • • • • Insert a 3 ½’ floppy diskette in to your machine. Double Click on My Computer Icon on the desktop. Right Click on Floppy Diskette Drive. Select Format Select Create MSDOS Startup Disk Click on Start to create the Disk. Installing Anti-virus Software To install the antivirus soft ware first you have to buy a CD or download it from a website. As an example we’ll see how to install Norton Antivirus. First you select the setup file and double click on it. Then it will prompt you: You have to click on Yes and then it will start to scan all the files in your machine. It will scan all the files and if there is any virus infected file it will show you. When the scanning is complete it will show you a report. Then the setup will continue to install the software. After clicking Next button you have to read the software license agreement and accept the agreement to proceed. If you don’t accept the agreement setup will stop. Then it will ask for the path of the destination folder where the software files will be saved. After selecting the correct path and folder it will show you where the software will be installed. To proceed and install the software to your system you have to click on the Next button. Then you can see the progress of the installation. After coping the installation files in to your hard drive it will show you the Read me text file. The Readme.txt file contains the details about the product. Click Next to proceed. You will get this message if the setup has been successfully installed. Click on Finish to finish installing the software. After you install the software you have to register the product. We are going to use the trial version. If you want you can purchase the product online, or if you have already purchased you have to enter the product key which you will receive after purchasing the original product. Then it will display you a summary of tasks which the software will operate on. You can do wanted modifications. Click on Finish to finish the configuration. Upgrading Anti-virus Software Once you install the antivirus software it’s a must that you upgrade the software frequently. You can do it online. If your antivirus is not up to date then it will show you the following message. After upgrading the automatic System Scan will run. If you want you can stop the scan now and do it later. After the scan it will give you a summary. You can see whether the system scan is running in the background and its configuration. Uninstalling Anti-virus Software If you feel that you need better antivirus software you can uninstall the current antivirus software and install a new one. We’ll see how to uninstall the current antivirus software. You can go to the control panel and select Add/Remove Programs. Then select Norton antivirus 2004 and click on Remove. Then it will display: You can click on Remove All. Then it will warn you that this will remove antivirus software from your system. You have to click on Next to proceed. Then you can see the uninstallation progress. After finishing the uninstallation it will ask to restart the machine. You can select any option and click on Finish to finish the uninstallation. PRIMARY STORAGE RAM RAM (random access memory) is the place in a computer where the operating system, application programs, and data in current use are kept so that they can be quickly reached by the computer's processor. RAM is much faster to read from and write to than the other kinds of storage in a computer, the hard disk, floppy disk, and CD-ROM. However, there only as long as your computer is turn the computer off, RAM loses turn your computer on again, and other files are once usually from your the data in RAM stays running. When you its data. When you your operating system again loaded into RAM, hard disk. be compared to a person's short-term hard disk to the long-term memory. The memory focuses on work at hand, but can in view at one time. If short-term memory fills up, RAM can memory and the short-term only keep so many facts your brain sometimes is able to refresh it from facts stored in long-term memory. A computer also works this way. If RAM fills up, the processor needs to continually go to the hard disk to overlay old data in RAM with new, slowing down the computer's operation. Unlike the hard disk which can become completely full of data so that it won’t accept any more, RAM ever runs out of memory. It keeps operating, but much more slowly than you may want it to. How Big is RAM? RAM is small, both in physical size (it's stored in microchips) and in the amount of data it can hold. It's much smaller than your hard disk. A typical computer may come with 256 million bytes of RAM and a hard disk that can hold 40 billion comes in the form (meaning microchips and bytes. of RAM "discrete" separate) also in the form plug into holes motherboard. through a bus or processor. The hard drive, data on a magnetized of modules that in the computer's These holes connect set of electrical paths to the on the other hand, stores surface that looks like a phonograph record. Most personal computers are designed to allow you to add additional RAM modules up to a certain limit. Having more RAM in your computer reduces the number of times that the computer processor has to read data in from your hard disk, an operation that takes much longer than reading data from RAM. (RAM access time is in nanoseconds; hard disk access time is in milliseconds.) Why Random Access? RAM is called "random access" because any storage location can be accessed directly. Originally, the term distinguished regular core memory from offline memory, usually on magnetic tape in which an item of data could only be accessed by starting from the beginning of the tape and finding an address sequentially. Perhaps it should have been called "inconsequential memory" because RAM access is hardly random. RAM is organized and controlled in a way that enables data to be stored and retrieved directly to specific locations. A term IBM has preferred is direct access storage or memory. Note that other forms of storage such as the hard disk and CDROM are also accessed directly (or "randomly") but the term random access is not applied to these forms of storage. In addition to disk, floppy disk, and CD-ROM storage, another important form of storage is read-only memory (ROM), a more expensive kind of memory that retains data even when the computer is turned off. Every computer comes with a small amount of ROM that holds just enough programming so that the operating system can be loaded into RAM each time the computer is turned on. ROM ROM is "built-in" computer memory containing data that normally can only be read, not written to. ROM contains the programming that allows your computer to be "booted up" or regenerated each time you turn it on. Unlike a computer's random access memory (RAM), the data in ROM is not lost when the computer power is turned off. The ROM is sustained by a small long-life battery in your computer. If you ever do the hardware setup procedure with your computer, you effectively will be writing to ROM. PROM Programmable read-only memory (PROM) is read-only memory (ROM) that can be modified once by a user. PROM is a way of allowing a user to tailor a microcode program using a special machine called a PROM programmer. This machine supplies an electrical current to specific cells in the ROM that effectively blows a fuse in them. The process is known as burning the PROM. Since this process leaves no margin for error, most ROM chips designed to be modified by users use erasable programmable read-only memory (EPROM) or electrically erasable programmable read-only memory (EEPROM). EPROM EPROM (erasable programmable read-only memory) is programmable read-only memory (programmable ROM) that can be erased and re-used. Erasure is caused by shining an intense ultraviolet light through a window that is designed into the memory chip. (Although ordinary room lighting does not contain enough ultraviolet light to cause erasure, bright sunlight can cause erasure. For this reason, the window is usually covered with a label when not installed in the computer.) A different approach to a modifiable ROM is electrically erasable programmable read-only memory (EEPROM). EEPROM EEPROM (electrically erasable programmable read-only memory) is user-modifiable read-only memory (ROM) that can be erased and reprogrammed (written to) repeatedly through the application of higher than normal electrical voltage. Unlike EPROM chips, EEPROMs do not need to be removed from the computer to be modified. However, an EEPROM chip has to be erased and reprogrammed in its entirety, not selectively. It also has a limited life - that is, the number of times it can be reprogrammed is limited to tens or hundreds of thousands of times. In an EEPROM that is frequently reprogrammed while the computer is in use, the life of the EEPROM can be an important design consideration. A special form of EEPROM is flash memory, which uses normal PC voltages for erasure and reprogramming. Cache A cache (pronounced CASH) is a place to store something temporarily. The files you automatically request by looking at a Web page are stored on your hard disk in a cache subdirectory under the directory for your browser (for example, Internet Explorer). When you return to a page you've recently looked at, the browser can get it from the cache rather than the original server, saving you time and the network the burden of some additional traffic. You can usually vary the size of your cache, depending on your particular browser. Computers include caches at several levels of operation, including cache memory and a disk cache. Caching can also be implemented for Internet content by distributing it to multiple servers that are periodically refreshed. (The use of the term in this context is closely related to the general concept of a distributed information base.) Altogether, we are aware of these types of caches: • International, national, regional, organizational and other "macro" caches to which highly popular information can be distributed and periodically updated and from which most users would obtain information. • Local server caches (for example, corporate LAN servers or access provider servers that cache frequently accessed files). This is similar to the previous idea, except that the decision of what data to cache may be entirely local. • Your Web browser's cache, which contains the most recent Web files that you have downloaded and which is physically located on your hard disk (and possibly some of the following caches at any moment in time) • A disk cache (either a reserved area of RAM or a special hard disk cache) where a copy of the most recently accessed data and adjacent (most likely to be accessed) data is stored for fast access. • RAM itself, which can be viewed as a cache for data that is initially loaded in from the hard disk (or other I/O storage systems). • L2 cache memory, which is on a separate chip from the microprocessor but faster to access than regular RAM. • L1 cache memory on the same chip as the microprocessor. SECONDARY STORAGE Secondary storage is all addressable data storage that is not currently in the computer's main storage or memory. Synonyms are external storage and auxiliary storage. Floppy Disks A diskette is a random access, removable data storage medium that can be used with personal computers. The term usually refers to the magnetic medium housed in a rigid plastic cartridge and about 2 millimeters thick. "3.5-inch diskette," it can store megabytes (MB) of data. personal computers inch diskette drive computers desktop measuring 3.5 inches square Also up Although called to a 1.44 many today come with a 3.5preinstalled, and some notebook administered centrally- computers omit them. provide drives for magnetic diskettes Some older computers that are 5.25 inches square, about 1 millimeter thick, and capable of holding 1.2 megabytes of data. These were sometimes called "floppy disks" or "floppies" because their housings are flexible. In recent years, 5.25-inch diskettes have been largely replaced by 3.5-inch diskettes, which are physically more rugged. Many people also call the newer hard cased diskette a "floppy." Magnetic diskettes are convenient for storing individual files and small programs. However, the magneto-optical (MO) disk is more popular for mass storage, backup, and archiving. An MO diskette is only a little larger, physically, than a conventional 3.5-inch magnetic diskette. But because of the sophisticated read/write technology, the MO diskette can store many times more data. Disk Drives Hard Disks A hard disk is part of a unit, often called a "disk drive," "hard drive," or "hard disk drive," that store and provides relatively quick access to large amounts of data on an electromagnetically charged surface or set of surfaces. Today's computers typically come with a hard disk that contains several billion bytes (gigabytes) of storage. A hard disk is really a set of stacked "disks," each of which, like phonograph records, has data recorded electromagnetically in concentric circles or "tracks" on the disk. A "head" (something like a phonograph arm but in a relatively fixed position) records (writes) or reads the information on the tracks. Two heads, one on each side of a disk, read or write the data as the disk spins. Each read or write operation requires that data be located, which is an operation called a "seek." (Data already in a disk cache, however, will be located more quickly.) A hard disk/drive unit comes with a set rotation speed varying from 4500 to 7200 rpm. Disk access time is measured in milliseconds. Although the physical location can be identified with cylinder, track, and sector locations, these are actually mapped to a logical block address (LBA) that works with the larger address range on today's hard disks. Top view of a 36 GB, 10,000 RPM, IBM SCSI server hard disk, with its top cover removed. Note the height of the drive and the 10 stacked platters. (The IBM Ultra star 36ZX.) Optical Disks An optical disc is an electronic data storage medium that can be written to and read using a low-powered laser beam. Originally developed in the late 1960s, the first optical disc, created stored data as micron-wide A laser read the dots, and the an electrical signal, and output. However, the the marketplace until Philips by James T. Russell, dots of light and dark. data was converted to finally to audio or visual technology didn't appear in and Sony came out with the compact disc (CD) in 1982. Since then, there has been a constant succession of optical disc formats, first in CD formats, followed by a number of DVD formats. Optical disc offers a number of advantages over magnetic storage media. An optical disc holds much more data. The greater control and focus possible with laser beams (in comparison to tiny magnetic heads) means that more smaller space. Storage each new generation Emerging standards, data can be written into a capacity of increases optical with media. such as Blu-ray, offer up on In a single-sided 12- to 27 gigabytes (GB) centimeter disc. comparison, a diskette, for example, can hold 1.44 megabytes (MB). Optical discs are inexpensive to manufacture and data stored on them is relatively impervious to most environmental threats, such as power surges, or magnetic disturbances. CD-ROM CD-ROM (Compact Disc, read-only-memory) is an adaptation of the CD that is designed to store computer data in the form of text and graphics, as well as hi-fi stereo sound. The was defined by Philips and Book. Other standards with it to define original data format standard Sony in the 1983 Yellow are used in conjunction directory 9660, for and file HFS Macintosh structures, including ISO (Hierarchal File System, computers), and Hybrid HFS-ISO. Format of the CDs: a standard CD is 120 mm CD-ROM is the same as for audio (4.75 inches) in diameter and 1.2 mm (0.05 inches) thick and is composed of a polycarbonate plastic substrate (under layer – this is the main body of the disc), one or more thin reflective metal (usually aluminum) layers, and a lacquer coating. The Yellow Book specifications were so general that there was some fear in the industry that multiple incompatible and proprietary formats would be created. In order to prevent such an occurrence, representatives from industry leaders met at the High Sierra Hotel in Lake Tahoe to collaborate on a common standard. Nicknamed the High Sierra Format, this version was later modified to become ISO 9660. Today, CD-ROMs are standardized and will work in any standard CD-ROM drive. CD-ROM drives can also read audio compact discs for music, although CD players cannot read CD-ROM discs. CD-ROM Data Storage Although the disc media and the drives of the CD and CD-ROM are, in principle, the same, there is a difference in the way data storage is organized. Two new sectors were defined, Mode 1 for storing computer data and Mode 2 for compressed audio or video/graphic data. CD-ROM Mode 1 CD-ROM Mode 1 is the mode used for CD-ROMs that carry data and applications only. In order to access the thousands of data files that may be present on this type of CD, precise addressing is necessary. Data is laid out in nearly the same way as it is on audio disks: data is stored in sectors (the smallest separately addressable block of information), which each hold 2,352 bytes of data, with an additional number of bytes used for error detection and correction, as well as control structures. For mode 1 CD-ROM data storage, the sectors are further broken down, and 2,048 used for the expected data, while the other 304 bytes are devoted to extra error detection and correction code, because CD-ROMs are not as fault tolerant as audio CDs. There are 75 sectors per second on the disk, which yields a disc capacity of 681,984,000 bytes (650MB) and a single speed transfer rate of 150 kbps, with higher rates for faster CD-ROM drives. Drive speed is expressed as multiples of the single speed transfer rate, as 2X, 4X, 6X, and so on. Most drives support CD-ROM XA (Extended Architecture) and Photo-CD (including multiple session discs). CD-ROM Mode 2 CD-ROM Mode 2 is used for compressed audio/video information and uses only two layers of error detection and correction, the same as the CD-DA. Therefore, all 2,336 bytes of data behind the sync and header bytes are for user data. Although the sectors of CD-DA, CD-ROM Mode 1 and Mode 2 are the same size, the amount of data that can be stored varies considerably because of the use of sync and header bytes, error correction and detection. The Mode 2 format offers a flexible method for storing graphics and video. It allows different kinds of data to be mixed together, and became the basis for CDROM XA. Mode 2 can be read by normal CD-ROM drives, in conjunction with the appropriate drivers. Data Encoding and Reading The CD-ROM, like other CD adaptations, has data encoded in a spiral track beginning at the center and ending at the outermost edge of the disc. The spiral track holds approximately 650 MB of data. That's about 5.5 billion bits. The distance between two rows of pits, measured from the center of one track to the center of the next track is referred to as track pitch. The track pitch can range from 1.5 to 1.7 microns, but in most cases is 1.6 microns. Constant Linear Velocity (CLV) is the principle by which data is read from a CDROM. This principal states that the read head must interact with the data track at a constant rate, whether it is accessing data from the inner or outermost portions of the disc. This is affected by varying the rotation speed of the disc, from 500 rpm at the center, to 200 rpm at the outside. In a music CD, data is read sequentially, so rotation speed is not an issue. The CD-ROM, on the other hand, must read in random patterns, which necessitates constantly shifting rotation speeds. Pauses in the read function are audible, and some of the faster drives can be quite noisy because of it. Magnetic Tape The use of magnetic media to record and store numeric and textual information, sound, motion, and still images has presented librarians and archivists with opportunities and challenges. On the one hand, magnetic media increase the kinds of artifacts and events we can capture and store. On the other hand, their special long-term storage needs are different from traditional library materials, confusing to those in charge of their care, and demanding of resources not always available to libraries and archives. Audio and video collections require specific care and handling to ensure that the recorded information will be preserved. Special storage environments may be required if the recorded information is to be preserved for longer than ten years. For information that must be preserved indefinitely, periodic transcription from old media to new media will be necessary, not only because the media are unstable, but because the recording technology will become obsolete. As an information storage medium, magnetic tape is not as stable as film or paper. Properly cared for, film and nonacid paper can last for centuries, whereas magnetic tape will only last a few decades. Use of magnetic media for storage is further confounded by the prevalence of several formats (e.g., U-mastic, VHS, S-VHS, 8mm, and Beta Cam for video), media types (iron oxide, chromium dioxide, barium ferrite, metal particulate, and metal evaporated), and by rapid advances in media technology. On the other hand, books have virtually maintained the same format for centuries, have almost exclusively used ink on paper as the information storage medium, and require no special technology to access the recorded information. Likewise, newer microfilm, microfiche, and movie film are known for their stability when kept in proper environments, and viewing formats have not changed significantly over the years. (The breakdown of acetate backing that plagues older film materials is discussed in Section 2.3: Substrate Deformation.) This report will compare care and handling procedures for tapes with procedures for paper and film whenever possible. Zip Drives A Zip drive is a small, portable disk drive used primarily for backing up and archiving personal computer files. The trademarked Zip drive was developed and is sold by Iomega Corporation. Zip drives and disks come in two sizes. The 100 megabyte size actually holds 100,431,872 bytes of data or the equivalent of 70 floppy diskettes. There is also a 250 megabyte drive and disk. The Iomega Zip drive comes with a software utility that lets you copy the entire contents of your hard drive to one or more Zip disks. In addition to data backup, Iomega suggests these additional uses: • Archiving old e-mail or other files you don't use any more but may want to access someday • Storing unusually large files, such as graphic images that you need infrequently • Exchanging large files with someone • Putting your system on another computer, perhaps a portable computer • Keeping certain files separate from files on your hard disk (for example, personal finance files) The Zip drive can be purchased in either a parallel or a Small Computer System Interface (SCSI) version. In the parallel version, a printer can be chained off the Zip drive so that both can be plugged into your computer's parallel port. DVD DVD (digital versatile disc) is an optical disc technology that is expected to rapidly replace the CD-ROM disc (as well as the audio compact disc) over the next few years. The digital versatile disc (DVD) holds 4.7 gigabyte of information on one of its two sides, or enough for a 133-minute movie. With two layers on each of its two sides, it will hold up to 17 gigabytes of video, audio, or other information. (Compare this to the current CD-ROM disc of the same physical size, holding 600 megabyte. The DVD can hold more than 28 times as much information!) DVD-Video is the usual name for the DVD format designed for full-length movies and is a box that will work with your television set. DVD-ROM is the name of the player that will (sooner or later) replace your computer's CD-ROM. It will play regular CDROM discs as well as DVDROM discs. DVD-RAM is the writeable version. DVD Audio is a player designed to replace your compact disc player. DVD uses the MPEG-2 file and compression standard. MPEG-2 images have four times the resolution of MPEG-1 images and can be delivered at 60 interlaced fields per second where two fields constitute one image frame. (MPEG-1 can deliver 30 nonintegrated frames per second.) Audio quality on DVD is comparable to that of current audio compact discs. NETWORKS NETWORKS Introduction After learning the section you will be able to describe Communication, Data Communications, Data Transmission, Networks, and different Hardware and software used to communicate between computers effectively. Computer Network and Usage A network is a collection of computers and devices connected by communications channels that facilitates communications among users and allows users to share resources with other users. Some examples of resources are data, information, hard ware, and software. The following paragraphs explain the advantages of using a network. Facilitating Communications Using a network, people can communicate efficiently and easily via email, instant messaging, chat rooms, telephony, video telephone calls, and videoconferencing. Sometimes these communications occur within a business’s network. Other times, they occur globally through the Internet. As discussed earlier in this chapter, users have a multitude of devices available to send and receive communications. Sharing Hardware In a networked environment, each computer on a network can access and use hardware on the network. Suppose several personal computers on a network each require the use of a laser printer. If the personal computers and a laser printer are connected to a network, the personal computer users each can access the laser printer on the network, as they need it. Business and home users network their hardware for one main reason. That is, it may be too costly to provide each user with the same piece of hardware such as a printer. Sharing Data and Information In a networked environment, any authorized computer user can access data and information stored on other computers on the network. A large company, for example, might have a database of customer information. Any authorized per son, including a mobile user using a handheld computer to connect to the network, can access this database. The capability of providing access to and storage of data and information on shared storage devices is an important feature of many networks. Sharing Software Users connected to a network can access software (programs) on the network. To support multiple user access of software, most software vendors sell network versions of their software. In this case, software vendors issue a site license. A site license is a legal agreement that allows multiple users to run the software package simultaneously. The site license fee usually is based on the number of users or the number of computers attached to the network. Sharing software via a network usually costs less than buying individual copies of the software package for each computer. Many mobile users today access their company networks through a virtual private network. When a mobile user connects to a main office using the Internet, a virtual private network (VPN) provides the mobile user with a secure connection to the company network server, as if the user had a private line. VPNs help to ensure that transmitted data is safe from being intercepted by unauthorized people. Problems Associated with Standalone Computers Sharing Hardware devices such as printers, scanners and Hard Disks. Difficulties in sharing software. Difficulties in sharing data and Information. Storage problems. Difficulties of communication between computers. Introduction Computers were stand-alone devices when first introduced. As they became more widely used, manufacturers designed hardware and software so one computer could communicate with another. Computer communications describes a process in which one computer transfers data, instructions, and information to another computer(s). Originally, only large computers had communications capabilities. Today, even the smallest computers and devices can communicate with one another. The Internet provides a means for worldwide communications. What is a Communication? The following picture shows a sample communications system. As illustrated in this figure, communications systems contain all types of devices. An example of a communications system. Some devices that can serve as sending and receiving devices are a) Personal computers b) Notebook computers c) Web enabled cellular telephones d) Web-enabled handheld computers e) MSN TV f) GPS receivers The communications channel consists of telephone lines, underground cables, microwave stations, and satellites. The primary function of a communications device, such as a modem, is to convert or format signals so they are suitable for the communications channel or a receiving device. When using a telephone line as the communications channel, you need a modem to convert between analog and digital signals. An analog signal consists of a continuous electrical wave. Computers, however, process data as digital signals. A digital signal consists of individual electrical pulses that represent the bits grouped together into bytes. For instance, a modem connected to a sending computer converts the computer’s digital signals into analog signals. The analog signals then travel over a communications channel, such as a standard telephone line. At the receiving end, another modem converts the analog signals back into digital signals that a receiving computer can recognize. Sending and Receiving Devices Sending and receiving devices initiate or accept transmission of data, instructions, and information. Notebook computers, desktop computers, midrange servers, and main frame computers all can serve as sending and receiving devices. These computers can communicate directly with another computer, with hundreds of computers on a company network, or with millions of other computers on the Internet. A modem converts the individual electrical pulses of a digital signal into analog signals for data transmission over some telephone lines. At the receiving computer, another modem converts the analog signals back into digital signals that the computer can process. Basic Requirements for Successful Communications For successful communications, you need the following: A sending device that initiates an instruction to transmit data, instructions, or information. A communications device that converts or formats the data, instructions, or information from the sending device into signals carried by a communications channel. A communications channel, or path, on which the signals travel. A communications device that receives the signals from the communications channel and converts or formats them so the receiving device can recognize the signals. A receiving device that accepts the transmission of data, instructions, or information. Communication Types Simplex Communication Simplex data communication specifies that communication on a given channel can only flow in one direction. In this environment, only one entity is allowed to transmit and all others act as receivers. It should be noted that the sending device cannot receive data and the receiving entity cannot transmit data. Perhaps a good analogy of this type of communication would be your local radio station. The radio station broadcasts a message (the transmitting device) and you receive the message on your radio (the receiving device). This represents a one-way communication stream. Simplex Communication Data transfer in one direction only. Half-Duplex Communication Unlike simplex communication, half-duplex communication allows each device to send and receive data, but only one device at a time can transmit. A key point is that when you are transmitting the entire channel is being used for that purpose. You cannot receive and transmit at the same time. The best example of this would be a child’s walkie-talkie. You push a button to talk and release it to receive. It can best be stated by saying half- duplex provides for bidirectional communication, but only in one direction at a time. Half-Duplex Communication Data transfer both directions but only one direction at a time. Full-Duplex Communication Full-duplex communication provides for two-way communicate at the same time. An everyday example of full-duplex communication would be your basic telephone system. Unlike the walkie-talkies (half duplex), full-duplex communication allows both parties to transmit and receive at the same time. Full-Duplex Communication Data transfer both directions at the same time. Data Communication Analog Signal In telecommunications, an analog signal is one in which a base carrier's alternating current frequency is modified in some way, such as by amplifying the strength of the signal or varying the frequency, in order to add information to the signal. Broadcast and telephone transmission have conventionally used analog technology. An analog signal can be represented as a series of sine waves. The term originated because the modulation of the carrier wave is analogous to the fluctuations of the human voice or other sound that is being transmitted. Analog describes any fluctuating, evolving, or continually changing process. Digital Signal Digital describes electronic technology that generates, stores, and processes data in terms of two states: positive and non-positive. Positive is expressed or represented by the number 1 and non-positive by the number 0. Thus, data transmitted or stored with digital technology is expressed as a string of 0's and 1's. Each of these state digits is referred to as a bit (and a string of bits that a computer can address individually as a group is a byte). Prior to digital technology, electronic transmission was limited to analog technology, which conveys data as electronic signals of varying frequency or amplitude that are added to carrier waves of a given frequency. Broadcast and phone transmission has conventionally used analog technology. Digital technology is primarily used with new physical communications media, such as satellite and fiber optic transmission. A modem is used to convert the digital information in your computer to analog signals for your phone line and to convert analog phone signals to digital information for your computer. Types of Transmission Media Transmission Media, Network Cables and Connectors Perhaps the most important network components are the media and connectors used to attach computers to the system. The word “media” simply refers to the physical pathway on which network data travels. In most cases, this media is some type of cable. We refer to these cables as bounded media. Within the networking environment, many different types of bounded media are used. Each of these has very different characteristics such as speed, maximum length and connection types. The following is a list of the most common type of cables: Cable media Coaxial cable, Unshielded twisted pair cable, Shielded twisted pair cable, Fiber optic cable. Wireless media Radio Frequency, Infrared, Microwave. Twisted Pair Twisted pair cable consists of at least two insulated wires twisted together to reduce the effects of crosstalk. There are two broad categories of twisted pair cables. They are UTP (unshielded twisted pair cable) and STP (shielded twisted pair cable). STP (Shielded Twisted Pair) cable is very resistant to environmental factors like EMI because of the added layer of shielding that surrounds the twisted wires. STP cable tends to be more expensive than UTP and is also harder to work with than the thinner unshielded variety. The most common implementation of STP is for IBM Token ring cables. UTP (Shielded Twisted Pair), as the name would imply, does not have an added layer of shielding and is therefore thinner and cheaper to manufacture. UTP cable is rated in categories: Category 3 and 5 are the most common for data grade transmissions. The CAT 3 cable was dominant in the early years of networking but has been replaced by CAT 5 wiring because. CAT 5 is better able to create a stable platform for data transmissions greater than 10 Mbps. The CAT 5 twisted pair cable can support speeds of 100 Mbps. The main physical difference between CAT 3 and CAT 5 cable is the number of twists per inch. The CAT 5 cable has many more twists than CAT 3, eliminating most crosstalk. UTP cable closely resembles the cable used by telephones in your home. Coaxial Cable Coaxial cable, typically called coax cable, uses a center core conductor that is insulated and surrounded by either a braided or solid thin foil aluminum shield. Coax cable is very similar in appearance to the type used by television cable companies in your home. However, it should be noted that these are not the same and can not be interchanged. Due to the amount of shielding, coax cable is very resistant to crosstalk (interference from adjacent wires) and EMI (electromagnetic interference). The graphic below shows that a coax cable is composed of an outer jacket, an outer shield, an insulator and the center conductor. Fiber Optic Fiber optic cable uses a small strand of glass or plastic, instead of copper, as the core of the cable. It consists of a glass center core surrounded by a plastic sheath and a layer of gel or wire stands. Fiber optic cable offers a major advantage over copper wire. It is almost completely immune to EMI and does not suffer from attenuation (loss of signal strength over distance) like copper cable. Fiber cable tends to be very expensive as compared to copper wire. However, this cost variance should decrease as more companies choose to implement this technology. Advantages over copper-based media: Supports greater distances (up to 4 kilometers) Immune to EMI (Electromagnetic Interference) Immune to RFI (Radio Frequency Interference) Disadvantages of Fiber-Optic Cable: More expensive than copper-based media Difficult to install and support. Wireless Media After discussing coaxial, twisted pair and fiber optic cable, one might get the impression that these are the only media options available. Copper and fiber optic cabling are by far the most prevalent implementations. However, there is another option that is gaining more acceptances in the networking world. This option is wireless media. Wireless technology is not new. In fact, the technology has been around for many years. This technology allows computers fitted with special wireless adapters (NICs) to communicate with other network devices, computers, printers, etc. without the use of cables. To date, wireless networks have been limited mostly to smaller workgroup environments supporting only a limited number of computers and peripheral devices. These wireless networks can also become part of a larger cabled network using special wireless ports called access points. The access point is actually a device that converts the wireless signal to a signal that can be placed on a cabled network. These devices can be dedicated access points or simply a computer equipped with both a wireless adapter and a conventional NIC, which is connected to the larger network via copper or fiber optic cable. There are basically two different types of technology used in wireless communications, RF (Radio Frequencies) and infrared technology. Of the two, infrared technology is the one most often implemented in workgroup environments. Whether using RF or infrared technologies, environmental conditions and distance factors will have a significant influence on the performance expectations of the network. The typical wireless access point can normally support up to about twenty computers within a 30 to 60 meter radius. This is would be under ideal conditions. Other factors, such as intervening walls and environmental conditions, may reduce performance and distance even further. Radio frequency Radio frequency (abbreviated RF, rf, or r.f.) is a term that refers to alternating current (AC) having characteristics such that, if the current is input to an antenna, an electromagnetic (EM) field is generated suitable for wireless broadcasting and/or communications. These frequencies cover a significant portion of the electromagnetic radiation spectrum, extending from nine kilohertz (9 kHz), the lowest allocated wireless communications frequency (it's within the range of human hearing), to thousands of gigahertz (GHz). Transmission of Digital Data A modem modulates outgoing digital signals from a computer or other digital device to analog signals for a conventional copper twisted pair telephone line and demodulates the incoming analog signal and converts it to a digital signal for the digital device. In recent years, the 2400 bits per second modem that could carry e-mail has become obsolete. 14.4 Kbps and 28.8 Kbps modems were temporary landing places on the way to the much higher bandwidth devices and carriers of tomorrow. From early 1998, most new personal computers came with 56 Kbps modems. By comparison, using a digital Integrated Services Digital Network adapter instead of a conventional modem, the same telephone wire can now carry up to 128 Kbps. With Digital Subscriber Line (DSL) systems, now being deployed in a number of communities, bandwidth on twisted-pair can be in the megabit range. Information Networks LAN A local area network (LAN) is a group of computers and associated devices that share a common communications line or wireless link and typically share the resources of a single processor or server within a small geographic area (for example, within an office building). Usually, the server has applications and data storage that are shared in common by multiple computer users. A local area network may serve as few as two or three users (for example, in a home network) or as many as thousands of users (for example, in an FDDI network). MAN A metropolitan area network (MAN) is a network that interconnects users with computer resources in a geographic area or region larger than that covered by even a large local area network (LAN) but smaller than the area covered by a wide area network (WAN). The term is applied to the interconnection of networks in a city into a single larger network (which may then also offer efficient connection to a wide area network). It is also used to mean the interconnection of several local area networks by bridging them with backbone lines. The latter usage is also sometimes referred to as a campus network. Examples of metropolitan area networks of various sizes can be found in the metropolitan areas of London, England; Lodz, Poland; and Geneva, Switzerland. Large universities also sometimes use the term to describe their networks. A recent trend is the installation of wireless MANs. WAN A wide area network (WAN) is a geographically dispersed telecommunications network. The term distinguishes a broader telecommunication structure from a local area network. A wide area network may be privately owned or rented, but the term usually connotes the inclusion of public (shared user) networks. An intermediate form of network in terms of geography is a metropolitan area network (MAN). Network Topology Network topology refers to how your network is wired (the physical configuration). Choosing the right configuration (topology) for a given situation can directly affect a network’s speed, its flexibility to expand and just how robust or fault- tolerant it is. There are many choices for designing a network topology. The most common choices are: 1. Bus 2. Star 3. Ring 4. Mesh 5. Hybrid It should be noted that there are many variations and hybrids of the above topologies. These topologies can exist separately or in a mixed environment. It should be stressed that a mixture of topologies is much harder to administrate and more difficult to troubleshoot. Bus The basic bus topology is relatively easy to install and requires the least amount of media (cable) as compared to the other topologies. Every computer or device is connected to the next in a daisy-chain fashion. The first and last device on the chain must be terminated with a resistor that matches the impedance of cable that you are using. While the bus topology is fairly easy to install, it can be one of the most difficult to troubleshoot. Another major limitation of a bus topology is that a cable fault or break anywhere down the length of the cable will affect all computers on that segment. The graphic below depicts an example of a bus topology. One very common implementation of the bus topology is Apple’s Local Talk, which is a proprietary Data Link layer implementation developed by Apple Computer for its AppleTalk protocol suite. Local Talk was designed as a cost-effective network solution for connecting local workgroups. Local Talk hardware typically is built into Apple products, which are easily connected by using inexpensive twisted-pair cabling. Local Talk networks are almost always organized in a bus topology. A Diagram of a Bus Topology Star The most important distinction between the bus topology and the star topology is that a star topology offers a much higher degree of redundancy. Unlike the bus topology where one fault could bring Dow n the entire network, the star connects each computer with its own dedicated cable. A failure of one cable will affect only that machine. A star topology also tends to be much more flexible if you have to move or reconfigure computers. The cost of this topology is somewhat higher with the added expense of using a hub or concentrator. However this cost is more than justified if you ever have the need to troubleshoot the cable plant. The example below depicts a star topology. A Diagram of a Star Topology Ring A ring topology is made up of computers that are connected in a circular configuration. Each computer or device in the ring is connected to two others. Data in this configuration travels around the ring in one direction and each device in the ring can also act as repeater to boost the signal if necessary. A ring topology generally uses more cable than either the bus or the star. A ring topology is shown below. A Diagram of a Ring Topology Hybrid A combination of any two or more network topologies. Note 1: Instances can occur where two basic network topologies, when connected together, can still retain the basic network character, and therefore not be a hybrid network. For example, a tree network connected to a tree network is still a tree network. Therefore, a hybrid network accrues only when two basic networks are connected and the resulting network topology fails to meet one of the basic topology definitions. For example, two star networks connected together exhibit hybrid network topologies. Note 2: A hybrid topology always accrues when two different basic network topologies are connected. A Diagram of a Hybrid Topology Mesh The mesh topology is by far the most redundant of all of the topologies mention so far. However, this does come with an added expense. The mesh topology requires much more cable than any of the other topologies. In a true mesh topology, every device is directly connected to every other device. It is this configuration that makes it so redundant. However, if there ever is a problem, it can be very difficult to locate the offending cable. The example below depicts a mesh topology. A Diagram of a Mesh Topology Network Operating Systems A Network Operating System (NOS) is a specific kind of program designed to allow users to share resources over a computer network. These resources may include other programs and files as well as printers and other hardware. The Network Operating System sets the rules for this sharing of resources and allows a variety of kinds of computers and components to communicate. The most significant Network Operating Systems today are Microsoft’s Windows NT and Windows 2000, Novell NetWare and the different versions of UNIX and Linux. Client/Server Networking One concept that is important in our discussion of Operating Systems is the concept of client/server networking. In this section, we will focus on the server side of networking. In an o future section we will turn our focus to the client side. Servers In a client/server networking environment, certain systems are set up as servers, which means that they serve resources to other systems. Servers can provide various functions. For example, a server might be set up as a print server in order to manage the printing on a network. Or a server might play the role of a file server, hosting files on a network so that users can share and access files were the network. Servers may also act as application servers to host applications that are used on the network. Another important role that is frequently performed by servers is to control security on the network to ensure that only authorized users are able to access network resources. It is important to note that typically servers are the bigger, faster machines on the network and are often dedicated servers that perform very specific functions. There are instances, however, when a server may act as both a server and a client. Clients Very simply, clients are the systems on the network that request and access information from the servers. These are the systems that end users sit at to perform their work. Another term that is used almost interchangeably with client is workstation. OSI Model In response to the need for networking standards, various industry organizations attempted to create models. Most of these models dealt with the issues of moving information or data from one location to another. The work of these various industry organizations laid the groundwork for what was to become the most widely accepted model for networking, the OSI (Open Systems Interconnection) model. In about 1977, the ISO (International Organization for Standards) adopted a mandate to develop a set of standards that would address the issues of interoperability in a multivendor environment. The fruits of their labor became the OSI model. The OSI model subdivides the intricacies of networking into seven separate parts: 1. Application 2. Presentation 3. Session 4. Transport 5. Network 6. Data link 7. Physical It is important to keep in mind that the OSI model is a design or blueprint for how communication should occur. It attempts to divide the otherwise complicated task of communication between devices into logical sub groups called layers. This process is somewhat akin to the task of building a house. Viewing this process as a whole can be quite overwhelming. However, most houses are built by subcontractors, each specializing in a particular area. This is exactly what the OSI model does for networking, creating individual layers at which software and hardware vendors can function. This means, for example, that a manufacturer of network interface cards needs only to be familiar with standards set by the lower layers of the OSI model, while a software vendor of a terminal emulation program might be concerned only with the upper few layers of the model. What is a Protocol? When data is being transmitted between two or more devices something needs to govern the controls that keep this data intact. A formal description of message formats and the rules two computers must follow to exchange those messages. Protocols can describe low-level details of machine-to-machine interfaces (e.g., the order in which hits and bytes are sent across wire) or highlevel exchanges between application programs (e.g., the way in which two programs transfer a file across the Internet) TCP/IP TCP The main function of TCP is to establish and monitor connections between the sending and receiving devices. TCP is responsible for providing reliable connection-oriented data delivery. TCP functions at the Transport layer of the OSI model. When you are using TCP, you basically have an acknowledgement between sender and receiver that is maintained the entire length of the data transmission. IP Internet Protocol provides the mechanism for Internet addressing. IP functions at the Network layer of the OSI model. There are basically two parts to an IP address; the first part defines the network a device is attached to, and the second portion identifies the actual device itself. An IP address can be assigned by the network administrator or assigned by a DHCP (Dynamic Host Configuration Protocol) server. NetBEUI NetBEUI (NetBIOS Extended User Interface) is a new, extended version of NetBIOS, the program that lets computers communicates within a local area network. NetBEUI (pronounced net-BOO-ee) formalizes the frame format (or arrangement of information in a data transmission) that was not specified as part of NetBIOS. NetBEUI was developed by IBM for its LAN Manager product and has been adopted by Microsoft for its Windows NT, LAN Manager, and Windows for Workgroups products. Hewlett-Packard and DEC use it in comparable products. NetBEUI is the best performance choice for communication within a single LAN. Because, like NetBIOS, it does not support the routing of messages to other networks, its interface must be adapted to other protocols such as Internet work Packet Exchange or TCP/IP. A recommended method is to install both NetBEUI and TCP/IP in each computer and set the server up to use NetBEUI for communication within the LAN and TCP/IP for communication beyond the LAN. IPX/SPX IPX (Internet work Packet Exchange) is a networking protocol from Novell that interconnects networks that use Novell's NetWare clients and servers. IPX is a datagram or packet protocol. IPX works at the Network layer of communication protocols and is connectionless (that is, it doesn't require that a connection be maintained during an exchange of packets as, for example, a regular voice phone call does). Packet acknowledgment is managed by another Novell protocol, the Sequenced Packet Exchange (SPX). Other related Novell NetWare protocols are: the Routing Information Protocol (RIP), the Service Advertising Protocol (SAP), and the NetWare Link Services Protocol (NLSP). CHARACTERISTICS OF AN IPX/SPX NUMBER A datagram passed in an IPX internet work contains the following information: 1. A 30-byte IPX header (includes network, node, and socket number of both source and destination addresses) 2. Data section: includes SPX header (or some other type, but often SPX) Since IPX is connectionless, the minimum packet size is only 30-bytes (excluding MAC header). Since SPX provides reliable connections (but is not mandatory) it may not be included. IPX has a maximum packet size of 65,535 bytes (includes data obviously). The MAC header comes before the IPX header and the data. Now, the IPX network number is 4-bytes, hexadecimal. This is the basis for packet routing. Each destination in internet work has their own number. The network number may contain up to eight digits, wile leading zeroes are often not displayed. Novell Server can automatically detect network numbers on the internet work. Routers send a RIP request packet to determine network numbers and frame types to use. The Node number is 6 bytes, hexadecimal. This number uniquely identifies a device on the internet work and is akin to the interface connected to that device. This number need only be unique in the IPX network to which it is a member. HTTP HTTP (Hypertext Transfer Protocol) is in widespread use today. HTTP is used to transfer Web pages from a Web server to a local Web browser. Those Web pages are created as HTML (Hypertext Markup Language) documents. HTTP also has a sister protocol called HTTP(S), which allows for secure transfer of documents. While HTTPS is slower due to the overhead generated by encryption methods, most would agree that it is essential for e-commerce and on-line banking transactions. FTP FTP (File Transfer Protocol) is somewhat unique in that it is both a protocol and a program. It is usually associated most closely with the UNIX environment. As the name would indicate, it is used to transfer files. It is very powerful and flexible in its use. It can be configured to let users take files but not transmit them. This could be very advantageous in the case of limiting the transfer of files that may contain a virus. There is also a stripped down version of FTP called TFTP (Trivial File Transfer Protocol) which lacks some of the functionality of FTP in particular the ability to browse for files. Most FTP access is granted using the “anonymous” user account. FTP can be very useful when troubleshooting or servicing an IP-based network. It can be used to download fixes, patches and standard ASCII read me files. The FTP utility is actually a collection of separate FTP commands. The list below displays some of the most popular commands along with their use. Help Displays Help screen for commands CD Changes the directory on a remote disk LCD Changes the directory on a local disk DIR Displays a descriptive list of files on remote computers BINARY Transfers a binary file format ASCII Transfers an ASCII file format PUT Transmits files to remote computers GET Retrieves files from remote computers QUIT/BYE Ends and exits an FTP session SMTP SMTP (Simple Mail Transfer Protocol) provides a mechanism to send email between dissimilar operating systems. It is SMTP’s ability to send email between different operating systems that makes it so useful on the Internet. An example of this would be composing an email message from a Windows 98 client, forwarding that to a local Microsoft Exchange Server which could then send it via the Internet to a server running the UNIX operating system. NNTP NNTP (Network News Transfer Protocol) is the predominant protocol used by computer clients and servers for managing the notes posted on Usenet newsgroups. NNTP replaced the original Usenet protocol, UNIX-to-UNIX Copy Protocol (UUCP) some time ago. NNTP servers manage the global network of collected Usenet newsgroups and include the server at your Internet access provider. An NNTP client is included as part of a Netscape, Internet Explorer, Opera, or other Web browser or you may use a separate client program called a newsreader. P0P3 The POP3 (Post Office Protocol) version 3 is used to download email from various servers to an email client. Microsoft’s Outlook Express is an example of client-side software that uses POP3 technology. Most ISPs (Internet Service Providers) that provide home service also use the POP3 protocol. This enables the ISP to download messages to the individual user’s computer rather than having to store them on the ISP’s servers. Network Components Network Interface Card The NIC is perhaps the most common component in the network. At least one NIC must be installed in every system attached to the network. The NIC is an expansion board that allows the workstation or server to attach to a common cabling system. Most network interface cards provide for more than just one cable type. The most common connection types are twisted pair (RJ45), coax (BNC) connectors and fiber optic connections. Cables and Connectors Coaxial Cable Coaxial cable is the kind of copper cable used by cable TV companies between the community antenna and user homes and businesses. Coaxial cable is sometimes used by telephone companies from their central office to the telephone poles near users. It is also widely installed for use in business and corporation Ethernet and other types of local area network. Coaxial cable is called “coaxial” because it includes one physical channel that carries the signal surrounded (after a layer of insulation) by another concentric physical channel, both running along the same axis. The outer channel serves as a ground. Many of these cables or pairs of coaxial tubes can be placed in a single outer sheathing and, with repeaters, can carry information for a great distance. Coaxial cable was invented in 1929 and first used commercially in 1941. AT&T established its first cross-continental coaxial transmission system in 1940. Depending on the carrier technology used and other factors, twisted pair copper wire and optical fiber are alternatives to coaxial cable. BNC Connector used with Coaxial Cable A BNC (Bayonet Neil-Concelman, or sometimes British Naval Connector) connector is used to connect a computer to a coaxial cable in a 10BASE-2 Ethernet network. 10BASE-2 is a 10 MHz base band network on a cable extending up to 185 meters - the 2 is a rounding up to 200 meters - without a repeater cable. 10BASE-2 Ethernets are also known as “Thin net”, “thin Ethernet”, or “cheaper nets”. The wiring in this type of Ethernet is thin, 50 ohm, base band coaxial cable. The BNC connector in particular is generally easier to install and less expensive than other coaxial connectors. A BNC male connector has a pin that connects to the primary conducting wire and then is locked in place with an outer ring that turns into locked position. Different sources offer different meanings for the letters BNC. However, our most knowledgeable source indicates that the B stands for a bayonet-type connection (as in the way a bayonet attaches to a rifle) and the NC for the inventors of the connector, Neil and Concelman. Twisted Pair Twisted pair is the ordinary copper wire that connects home and many business computers to the telephone company. To reduce crosstalk or electromagnetic induction between pairs of wires, two insulated copper wires are twisted around each other. Each connection on twisted pair requires both wires. Since some telephone sets or desktop locations require multiple connections, twisted pair is sometimes installed in two or more pairs, all within a single cable. For some business locations, twisted pair is enclosed in a shield that functions as a ground. This is known as shielded twisted pair (STP). Ordinary wire to the home is unshielded twisted pair (UTP). Twisted pair is now frequently installed with two pairs to the home, with the extra pair making it possible for you to add another line (perhaps for modem use) when you need it. Twisted pair comes with each pair uniquely color coded when it is packaged in multiple pairs. Different uses such as analog, digital, and Ethernet require different pair multiples. Although twisted pair is often associated with home use, a higher grade of twisted pair is often used for horizontal wiring in LAN installations because it is less expensive than coaxial cable. The wire you buy at a local hardware store for extensions from your phone or computer modem to a wall jack is not twisted pair. It is a side-by-side wire known as silver satin. The wall jack can have as many five kinds of hole arrangements or pin outs, depending on the kinds of wire the installation expects will be plugged in (for example, digital, analog, or LAN) . (That’s why you may sometimes find when you carry your notebook RJ45 Connectors are used with Twisted pair cables. In the U. S., telephone jacks are also known as registered jacks, sometimes described as RJ-XX, and are a series of telephone connection interfaces (receptacle and plug) that are registered with the U.S. Federal Communications Commission (FCC). They derive from interfaces that were part of AT&T’s Universal Service Order Codes (USOC) and were adopted as part of FCC regulations (specifically Part 68, Subpart F. Section 68.502). The term jack sometimes means both receptacle and plug and sometimes just the receptacle. RJ-45 The RJ-45 is a single-line jack for digital transmission over ordinary phone wire, either untwisted or twisted. The interface has eight pins or positions. For connecting a modem, printer, or a data PBX at a data rate up to 19.2 Kbps, you can use untwisted wire. For faster transmissions in which you’re connecting to an Ethernet 10BASET network, you need to use twisted pair wire. (Untwisted is usually a flat wire like common household phone extension wire. Twisted is often round.) There are two varieties of RJ-45: keyed and unkeyed. Keyed has a small bump on its end and the female complements it. Both jack and plug must match. Fiber Optic Cable Fiber optic (or “optical fiber”) refers to the medium and the technology associated with the transmission of information as light impulses along a glass or plastic wire or fiber. Fiber optic wire carries much more information than conventional copper wire and is far less subject to electromagnetic interference. Most telephone company long-distance lines are now fiber optic. Transmission on fiber optic wire requires repeating at distance intervals. The glass fiber requires more protection within an outer cable than copper. For these reasons and because the installation of any new wiring is labor-intensive, few communities yet have fiber optic wires or cables from the phone company’s branch office to local customers (known as local loop). A Fiber Optic Cable Different kinds of Fiber Optic Connectors Hubs and Switches Hub In general, a hub is the central part of a wheel where the spokes come together. The term is familiar to frequent fliers who travel through airport “hubs” to make connecting flights from one point to another. In data communications, a hub is a place of convergence where data arrives from one or more directions and is forwarded out in one or more other directions. A hub usually includes a switch of some kind. (And a product that is called a “switch” could usually be considered a hub as well.) The distinction seems to be that the hub is the place where data comes together and the switch is what determines how and where data is forwarded from the place where data comes together. Regarded in its switching aspects, a hub can also include a router. 1. In describing network topologies, a hub topology consists of a backbone (main circuit) to which a number of outgoing lines can be attached (“dropped”), each providing one or more connection port for device to attach to. For Internet users not connected to a local area network, this is the general topology used by your access provider. Other common network topologies are the bus network and the ring network. (Either of these could possibly feed into a hub network, using a bridge.) 2. As a network product, a hub may include a group of modem cards for dial-in users, a gateway card for connections to a local area network (for example, an Ethernet or a Token Ring), and a connection to a line. Switch In a telecommunications network, a switch is a device that channels incoming data from any of multiple input ports to the specific output port that will take the data toward its intended destination. In the traditional circuitswitched telephone network, one or more switches are used to set up a dedicated though temporary connection or circuit for an exchange between two or more parties. On an Ethernet local area network (LAN), a switch determines from the physical device (Media Access Control or MAC) address in each incoming message frame which output port to forward it to and out of. In a wide area packet-switched network such as the Internet, a switch determines from the IP address in each packet which output port to use for the next part of its trip to the intended destination. In the Open Systems Interconnection (OSI) communications model, a switch performs the layer 2 or Data-Link layer function. That is, it simply looks at each packet or data unit and determines from a physical address (the “MAC address”) which device a data unit is intended for and switches it out toward that device. However, in wide area networks such as the Internet, the destination address requires a look-up in a routing table by a device known as a router. Some newer switches also perform routing functions (layer 3 or the Network layer functions in OSI) and are sometimes called IP switches. On larger networks, the trip from one switch point to another in the network is called a hop. The time a switch takes to figure out where to forward a data unit is called its latency. The price paid for having the flexibility that switches provide in a network is this latency. Switches are found at the backbone and gateway levels of a network where one network connects with another and at the sub network level where data is being forwarded close to its destination or origin. The former are often known as core switches and the latter as desktop switches. In the simplest networks, a switch is not required for messages that are sent and received within the network. For example, a local area network may be organized in a Token Ring or bus arrangement in which each possible destination inspects each message and reads any message with its address. Repeaters A repeater is a signal amplification device. As an electronic signal travels down a wire it weakens in strength. In electronic jargon this is known as attenuation. It’s much like a marathon runner getting tired and weakening as the race progresses. Repeaters are place at predetermined points along the cable and act to boost and retransmit the signal. This is like giving a runner a power bar or drink at crucial points in a race. Bridges A bridge is a hardware device that segments a single network into two or more logical pieces for the purpose of isolating network traffic. The operative word here is a single network. A bridge does NOT create another new network, because the segments still appear as one single network. Like a drawbridge that allows or prohibits traffic from passing from one side of the bridge to the other, a network bridge performs the same function in a network environment. The bridge will either pass network traffic or deny network traffic based on the destination address. If the intended address for a piece of data is located on the “local” segment, the bridge will block the traffic from passing beyond it onto other segments. On the other hand, if the destination address is on another segment, the bridge will allow the traffic to pass through in order to reach its destination. Let’s look at a simple example of why a bridge is used in a network environment. Let’s say that, within a single network, there is a small group of computer users that constantly exchange information and access network resources. On this same network, there is a larger group of users that do not use the network as much. If this network were not segmented, the first group would actually impact the performance of the second group in a negative way. However, if a bridge were used to segment the two groups, the first group of more intense network users would be isolated. The bridge would identify the traffic that belonged to the users on this local segment, and would prohibit it from passing out onto the rest of the network. Only the traffic intended for a computer located on the other side of the bridge will be allowed to pass. All other network traffic would remain on the local segment. Routers The router is considered to be an intelligent networking device. It performs basically two functions. First, it provides the physical connection between two or more different networks. The second and major function is to route packets of network information between different networks, hence the name “router.” The router also has the intelligence built in to dynamically adapt to changes in the network configuration and to route traffic around downed links. By implementing a number of routers to connect several smaller networks together, a larger entity known as an inter network is created. When a computer located on one network wants to send data to a device located on a remote network, the data is passed to a router located on the local segment (the default gateway). Brouters The brouter is a hybrid device that, as its name would imply, combines the functionality of both a bridge and a router into one device. It will function as a router in most cases. However, if it cannot locate the necessary routing information, it will perform a simple bridging function, either passing or denying network traffic based on the MAC destination address. Gateways If a router is considered an intelligent networking device, the gateway would be considered the device with a PhD. The gateway basically provides all the functionality of a router and acts as a translator as well. The router is a protocol- independent device, meaning it doesn’t really care what language a computer speaks. It is just interested in getting the message from one machine to another. The gateway performs the routing function as well as translating between different computer languages (protocols). An example of this could be the connection between a Windows NT/2 000 network and an IBM mainframe environment. The word default gateway refers to a router on the network that sends all TCP/IP packets to remote networks. The key point here is any or all packets are sent which are not destined for the local network! Because of the translation and other overhead involved, the gateway is the least rapid (slowest) of the Internet work Connection Devices. Firewalls A firewall is a set of related programs, located at a network gateway server that protects the resources of a private network from users from other networks. (The term also implies the security policy that is used with the programs.) An enterprise with an intranet that allows its workers access to the wider Internet installs a firewall to prevent outsiders from accessing its own private data resources and for controlling what outside resources its own users have access to. INTERNET & WWW Basic Concepts of Internet The Internet The Internet is a computer network made up of thousands of networks worldwide. No one knows exactly how many computers are connected to the Internet. It is certain, however, that these number in the millions. No one is in charge of the Internet. There are organizations which develop technical aspects of this network and set standards for creating applications on it, but no governing body is in control. The Internet backbone, through which Internet traffic flows, is owned by private companies. All computers on the Internet communicate with one another using the Transmission Control Protocol/Internet Protocol suite, abbreviated to TCP/IP. Computers on the Internet use client/server architecture. This means that the remote server machine provides files and services to the user’s local client machine. Software can be installed on a client computer to take advantage of the latest access technology. An Internet user has access to a wide variety of services: electronic mail, file transfer, vast information resources, interest group membership, interactive collaboration, multimedia displays, real-time broadcasting, shopping opportunities, breaking news, and much more. The Internet consists primarily of a variety of access protocols. Many of these protocols feature programs that allow users to search for and retrieve material made available by the protocol. Brief history The Internet (which most people know today as the World Wide Web or WWW) began in the United States in the 1960’s as a military project. It linked computers and people together so that if one military base was destroyed, information could still reach its destination simply by taking an alternative route. This approach to linking or networking computers is still the basis of the Internet. Academic institutions adopted this technology to allow co-operative work between universities, and the internet grew from there, although when the Internet first started, people could only share text-based documents. In 1990, the World Wide Web was developed. This made the internet very popular, because the WWW allowed people to access information through a graphical (picture based) interface such as the well-known browser, Netscape. Components of the Internet World Wide Web (WWW) The World Wide Web (abbreviated as the Web or WWW) is a system of Internet servers that supports hypertext to access several Internet protocols on a single interface. Almost every protocol type available on the Internet is accessible on the Web. This includes email, FTP, Telnet, and Usenet News. In addition to these, the World Wide Web has its own protocol: Hypertext Transfer Protocol, or HTTP. These protocols will be explained later in this document. The World Wide Web provides a single interface for accessing all these protocols. This creates a convenient and user-friendly environment. It is no longer necessary to be conversant in these protocols within separate, commandlevel environments. The Web gathers together these protocols into a single system. Because of this feature, and because of the Web’s ability to work with multimedia and advanced programming languages, the Web is the fastestgrowing component of the Internet. The operation of the Web relies primarily on hypertext as its means of information retrieval. Hypertext is a document containing words that connect to other documents. These words are called links and are selectable by the user. A single hypertext document can contain links to many documents. In the context of the Web, words or graphics may serve as links to other documents, images, video, and sound. Links may or may not follow a logical path, as each connection is programmed by the creator of the source document. Overall, the Web contains a complex virtual web of connections among a vast number of documents, graphics, videos, and sounds. Producing hypertext for the Web is accomplished by creating documents with a language called Hypertext Markup Language, or HTML. With HTML, tags are placed within the text to accomplish document formatting, visual features such as font size, italics and bold, and the creation of hypertext links. Graphics and multimedia may also be incorporated into an HTML document. HTML is an evolving language, with new tags being added as each upgrade of the language is developed and released. The World Wide Web Consortium (W3C), led by Web founder Tim Berners -Lee, coordinates the efforts of standardizing HTML. The W3C now calls the language XHTML and considers it to be an application of the XML language standard. The World Wide Web consists of files, called pages or home pages, containing links to documents and resources throughout the Internet. E-mail Electronic mail, or e-mail, allows computer users locally and worldwide to exchange messages. Each user of e-mail has a mailbox address to which messages are sent. Messages sent through e-mail can arrive within a matter of seconds. A powerful aspect of e-mail is the option to send electronic files to a person’s email address. Non-ASCII files, known as binary files, may be attached to e- mail messages. These files are referred to as MIME attachments. MIME stands for Multimedia Internet Mail Extension, and was developed to help e-mail software handle a variety of file types. For example, a document created in Microsoft Word can be attached to an e-mail message and retrieved by the recipient with the appropriate e-mail program. Many email programs, including Eudora, Netscape Messenger, and Microsoft Outlook, offer the ability to read files written in HTML, which is itself a MIME type. Telnet Telnet is a program that allows you to log into computers on the Internet and use online databases, library catalogs, chat services, and more. There are no graphics in Telnet sessions, just text. To Telnet to a computer, you must know its address. This can consist of words (locis.loc.gov) or numbers (140.147.254.3). Some services require you to connect to a specific port on the remote computer. In this case, type the port number after the Internet address. Example: telnet nri.reston.va.us 185. Telnet is available on the World Wide Web. Probably the most common Web-based resources available through Telnet have been library catalogs, though most catalogs have since migrated to the Web. A link to a Telnet resource may look like any other link, but it will launch a Telnet session to make the connection. A Telnet program must be installed on your local computer and configured to your Web browser in order to work. With the increasing popularity of the Web, Telnet has become less frequently used as a means of access to information on the Internet. FTP FTP stands for File Transfer Protocol. This is both a program and the method used to transfer files between computers. Anonymous FTP is an option that allows users to transfer files from thousands of host computers on the Internet to their personal computer account. FTP sites contain books, articles, software, games, images, sounds, multimedia, course work, data sets, and more. If your computer is directly connected to the Internet via an Ethernet cable, you can use one of several PC software programs, such as WS_FTP for Windows, to conduct a file transfer. Mail Discussion Groups One of the benefits of the Internet is the opportunity it offers to people worldwide to communicate via e-mail. The Internet is home to a large community of individuals who carry out active discussions organized around topic-oriented forums distributed by email. These are administered by software programs. Probably the most common program is the listserv. A great variety of topics are covered by listserv, many of them academic in nature. When you subscribe to a listserv, messages from other subscribers are automatically sent to your electronic mailbox. You subscribe to a listserv by sending an e-mail message to a computer program called a list server. List servers are located on computer networks throughout the world. This program handles subscription information and distributes messages to and from subscribers. You must have an e-mail account to participate in a listserv discussion group. Visit Tile.net at http://tile.net/ to see an example of a site that offers a searchable collection of e-mail discussion groups. UseNet News Usenet News is a global electronic bulletin board system in which millions of computer users exchange information on a vast range of topics. The major difference between Usenet News and e-mail discussion groups is the fact that Usenet messages are stored on central computers, and users must connect to these computers to read or download the messages posted to these groups. This is distinct from e-mail distribution, in which messages arrive in the electronic mailboxes of each list member. Usenet itself is a set of machines that exchanges messages, or articles, from Usenet discussion forums, called newsgroups. Usenet administrators control their own sites, and decide which (if any) newsgroups to sponsor and which remote newsgroups to allow into the system. There are thousands of Usenet newsgroups in existence. While many are academic in nature, numerous newsgroups are organized around recreational topics. Much serious computerrelated work takes place in Usenet discussions. A small number of e-mail discussion groups also exist as Usenet newsgroups. The Usenet news feed can be read by a variety of newsreader software programs. For example, the Netscape suite comes with a newsreader program called Messenger. Newsreaders are also available as standalone products. Chat and Instant Massaging Chat programs allow users on the Internet to communicate with each other by typing in real time. They are sometimes included as a feature of a Web site, where users can log into the “chat room” to exchange comments and information about the topics addressed on the site. Chat may take other, more wide-ranging forms. For example, America Online is well known for sponsoring a number of topical chat rooms. Internet Relay Chat (IRC) is a service through which participants can communicate to each other on hundreds of channels. These channels are usually based on specific topics. While many topics are frivolous, substantive conversations are also taking place. To access IRC, you must use an IRC software program. A variation of chat is the phenomenon of instant messaging. With instant messaging, a user on the Web can contact another user currently logged in and type a conversation. Most famous is America Online’s Instant Messenger. ICQ, MSN and Yahoo are other commonly-used chat programs. Evolution of Internet The history of the Internet begins at the height of the cold war in the 1960’s. People at the Rand Corporation, America’s foremost military think tank, were trying to figure out an important strategic problem: how could US authorities talk to each other in the aftermath of a nuclear attack? Communication networks of the day were chained point-to-point, with each place on the network dependent on the link before it. If one point in the network was blown up, the whole network would become useless. Paul Baran, one of the Rand thinkers on the project, conceived the idea for a new kind of communications network; one that wasn’t organized point-to-point, but instead was set up more like a fishnet. He believed this structure could allow information to find its own path through the network even if a section had been destroyed. His eleven volume report for the Pentagon was eventually shelved; but younger engineers realized that he had hit on an essential idea. Baran’s Cold War musings later influenced the design used to create a small, decentralized network connecting computers at four university campuses around the United States. This tiny seed eventually grew into the Internet; a huge network-of networks, millions of nodes strong, which today covers the entire globe. The Internet has come a long way from its military beginnings. Touching almost every aspect of society, it is now more likely to be used to plan a family vacation than to transmit military secrets. Following are highlights of the 30 year history of the Internet; how it grew, what technologies grew with it, and the impact of success on the Internet itself. 1962 - 1969 The Internet is first conceived in the early ’60s. Under the leadership of the Department of Defense’s Advanced Research Project Agency (ARPA), it grows from a paper architecture into a small network (ARPANET) intended to promote the sharing of supercomputers amongst researchers in the United States. 1962 – The RAND Corporation begins research into robust, distributed communication networks for military command and control. 1965 - ARPA sponsors research into a “cooperative network of timesharing computers.” 1967 - Delegates at a symposium for the Association for Computing Machinery in Gatlinburg, TN discuss the first plans for the ARPANET. 1969 - Researchers at four US campuses create the first hosts of the ARPANET, connecting Stanford Research Institute, UCLA, UC Santa Barbara, and the University of Utah. 1970 - 1973 The ARPANET is a success from the very beginning. Although originally designed to allow scientists to share data and access remote computers, email quickly becomes the most popular application. The ARPANET becomes a high-speed digital post office as people use it to collaborate on research projects and discuss topics of various interests. 1971 - The ARPANET grows to 23 hosts connecting universities and government research centers around the country. 1972 - The Inter Networking Working Group becomes the first of several standards-setting entities to govern the growing network. Vinton Cerf is elected the first chairman of the INWG, and later becomes known as a “Father of the Internet.” 1973 - The ARPANET goes international with connections to University College in London, England and the Royal Radar Establishment in Norway. 1974 - 1981 The general public gets its first vague hint of how networked computers can be used in daily life as the commercial version of the ARPANET goes online. The ARPANET starts to move away from its military/research roots. · 1974 - Bolt, Beranek & Newman opens Telnet, the first commercial version of the ARPANET. 1976 - Queen Elizabeth goes online with the first royal email message. 1979 - Tom Truscott and Jim Ellis, two graduate students at Duke University, and Steve Bellovin at the University of North Carolina establish the first USENET newsgroups. Users from all over the world join these discussion groups to talk about the net, politics, religion and thousands of other subjects. 1981 - ARPANET has 213 hosts. A new host is added approximately once every 20days. 1982 - 1987 Bob Kahn and Vinton Cerf are key members of a team which creates TCP/IP (Transmission Control Protocol/Internet Protocol: TCP makes sure data arrives correctly and in the proper order. IP specifies the way in which data will be communicated between two computers on a network), the common language of all Internet computers. For the first time the loose collection of networks which made up the ARPANET is seen as an “Internet”, and the Internet as we know it today is born. The mid-80s marks a boom in the personal computer and super-minicomputer industries. The combination of inexpensive desktop machines and powerful, network-ready servers allows many companies to join the Internet for the first time. Corporations begin to use the Internet to communicate with each other and with their customers. 1982 - The term “Internet” is used for the first time. 1984 - William Gibson coins the term “cyberspace” in his novel “Necromancer.” The number of Internet hosts exceeds 1,000. 1986 - Case Western Reserve University in Cleveland, Ohio creates the first “Free net” for the Society for Public Access Computing. 1987-The number of Internet hosts exceeds 10,000. 1988 – 1990 By 1988 the Internet is an essential tool for communications; however it also begins to create concerns about privacy and security in the digital world. New words, such as “hacker,” “cracker” and” electronic break-in”, are created. These new worries are dramatically demonstrated on Nov. 1, 1988 when a malicious program called the “Internet Worm” temporarily disables approximately 6,000 of the 60,000 Internet hosts. 1988 - The Computer Emergency Response Team (CERT) is formed to address security concerns raised by the Worm. 1989 - System administrator turned author, Clifford Stoll, catches a group of Cyber spies, and writes the best-seller “The Cuckoo’s Egg.” The number of Internet hosts exceeds 100,000. 1990 - A happy victim of its own unplanned, unexpected success, the ARPANET is decommissioned, leaving only the vast network-ofnetworks called the Internet. The number of hosts exceeds 300,000. 1991 - 1993 Corporations wishing to use the Internet face a serious problem: commercial network traffic is banned from the National Science Foundation’s NSFNET, the backbone of the Internet. In 1991 the NSF lifts the restriction on commercial use, clearing the way for the age of electronic commerce. At the University of Minnesota, a team led by computer programmer Mark MaCahillreleases “gopher,” the first point-and-click way of navigating the files of the Internet in 1991. Originally designed to ease campus communications, gopher is freely distributed on the Internet. MaCahill calls it “the first Internet application my mom can use.” 1991 is also the year in which Tim Berners-Lee, working at CERN in Switzerland, posts the first computer code of the World Wide Web in a relatively innocuous newsgroup, “alt.hypertext.” The ability to combine words, pictures, and sounds on Web pages excites many computer programmers who see the potential for publishing information on the Internet in a way that can be as easy as using a word processor. Marc Andreessen and a group of student programmers at NCSA (the National Center for Supercomputing Applications located on the campus of University of Illinois at Urbana Champaign) will eventually develop a graphical browser for the World Wide Web called Mosaic. 1991 - Traffic on the NSF backbone network exceeds 1 trillion bytes per month. 1992 - The first audio and video broadcasts take place over a portion of the Internet known as the “MBONE.” More than 1,000,000 hosts are part of the Internet. 1993 - Mosaic, the first graphics-based Web browser, becomes available. Traffic on the Internet expands at a 341,634% annual growth rate. 1994 - 1996 As the Internet celebrates its 25th anniversary, the military strategies that influenced its birth become historical footnotes. Approximately40 million people are connected to the Internet. More than $1 billion per year changes hands at Internet shopping malls, and Internet related companies like Netscape are the darlings of high-tech investors. The Age of the Internet has arrived. · 1994 - The Rolling Stones broadcast the Voodoo Lounge tour over the MBone. Marc Andresen and Jim Clark form Netscape Communications Corp. Pizza Hut accepts orders for a mushroom, pepperoni with extra cheese over the net, and Japan’s Prime Minister goes online at www.kantei.go.jp. Backbone traffic exceeds 10 trillion bytes per month. · 1995 - NSFNET reverts back to a research project, leaving the Internet in commercial hands. The Web now comprises the bulk of Internet traffic. The Vatican launches www.vatican.va. James Gosling and a team of programmers at Sun Microsystems release an Internet programming language called Java, which radically alters the way applications and information can be retrieved, displayed, and used over the Internet. 1996 - Users in almost 150 countries around the world are now connected to the Internet. The number of computer hosts approaches 10 million. Within 40 years, the Internet has grown from a Cold War concept for controlling the tattered remains of a post-nuclear society to the Information Superhighway. Just as the railroads of the 19th century enabled the Machine Age, and revolutionized the society of the time, the Internet takes us into the Information Age, and profoundly affects the world in which we live. Today some people telecommute over the Internet, allowing them to choose where to live based on quality of life, not proximity to work. Many cities view the Internet as a solution to their clogged highways and fouled air. Schools use the Internet as a vast electronic library, with untold possibilities. Doctors use the Internet to consult with colleagues half a world away. And even as the Internet offers a single Global Village, it threatens to create a 2nd class citizenship mongo those without access. As a new generation grows up as accustomed to communicating through a keyboard as in person, life on the Internet will become an increasingly important part of life on Earth. The evolution of the Internet can at best be described as a phenomenon. It had gone from near invisibility to near ubiquity in only a short period. The sad conclusions that many people may draw lead them to believe that since the Internet became popular overnight, it was created overnight. The ignorance of the common citizen unfortunately does no justice to the hard work and efforts of the many scientists, students, and intellectuals who collaborated and created this technological masterpiece covering the world called the Internet. Internet Working How the Internet Works The Internet is the world’s largest distributed system; it was designed and engineered for redundancy (it has an abundance of routes and connections) and resilience (it easily recovers from a mishap). The Internet is not a single company or a group of companies, nor even a single network. It is a worldwide mesh or matrix of hundreds of thousands of networks, owned and operated by hundreds of thousands of people in hundreds of countries, all interconnected by about 8,000 ISPs (Internet Service Providers). No single organization controls the Internet; not the U.N.; not the biggest ISPs; and the Internet has long since outgrown control by the U.S. government. The Internet is different from other major services. Electricity tends to be provided by a single company in each geographical area. The “last mile” of telephone service to the customer is usually owned by a single company. But in general there is more than one Internet provider in any locale, and there are usually many paths from a local provider in one area to a provider in another area. When you, the user, look at a web page through the Internet, many things happen along the way. There are various ways to get from your house or office through the “last mile” to the Internet: modem dialup, ISDN, DSL, cable modem, wireless, leased line, etc. These various technical methods may provide speeds anywhere from very slow (a few hundred bits per second) to very fast (billions of bits per second). All these access methods are onramps to the information superhighway. In order to transmit text or pictures, your data is chopped up into small packets which are routed through the Internet. But first they have to go from you to your local ISP, or the equivalent piece of the Internet inside your organization (an intranet). This local ISP is a possible point of failure. If something goes wrong at your local ISP, it may look to you like the Internet is broken. It’s not. Only one small piece of it is broken. The rest of the Internet, with its portals and stock portfolios and shops and reams of scientific data and plethora of information and people on it will not break because one ISP does. To reach a web server, your local ISP sends your packets of data to another ISP, which may send them to another ISP, or through an Exchange Point (IX) or a National Access Point (NAP) or Local Access Point (LAP) to get to another ISP. Thus your packets pass through a chain of ISPs through nodal points to reach their destination. Your packets may pass through fiber optic cables in the ground, satellites in the sky, undersea cables, or radio links. They may travel at speeds including T-1 (1.544 Mbps), T-3 (45Mbps), or faster (or slower). The Internet Protocol (IP) ties all of those links together, enabling your packets travel through the Internet. Eventually your packets arrive at the web server, and the web server sends responses back along a similar path (almost definitely not the same one). Any of these Internet providers can have problems (congestion, broken link, power outage, broken computer, etc.), which may cause the web server to seem slow or unresponsive to you. But the web server is broken only if the web server is actually broken. Problems in intervening parts of the Internet do not break the web server, which may well be accessible to other people, and may become accessible to you as soon as the various Internet providers route your traffic around problems. Much rerouting in the Internet is dynamic, and happens automatically. (Imagine you are driving up the California coast and come to a sign that says that there has been a mudslide. You drive inland, north on another road, perhaps rejoining the coastal highway again. You have changed your route dynamically.) Some rerouting isn’t automatic. In particular, the biggest ISPs, frequently called backbones, cover vast geographical areas and carry large proportions of the Internet’s traffic. A failure in a backbone or in one of the major interconnection points between them can affect many Internet users. And such a problem may take some time to be resolved, as the biggest ISPs often prefer to manually examine changes in major routes before implementing them. But longstanding observation of the Internet indicates that “some time” is normally at most few hours, even in the face of the biggest problems. Internet providers use the same methods for routing packets for electronic mail or file transfers or remote login or voice or video. People tend to be quicker to notice slowness in accessing web pages, so we have used accessing a web server as an example. There are other key pieces of the Internet, most notably the root name servers. Name servers translate domain names, such as www.ripe.net, into the IP addresses, such as 193.0.0.195, that are used by the Internet protocols in carrying your packets through the Internet. The root name servers handle the most basic part of that translation, which is finding name servers for the top level domains (TLDs), such as NET, COM, ORG, EDU, GOV, FR (France), JP (Japan), AU (Australia), or PE (Peru). The root name servers are widely spaced in both geography and in Internet topology, so that a failure in one cannot readily affect another. The root name server operators have also cooperated in extensively testing their software, hardware, and capacities, and they all know how to reach each other in case they perceive problems. The rest of the Domain Name Service (DNS) is distributed among hundreds of thousands of name servers for the various domains. For example, there are name servers for ORG, and then there are name servers for MIDS.ORG. Every domain is supposed to have at least two independent name servers, and most do (another instance of redundancy). In any case, a failure in a single name server may make a particular domain temporarily inaccessible, but it will not affect the Internet at large. The decentralization of the Internet is one of its biggest advantages and one of its most basic features, designed into its protocols from the beginning and tested in practice over many years. If one piece breaks, that doesn’t mean the Internet is broken. And decentralization requires cooperation, so the various ISPs and IXes and the like are accustomed to cooperating with one another to fix and prevent problems. It is this decentralization and cooperation that has permitted the Internet to grow faster for longer than any other technological phenomenon in history. It is important for you, the user, to understand how decentralization makes the Internet work, so that you will know that the Internet is actually very hard to break. Internet Services Some of the most popular Internet services include electronic mail (email), the World Wide Web (WWW), Chat, Internet News, File Transfer Protocol (FTP), and Telnet. Electronic mail (e-mail) E-mail is the most popular service on the Internet. You can use it to send messages to any user connected to the Internet. World Wide Web (WWW) The World Wide Web, or the Web, is a term used to describe the interlinked collection of hypertext documents and multimedia content available on the Internet. Hypertext documents are files that have been formatted for use on the Internet. You use a Web browser, such as Microsoft Internet Explorer, to search for, locate, view, and download information from the Internet. Chat Chat programs allow you to participate in a real-time conversation with two or more people on the Internet. Internet News Internet News is a service that hosts electronic discussion groups through which participants can share information and opinions. A news client, such as Microsoft Outlook® Express, can then be used to access these groups. File Transfer Protocol (FTP) FTP is a service that includes a server for transferring files from the server to a client computer. Users can download files from the FTP server by using an FTP client utility. Telnet Telnet offers a way to remotely log on to a computer and work on that computer. By logging on to this computer remotely, users can access services or resources that they may not have on their own workstation. Internet Access Methods Connections to the Internet can be described in four basic categories: dialup, proxy, direct and leased. A dialup connection A dialup connection is attained through a modem or similar device. The connection typically provides between 2400 bps (bits per second) and 28,800 bps throughputs, which is usually more than adequate for e-mail and for running processes on the remote host. While this type of connection is usually adequate for line-oriented access, it is not suitable for full-screen programs. For instance, utilities such as Mosaic expect to be able to address the full screen of a machine that is directly connected to the internet. To make full use of many of the current Internet resources, then, a more advanced connection is required—at minimum, a proxy connection. A proxy connection A proxy connection is also typically made through a modem, but it has special provisions that enable full Internet access. SLIP (Serial Line IP) and PPP (Point-to-Point Protocol) are two examples of such provisions (both discussed later in this chapter). Tools such as FTP, Gopher and Mosaic are thereby available for use just as if the connection were directly on the Internet. Direct connections Direct connections are obtained when the machine being used has a dedicated circuit to the Internet. This can still be a remote connection, but it has the full functionality of a directly connected machine. A good example is ISDN (Integrated Services Digital Network), which is discussed later in this chapter. Leased line Lastly, the leased line is a circuit leased from the local telephone company that provides a permanent address on the Internet. The advantage of a permanent address is that it that enables services such as FTP or Gopher to be set up. The leased line varies in throughput from 9600 bps to 45,000,000 bps (45 Mbps). Internet Service Provider ISP definition An Internet Service Provider, or ISP, is a company that provides its customers with access to the Internet. Customers may connect to their ISP through dialup (telephone), broadband (including DSL, ISDN and cable modem services), or wireless connections. There are countless national and regional ISPs, and a great many websites exist to help you locate the best one for you. There are many different ISP’s which provide a broad variety of services at a broad variety of prices. An ISP has the equipment and the telecommunication line access required to have a point-of-presence on the Internet for the geographic area served. The larger ISPs have their own high-speed leased lines so that they are less dependent on the telecommunication providers and can provide better service to their customers. Among the largest national and regional ISPs are AT&T WorldNet, IBM Global Network, MCI, Netcom, UUNet, and PSINet. ISPs also include regional providers such as New England’s NEAR Net and the San Francisco Bay area BAR Net. They also include thousands of local providers. In addition, Internet users can also get access through online service providers (OSP) such as America Online and CompuServe. The larger ISPs interconnect with each other through MAE (ISP switching centers run by MCI WorldCom) or similar centers. The arrangements they make to exchange traffic are known as peering agreements. There are several very comprehensive lists of ISPs world-wide available on the Web. An ISP is also sometimes referred to as an IAP (Internet access provider). ISP is sometimes used as an abbreviation for independent service provider to distinguish a service provider that is an independent, separate company from a telephone company. The Types and Functions of Modems The Origin of Modems The word “modem” is a contraction of the words modulatordemodulator. A modem is typically used to send digital data over a phone line. The sending modem modulates the data into a signal that is compatible with the phone line, and the receiving modem demodulates the signal back into digital data. Wireless modems convert digital data into radio signals and back. Modems came into existence in the 1960s as a way to allow terminals to connect to computers over the phone lines. A typical arrangement is shown below: In a configuration like this, a dumb terminal at an off-site office or store could “dial in” to a large, central computer. The 1960s were the age of time shared computers, so a business would often buy computer time from a timeshare facility and connect to it via a 300-bit-per-second (bps) modem. A dumb terminal is simply a keyboard and a screen. A very common dumb terminal at the time was called the DEC VT-100, and it became a standard of the day (now memorialized in terminal emulators worldwide). The VT-100 could display 25 lines of 80 characters each. When the user typed a character on the terminal, the modem sent the ASCII code for the character to the computer. The computer then sent the character back to the computer so it would appear on the screen. When personal computers started appearing in the late 1970s, bulletin board systems (BBS) became the rage. A person would set up a computer with a modem or two and some BBS software, and other people would dial in to connect to the bulletin board. The users would run terminal emulators on their computers to emulate a dumb terminal. IP Addressing What Is an IP Address? Each TCP/IP host is identified by a logical IP address. A unique IP address is required for each host and network component that communicates by using TCP/IP. The IP address identifies a system’s location on the network in the same way that a street address identifies a house on a city block. Just as a street address must identify a unique residence, an IP address must be globally unique and have a uniform format. Network ID Each IP address defines the network ID and host ID. The network ID identifies the systems that are located on the same physical segment. All systems on the same physical segment must have the same network ID. The network ID must be unique to the internet work. Host ID The host ID identifies a workstation, server, router, or other TCP/IP host within a segment. The address for each host must be unique to the network ID. Network ID and Host ID Each IP address is 32 bits long and is composed of four 8-bit fields, called octets. Octets are separated by periods. The octet represents a decimal number in the range 0–255. This format is called dotted decimal notation. The following is an example of an IP address in binary and dotted decimal formats. Internet Domains In the old days, where the Internet barely had 200 hosts, every host knew the address of every other host on the Internet. Every host also associated a human-readable name with every other host’s IP address so that the user didn’t have to remember all those numbers. Now the Internet has millions of hosts connected to it, however, so keeping track of every host on every computer isn’t just impractical, it’s impossible. You certainly can access a host by its IP address. For example, to access my host, you’d use 206.50.127.46. To access Macmillan’s host, you’d use 206.246.150.10. Why use an IP address, however, when you can use a domain name instead? A domain name is a unique, human- readable name for a host on the Internet. Domain names are case sensitive, by the way. For example, honeycutt.com, mcp.com, and microsoft.com are examples of domain names. Domain names are divided into parts with a period, just like an IP addresses. Whereas an IP address gets more specific as you look from left to right, domain names get more specific as you look from right to left. In general, domain names follow this format: hostname. Second-level. first-level First-level. The first-level domain is the least specific. You’ll see firstlevel domains like com and uk, which represent the type of organization or country in which the host belongs. Table 2.1 describes some of the first-level domains that are typical on the Internet. First-level domains are also called zones or top-level domains. Second-level The second-level domain identifies the organization that owns or operates the network to which the host is attached. Every organization that has a network attached to the Internet has registered their second-level domain. The name usually represents the company’s name or trade. For example: microsoft.com, honeycutt.net, and whitehouse.gov. Host-name The host-name identifies the host on the network represented by the first- and second-level domains. The host-name isn’t registered because the network on which the host resides worries about routing traffic to the host based upon its name. That is, the only information that the Internet’s routers need to route traffic to the host is the first- and second-level domains. The host’s network worries about routing traffic to the host given its host-name. First-Level Domain Names Name Description .com Commercial and for-profit organizations .edu Universities & Education Organization .gov Federal government agencies .mil U.S. military sites .net Internet infrastructure and service providers .org Miscellaneous and non-profit organizations TCP/IP Protocol TCP/IP (Transmission Control Protocol/Internet Protocol) is the basic communication language or protocol of the Internet. It can also be used as a communications protocol in a private network (either an intranet or an extranet). When you are set up with direct access to the Internet, your computer is provided with a copy of the TCP/IP program just as every other computer that you may send messages to or get information from also has a copy of TCP/IP. TCP/IP is a two-layer program. The higher layer, Transmission Control Protocol, manages the assembling of a message or file into smaller packets that are transmitted over the Internet and received by a TCP layer that reassembles the packets into the original message. The lower layer, Internet Protocol, handles the address part of each packet so that it gets to the right destination. Each gateway computer on the network checks this address to see where to forward the message. Even though some packets from the same message are routed differently than others, they’ll be reassembled at the destination. TCP/IP uses the client/server model of communication in which a computer user (a client) requests and is provided a service (such as sending a Web page) by another computer (a server) in the network. TCP/IP communication is primarily point-to-point, meaning each communication is from one point (or host computer) in the network to another point or host computer. TCP/IP and the higher-level applications that use it are collectively said to be “stateless” because each client request is considered a new request unrelated to any previous one (unlike ordinary phone conversations that require a dedicated connection for the call duration). Being stateless frees network paths so that everyone can use them continuously. (Note that the TCP layer itself is not stateless as far as any one message is concerned. Its connection remains in place until all packets in a message have been received.) Many Internet users are familiar with the even higher layer application protocols that use TCP/IP to get to the Internet. These include the World Wide Web’s Hypertext Transfer Protocol (HTTP), the File Transfer Protocol (FTP), Telnet (Telnet) which lets you logon to remote computers, and the Simple Mail Transfer Protocol (SMTP). These and other protocols are often packaged together with TCP/IP as a “suite.” Personal computer users usually get to the Internet through the Serial Line Internet Protocol (SLIP) or the Point-to-Point Protocol (PPP). These protocols encapsulate the IP packets so that they can be sent over a dial-up phone connection to an access provider’s modem. Protocols related to TCP/IP include the User Datagram Protocol (UDP), which is used instead of TCP for special purposes. Other protocols are used by network host computers for exchanging router information. These include the Internet Control Message Protocol (ICMP), the Interior Gateway Protocol (IGP), the Exterior Gateway Protocol (EGP), and the Border Gateway Protocol (BGP). The Intranet An intranet shares most of the characteristics of the Internet, but in at least one way, it’s fundamentally different. And just as the Internet has had profound effect on how we communicate, intranets have transformed the business world as well. Both Fortune 500 companies and small businesses have implemented this infrastructure, improving productivity while reducing costs. Just what is an intranet? Think of it as a mini-Internet designed to be used within the confines of a company, university or organization. What distinguishes an intranet from the freely accessible Internet is that intranets are private. Evolution of WWW Ever since the Internet merged as an emblem in our mind, the World Wide Web (WWW) has been exploding into all the aspects of our work, studies and leisure life. Within the employment market, jobs requiring knowledge of the Web, Internet and e-Commerce have been most in demand from both employer and employee’s perspectives. As an employer or employee coping with the ever changing IT work environment, you should have a fair understanding of the history, development, capabilities and the future of WWW. In a series of informative articles, I will introduce all issues associated with the World Wide Web from the employment perspective. Here I begin with the 30-year evolution of WWW to preface the series. Client/Server computing Increasing numbers of users have to share data. Programs are divided into two parts: client and server. 1. Client applications that run on local machines allow users to manipulate centralized data. 2. Server applications that run on centralized machines coordinate sharing of the data amongst many users. Middleware software provides transparency between servers and clients in three-tier client/server systems. The Internet The attempts to connect all private and public networks are successful with the appearance of the Internet. Internet Protocol (IP) becomes a de-facto standard network protocol of exchanging data between various networks. Transport Control Protocol (TCP) becomes a de-facto standard transport protocol on top of IP. Their combination is referred to as the TCP/IP standard. The World Wide Web WWW originated as a framework for electronic publishing of hypertext. 1. HTML – Hypertext Markup Language. 2. HTTP – Hypertext Transfer Protocol. The scope of content published on the Web pages expands daily and includes text, graphics, sound and video. A Web browser is becoming a new operating system for many users. Other traditional network applications like email, file transfer, telnet/remote login have been incorporated under the same browser roof with the Universal Resource Locator (URL). New business opportunities have emerged in electronic publishing and commerce. New technologies like search engines, agents, etc., mix with not-so-new ones like data mining to address arising challenges. Any user can access any computer anywhere in the world using the Internet. Connecting to Internet How to Connect to the Internet Before you can connect to the Internet and access the World Wide Web, you need to have certain equipment. In brief, you must have a computer (preferably running an up to- date operating system); a modem and access to a telephone line or a local area network (LAN) that is in turn connected to the Internet; and connection software that will allow you to establish an account with a service provider and access the Internet. A modem is not needed when accessing the Internet through a LAN The Right Hardware To operate most of the current Web browsers and on-line services, you should have an IBM PC/PC equivalent, UNIX workstation, or Apple Macintosh computer with at least 8 megabytes (MB) of random access memory (RAM) and 10 MB of free disk space. If you are unsure of how much RAM and disk space your computer has, consult your user’s manual. For best results, use a PC with a 486 or Pentium microprocessor; or a Macintosh with a 030, 040 or PowerPC microprocessor. It is possible to connect to the Internet using a computer other than an IBM PC, Macintosh or UNIX workstation, though the access software available for such machines is limited. If you are accessing the Internet outside of a LAN environment, you will need a modem that will connect you with other computers and interpret the data being sent back and forth. Most any modem that is compatible with your computer will do, though the higher the kilobits per second (kbps) rate of your modem, the faster it will transmit data. Modem speed is an important consideration when accessing sites on the Web that contain lots of digitized data. In general, your modem should transmit data at 14.4 kbps or faster to give you optimum performance on the Web. If you are looking to purchase a modem, buy the fastest model you can afford. You must also have access to a live telephone line. Most modems accept the same jacks as do ordinary household telephones, allowing you to connect your modem to a wall jack using standard phone cord. Some cable TV providers have begun offering Internet connections via cable. Such connections provide much faster transmission speeds than standard phone lines, though you will need a special modem that allows you to link your computer with the cable. If you are interested in a cable Internet connection, contact your local cable operator to see if the service is available in your area. You can also connect to the Internet through a LAN with Internet access. If you are unsure as to the capacities of your LAN to do this, contact your site’s systems administrator The Right Software For best results, make sure that your computer is running the most upto-date operating system that it can handle. If you have an IBM PC/PC compatible computer, it should be running Microsoft Windows version 3.1, Windows NT, Windows 95 or OS/2. If you have a Macintosh, it should be running System 7 or higher. To make your connection complete, you will need connection software that allows your computer to dial into an Internet access provider, establish an account, and work with the data in a straightforward manner. Many access providers will give you software that will allow you to access their systems using an all-in-one custom interface. Others may give you a collection of separate software packages that can be used together. But whatever software they provide, be sure that it is compatible with your computer and operating system before attempting to use it. Some Internet access providers may allow you to establish a serial line interface protocol (SLIP) or point-to-point protocol (PPP) connection, either of which essentially makes your computer a part of the Internet. Unlike many standard dial-up software packages, a SLIP/PPP connection allows you to run independent software packages such as Web browsers, either one at a time or simultaneously. The Browser As you surf the Web, you will come across sites that state, “This site is best viewed with…” and then name a particular browser. Many will even provide a link to a site where you can download the specified browser. Sites make these recommendations because some browsers use special protocols, allowing site creators to offer extra features beyond the standard capabilities of hypertext markup language (HTML). Chief among these browsers are Netscape Navigator and Microsoft Internet Explorer. Your Internet service provider will most likely give you a choice of browsers so try out a couple, and use the browser that best suits your needs. Connection Options Until recently, the two primary methods of accessing the Internet were through a network connection, allowing users of local area networks (LANs) to go online through their school or workplace systems, and dial-up connections through a modem and phone line. However, new connection options allow for greater speeds and flexibility, while keeping costs to a minimum. The following are some of the newer connection options that you might want to investigate: · Cable Internet—these systems allow your computer to connect to the Internet through the same cable that carries your TV signal. Monthly service charges are usually not much more than standard modem connection costs, but you have to rent or purchase a “cable modem.” Additionally, your computer will need an Ethernet card (a special circuit board that allows for network connections). Not all cable service operators offer this service; call your local operator for more information. Web Browsers The World Wide Web (WWW), or Web, is the portion of the Internet that provides links to graphical content. The Web has developed into a network of interactive documents that you can easily locate and read using various Web browsers, such as Internet Explorer. A Web browser is a client application that enables the client com putter to gain access to a Web server or other server, such as an FTP server, running on the Internet. Web browsers can display text files and various graphic and multimedia format files. A browser also interprets and displays documents. Web Servers Web server is a program that, using the client/server model and the World Wide Web’s Hypertext Transfer Protocol (HTTP), serves the files that form Web pages to Web users (whose computers contain HTTP clients that forward their requests). Every computer on the Internet that contains a Web site must have a Web server program. Two leading Web servers are Apache, the most widely- installed Web server, and Microsoft’s Internet Information Server (IIS). Other Web servers include Novell’s Web Server for users of its NetWare operating system and IBM’s family of Lotus Domino servers, primarily for IBM’s OS/390 and AS/400 customers. A client computer connects to the Internet or an intranet by using a Web browser to find information stored and organized on a Web server. A Web server is a computer that uses TCP/IP to send Web page content to client computers over a network. A Web server communicates with clients by using an appropriate protocol, such as HTTP or HTTPS. The terms Web server and HTTP server are synonymous, because URLs identifying data on a Web server begin with http. For example, the Microsoft Web site is http://example.microsoft.com/. Every Web server has an IP address and perhaps a domain name. For example, when you enter the URL http://example.microsoft.com/webpage.htm in your Web browser, it sends a request to the Web server with the domain name microsoft.com. Then the Web server locates and retrieves the page ms.htm, and sends it to your browser. Web servers often come as part of a larger package of Internet- and intranet-related programs for serving e-mail, downloading requests for File Transfer Protocol (FTP) files, and building and publishing Web pages. Considerations in choosing a Web server include how well it works with the operating system and other servers, its ability to handle server-side programming, security characteristics, and publishing, search engine, and site building tools that may come with it. Proxy Servers Most home and small office networks use a dial-up or modem network connection to an ISP, which in turn connects them to the Internet. The ISP assigns a single IP address to each network for connecting to the Internet. In addition, each computer in a network requires an IP address for Internet connection. Rather than using separate IP addresses for each computer, it is more cost-effective to use a single IP address for multiple computers. A proxy server is a firewall component that enables you to connect multiple computers in a network to the Internet by using a single IP address. Proxy servers have two main functions: to improve network performance and filter client requests. Domain Name Server The Domain Name System (DNS) is a global network of servers that translate host names like www.internic.net into dotted numerical IP (Internet Protocol) addresses, like 198.41.0.6 A DNS server is just a computer that’s running DNS software. DNS software has two parts: 1. The actual name server 2. A resolver. The name server responds to browser requests by supplying name-toaddress conversions. When it doesn’t know the answer, the resolver will ask another name server for the information. When you type in a URL, your browser sends a request to the closest name server. If that server has recently had a request for the same host name, it will locate the information in its cache and reply. If the name server is unfamiliar with the domain name, the resolver will ask another nameserver. If that doesn’t work, the second server will ask yet another - until it finds one that knows. Once the information is located, it’s passed back to your browser, and you are sent to the web site for the URL you entered. Usually this process occurs quickly, but sometimes it takes several seconds. Occasionally, you will get a dialog box that says the domain name doesn’t exist, even though you know it does. This happens because of delays in one name server replying to another, and your computer times out, dropping the connection. Often, if you try again, you will get to the web site you are looking for on the second try. This is because the nameserver with the information has had enough time to reply, and your name server has now stored the information in its cache. Hypertext Hypertext is a text which contains links to other texts. The term was invented by Ted Nelson around 1965. Hypertext is therefore usually non-linear (as indicated below). Hypertext allows movement through a document in a non-linear fashion. As such, it is a departure from a book and other “written” material. The user can “navigate” through the use of links. These links may be selected through a keyboard, a mouse, a touch screen or some other input device. In all cases, a microprocessor is used. Hypertext documents are prepared using an authoring tool. The most common authoring tool is probably Hypertext Markup Language (HTML) However; there are other well known authoring tools such as Author ware and Toolbox. Standard General Markup Language that can also be used. Technically speaking hypertext is a link you click on to get from one page to another when surfing the internet (or an intranet). The pictures and phrases that make up the links are called hypertext links. Any time you click on something on a web site you are actively using hypertext. The hypertext we want to look at here is a type of electronic genre for writing. We want to give you some ideas of how you can use hypertext in the classroom and as a publishing medium. Hyperlinks A hyperlink is a reference to another location within the existing HTML document or in a new HTML document. The data of the HTML document or object can be stored in file system file server on the Internet (referred to by URLs), or any arbitrary location that can be referenced How a hyperlink is presented to the user is up to the hyperlink container and the context of the hyperlink. It is common for hyperlinks to be presented as colored, underlined text, as hotspot regions on an image, or as pushbuttons. However, there are no user interface requirements limiting the presentation of hyperlinks, although guidelines suggest that they should be made obvious-via coloring, underlining, or by changing the cursor or displaying tool tips when mouse over occurs. A hyperlink is the same thing as a link. A link can be a picture or text or just about anything on a web page. When something is a link, it simply means that left clicking on it will lead you to a different place on the internet. This might mean that you will be transferred to another page on the same web site. Or, it might mean that you are transferred to a different site altogether. When a link is embedded in text, the words composing the link are usually a different color from the majority of text and most of the time, they are underlined. URL (Universal Resource Locator) Although a domain name provides a convenient way of referring to a specific computer on the Internet, you rarely want to just connect to a computer. More often, you want to retrieve information from a file on the computer. To access a file on a computer connected to the Internet, you must know the path to that file, known as its address. The addressing system developed for this purpose is called a Uniform Resource Locator (URL). What is a Domain Name? Domains are the data that the Internet uses to identify specific “lots” within the network. In their raw form, domains are numeric. I’m sure you’ve seen this reflected in numeric URLs. Domain names are alphanumeric overlays to the numeric component of a given domain. Essentially, they are the name of the server on which the information resides. Systems Administrators get the names from the Interknit how a name will be implemented are going to be up to you and the server situation you are involved with. But, to some, having a domain name is as much a part of their marketing strategy as other forms of advertisement. Domain Name Parts Domains have two primary parts: the name and the suffix. Names can be almost anything you want, although there are some character restrictions. Typically, any combination of letters and numbers can be used to create the name. This is followed by a suffix, which determines the type of organization under which you register. General suffixes include .com—Commercial organization (very common on the Web these days!) .edu—Educational organization .gov—Government institution .mil—Military institution .net—Network .org—Organization There are also country codes that fall into the suffix section of a domain. Some examples include .jp—Japan .uk—Great Britain .mx—Mexico Search Engines What are Search Engines? Search engines are huge databases of web page files that have been assembled automatically by machine. There are two types of search engines: · Individual. Individual search engines compile their own searchable databases on the web. · Meta. Met searchers do not compile databases. Instead, they search the databases of multiple sets of individual engines simultaneously It is a program that searches documents for specified keywords and returns a list of the documents where the keywords were found. Although search engine is really a general class of programs, the term is often used to specifically describe systems like Alta Vista and Excite that enable users to search for documents on the World Wide Web and USENET newsgroups Home Page What is a Home Page? For a Web user, the home page is the first Web page that is displayed after starting a Web browser like Netscape’s Navigator or Microsoft’s Internet Explorer. The browser is usually preset so that the home page is the first page of the browser manufacturer. However, you can set it to open to any Web site. For example, you can specify that “http://w.yahoo.com” or “http://myweb.com” be your home page. You can also specify that there be no home page (a blank space will be displayed) in which case you choose the first page from your bookmark list or enter a Web address. For a Web site developer, a home page is the first page presented when a user selects a site or presence on the World Wide Web. The usual address for a Web site is the home page address, although you can enter the address (Uniform Resource Locator) of any page and have that page sent to you. Web page images Unless you are using a very new version of Internet Explorer as your browser, saving a Web page will not include any images or animations that are on the page - they are separate files. If the images on the Web page are an important part of the content you wish to save to use offline, you must save the images independently. To do so, right click the image (PC) or hold the mouse down on the image (Mac) and select Save Picture as or Save Image As from the pop-up menu. (If this option is not present in the pop-up menu, it is not a standard image file that you can use offline - you are out of luck.) You will be prompted with the Save dialog box as usual. It would be best to save the file with the name and file type that is presented. If you have saved the image file in the same location as the Web page HTML file, there is a chance that you will see the image when you open the Web page in your browser from your hard drive. If you do not see the image, the Web page’s author must have used a different file hierarchy - you will have to view the image separately from the Web page. Internet Explorer 5.0 will give you an option to save the “Web page complete”, which means it will save the page’s images with the HTML file for offline viewing. E-mail Electronic mail, or e-mail as it is more commonly known, is a paperless method of sending letters, notes and messages from you to someone else or even many people at the same time via the Internet. Electronic mail is very fast compared to the post office. Your messages usually only take seconds to arrive at their destination. You can send messages anytime and the message will be available whenever the other person wants to look at it - even in the middle of the night. But perhaps the biggest advantage to using e-mail is that it is cheap, especially when sending messages to other states or countries. Today, it costs the same to send e-mail to someone around the corner as it does to send the message to a friend in a foreign country. Advantages of Electronic Mail System There are many remarkable features that make electronic email far ahead of other telecommunication technologies. Back in 1992, there were only 2% of Americans use electronic mail systems in the United States. The percentage went up to 15% today. It went up seven times within 5 years, according to a survey by consultants Forrester. Forrester also estimated that within the next five years more than half of the American population will be using e-mail. The lists below are few major advantages that encourage people to use electronic mail over other similar communication tools. · It can send pictures, sounds, spreadsheet, and long document. It costs users nothing - probably just the cost of a local phone call. · It is fast. It can be arrived anywhere in the world within a few minutes. · It makes clear and concise communication, avoids the risk of verbal misunderstanding. Electronic mail is actually a wonderful tool that helps individuals and companies work faster and smarter when productivity and efficiency is the key. All of these advantages have helped employers to choose electronic mail system as their major communication tool for internal and external use. Protocols used Common Internet protocols that enable you to access the Internet are Hypertext Transfer Protocol (HTTP), HTTP Secure (HTTPS), File Transfer Protocol (FTP), Simple Mail Transfer Protocol (SMTP), and Network News Transfer Protocol (NNTP). In addition, Hypertext Markup Language (HTML) and Dynamic HTML (DHTML) specify the formats of pages displayed on the Web. · HTTP HTTP is a convention for sending messages from a server to a client by using TCP/IP. HTTP communications are in plain text and not encrypted. · HTTPS HTTPS enables you to make a secure Web server connection by using Secure Sockets Layer (SSL). SSL is an encryption technology that enables a secure connection between a server and a client. The URLs for Web pages that require an SSL connection start with https://. · FTP FTP enables you to transfer files between two computers on a network. · SMTP SMTP enables you to send e-mail over the Internet. · NNTP NNTP enables you to post, distribute, and retrieve messages on Internet and intranet newsgroups. · HTML HTML is the standard language for creating and formatting Web pages. HTML defines how text appears when viewed in a Web browser. Mail Server A mail server is a computer, or a software package, that provides a mail service to client software running on other computers. There are main two types of mail servers. POP3 (Incoming) E-mail Server Post Office Protocol 3 is the most recent version of a standard protocol for receiving email. POP3 is a client/server protocol in which e-mail is received and held for you by your Internet server. Periodically, you (or your client email receiver) check your mail-box on the server and download any mail. POP3 is built into the Netscape and Microsoft Internet Explorer browsers. POP3 accounts allow clients to have a private e-mail address where they can exchange email with anyone they wish at anytime. Each POP3 email account comes with its own login and password. The login is set by the characters preceding the at sign “@” in the e-mail address. The password is determined by the client when the POP3 account is setup. SMTP (Outgoing) E-mail Servers The ability to provide Email services to clients includes two critical functions: SMTP and POP3. Together, they provide the means for clients to send out-going mails and check for new incoming mail, respectively. SMTP service is the side of Email that allows clients to send out-going E-mail messages to any valid Email address. The SMTP server performs two basic but important functions. First, it verifies that anyone attempting to send outgoing E-mails through the SMTP server has the right to do so. Secondly, it sends the out-going mails and if undeliverable, sends the message back to the sender. You need to configure your Email client so that it knows what SMTP server to use for sending outgoing E-mail messages. In order to send mails through the proper SMTP servers, configure your e-mail client to access the SMTP (Outgoing Mails) Server: yourdomain.com. Mail Addresses Definition of Email Address and ID Terms University Email Address Address appearing in any public paper or electronic directories. This address is used to protect the User ID from public view. Default format of this address is ‘first name’.’ last name’@uky.edu. The portion of this address before the ‘@’ may be modified by the owner. Mailbox Email system address to which email is redirected from the University Email Address, stored and read by a user. Default format of this address is ‘User ID or other’@’email system identifier’.uky.edu. The ‘email system identifier’ is not included in U-Connect accounts. User ID: This ID is used in conjunction with a password to permit a user to log into an email system and access email in their mailbox. Common Features in Netscape Communicator and Internet Explorer Internet Explorer and Netscape Communicator Internet Explorer has migrated to the forefront as the preferred browser because of the various applications used across the Internet by the University System. Such programs as the PeopleSoft applications and various medical programs used in the hospital enterprise require that Internet Explorer be used. One thing to note is that Internet Explorer is installed by an automated process that is established by ITS. For that reason, some functions are not accessible. For example, endeavoring to change some the Options in Internet Explorer will be impossible because the fields are grayed-out. The centralized installation will also force some characteristics onto your workstation that have proven to be an inconvenience to users. The only resolution is to make Internet Explorer your default browser. The instructions for doing this are provided below. Unfortunately, Internet Explorer is essentially a proprietary Microsoft product and is not fully compliant with many of the international programming standards used at many web sites. Netscape is often required to access some of the features used at web sites. Until the compatibility issues are resolved, both browsers will need to be supported and provided to users upon request. The discussions presented below are frequent issues for users and support personnel. IT support will usually provide any assistance that is needed to resolve compatibility issues between Internet Explorer and Netscape, but if help is not immediately available the information below may prove useful. Internet Explorer How to Make Internet Explorer Your Default Browser Follow these steps: Click on the Start button Select Settings Select Control Panel Select Internet Options Select the Program tab Check the box at the base of them window labeled “Internet Explorer should check to see whether ....” This usually does the trick. The next time Internet Explorer is activated, it should present a query of whether you wish it to be your default browser. Testing, however, has shown that this does not always work. Conflicts between Internet Explorer and Netscape Communicator A recent update to Internet Explorer apparently generated a rash of lockups whenever users attempted to open Netscape Communicator. Regardless of what Microsoft says under oath, Internet Explorer is installed and updated by Microsoft in a manner that seizes control of the Internet browser functions. This causes considerable confusion for users and generates considerable cost in supporting Netscape. As a consequence, the best solution is to let Internet Explorer be your default browser and to install Netscape only if it is necessary to utilize specific web pages. Step#1, making Internet Explorer your default browser, is discussed above. This usually works but there are cases where it does not work. If it fails, proceed to Step #2. Step #2 is to uninstall the Netscape program. This will clear out all remnants of the Netscape program. To do so, follow these steps: Make certain all Internet browsers are closed. Go to the Department Applications/Setups/Applications menu. Click on the item titled “Netscape Communicator 4.75 Pre-Install.” Running this program will backup your personal settings for Netscape and clean out all Netscape program files and registry settings. Re-start your PC. After logging back onto the network, open Internet Explorer. If it asks for you to make it the default browser, click “Yes.” To test how Internet Explorer will work, you may wish to bring up an email message that listed a website, click on that web site and see if Internet Explorer is presented automatically. Step #3 is necessary only if you wish to have Netscape re-installed. Make certain that all Internet browsers are closed. Return to the Department Applications/Setups/Applications menu. Run the item titled “Netscape Communicator 4.75”. This should re-load a clean set of files for Netscape and refresh the registry. Open Netscape. A “profile manager” will be presented. Select “Default” and then press the “Start Communicator” button. “Default” is the standard settings used by Netscape that accesses your personal settings located in your personal directory on the server. Importing Netscape Bookmarks A common problem with moving to Internet Explorer is incorporating the bookmarks you use in Netscape. This is fairly easy to do. Follow these steps: Open Internet Explorer Select the “File” menu. Select “Import and Export” A window will be presented explaining what you can do with this utility. Click the “Next” key. Select “Import Favorites.” Click the dot that says to Import from File or Address. File in the blank with the following: J:\Netscape\bookmark.htm For the destination, select the folder that has your login ID on it. Once the installation is complete your bookmarks will be imported into the folder under your login ID. Managing the Favorites Folder The Favorites Folder in Internet Explorer is, unfortunately, a hodgepodge of functions that could prove somewhat confusing. The oddity about Internet Explorer is that it is the only program where personal settings do not “roam.” In other words, the Favorites folder does not automatically copy to your personal directory on our server and if you move to a different computer your bookmarks will be missing. The following solutions have been employed to solve that riddle. · First, some of the folders are imported automatically from ITS. Most of these folders will pertain to commonly used University Hospital web sites. Special attention should be provided to the folder titled “University of Missouri Healthcare — Resources.” In it you will find several websites that will provide useful services · The Department supplies an additional folder with your login ID. This is where you should install your personal bookmarks. On a daily basis a program is executed that will endeavor to update your personal bookmarks to your personal directory. The only bookmarks updated, however, are those which reside under your ID. Feel free to remove folders that belong to other people. Their bookmarks should be backed up into their personal directories. Research has been completed and testing will commence in late October that will integrate the Favorites list into your personal profile. If tests prove successful, management of Favorites should be much easier and more intuitive. Web Design Concerns File Names Web page editors are rather familiar with creating “hotlinks” to other documents. You may wish to note, however, that Microsoft’s intuitive “features” that are often included with Internet Explorer and other web design tools can often create some problems with your final web document. One particular area is file naming. The Internet is based on UNIX, a network operating system. From UNIX, an internationally agreed standard of programming was devised to make it possible to read documents, tables, and images on any computer in the world. That standard was called HTML. That standard does not permit spaces in file names. For example, if you create a document in Microsoft Word and title it “Goals for 2001”, the only thing that HTML or UNIX will read is “Goals”. The result is a failed hotlink. To correct that problem, you must label the file as “Goals_for_2001”, replacing the space with an underscore. Writing effective Mail Messages E-mail is a prized tool for the small entrepreneur. It allows you to communicate quickly and frequently with your customer. It doesn’t matter that your competitor can afford a fancy logo and expensive stationery. E-mail puts you on an even footing. Without graphics or engraving to enhance your message, what you say and how you say it matters even more than in print communication. But because e-mail is so easy to send, and because as a harried owner of a small business you feel pressured to respond immediately, you often dash off a response on the fly. How many times have you clicked on “send” and then remembered a couple of points you forgot to mention? Or did you send a rambling message, giving your client the task of sorting it out? Did you think your spelling didn’t matter? After all, “it’s only e-mail!” It matters a lot. Your well-heeled competitor has the stature of his organization to back him up. His misspellings will be chalked up to “too busy to spell check.” Your misspellings and unorganized messages will call your competence into question. Does your inattention to spelling reflect a similar disregard for customer service? If your message is ill-conceived, can your product be any better? When you write e-mail messages, remember your client will judge you by what you say and how you say it. Don’t let your writing give your customers a reason to turn to your competitor. Here are some guidelines to enable you to write e-mail like the Fortune 500 pros. NUMBER THE NUMBER SYSTEMS The reason that "hex" and octal are popular in computing is that it's easy to translate to and from the binary system that computers really use. People use decimal primarily because they have ten fingers, but it's just not that convenient to switch back and forth from 10011010010 to 1234. It IS convenient to convert to 4D2 (hex) or 2322 (octal). The numbers from decimal 0 through 15 in decimal, binary, octal, and hexadecimal form are listed below. DECIMAL BINARY OCTAL HEXA -DECIMAL 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 1 10 11 100 101 110 111 1000 1001 1010 1011 1100 1101 1110 1111 0 1 2 3 4 5 6 7 10 11 12 13 14 15 16 17 0 1 2 3 4 5 6 7 8 9 A B C D E F Binary Binary describes a numbering scheme in which there are only two possible values for each digit: 0 and 1. The term also refers to any digital encoding/decoding system in which there are exactly two possible states. In digital data memory, storage, processing, and communications, the 0 and 1 values are sometimes called "low" and "high," respectively. Binary numbers look strange when they are written out directly. This is because the digits' weight increases by powers of 2, rather than by powers of 10. In a digital numeral, the digit furthest to the right is the "ones" digit; the next digit to the left is the "twos" digit; next comes the "fours" digit, then the "eights" digit, then the "16s" digit, then the "32s" digit, and so on. The decimal equivalent of a binary number can be found by summing all the digits. For example, the binary 10101 is equivalent to the decimal 1 + 4 + 16 = 21 DECIMAL = 21 64 32 16 8 4 2 1 BINARY = 10101 0 0 1 0 1 0 1 Hexadecimal Hexadecimal describes a base-16 number system. That is, it describes a numbering system containing 16 sequential numbers as base units (including 0) before adding a new position for the next number. (Note that we're using "16" here as a decimal number to explain a number that would be "10" in hexadecimal.) The hexadecimal numbers are 0-9 and then use the letters A-F. We show the equivalence of binary, decimal, and hexadecimal numbers in the table below. Hexadecimal is a convenient way to express binary numbers in modern computers in which a byte is almost always defined as containing eight binary digits. When showing the contents of computer storage (for example, when getting a core dump of storage in order to debug a new computer program or when expressing a string of text characters or a string of binary values in coding a program or HT ML page), one hexadecimal digit can represent the arrangement of four binary digits. Two hexadecimal digits can represent eight binary digits, or a byte. Octal Octal (pronounced AHK-tuhl, from Latin octo or "eight") is a term that describes a base-8 number system. An octal number system consists of eight single-digit numbers: 0, 1, 2, 3, 4, 5, 6, and 7. the number after 7 is 10. The number after 17 is 20 and so forth. In computer programming, the octal equivalent of a binary number is sometimes used to represent it because it is shorter. CHARACTERS AND DECIMAL, BINARY, ASCII, EBCDIC VALUE Capital Letters Characters A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Decimal 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 Binary 1000001 1000010 1000011 1000100 1000101 1000110 1000111 1001000 1001001 1001010 1001011 1001100 1001101 1001110 1001111 1010000 1010001 1010010 1010011 1010100 1010101 1010110 1010111 1011000 1011001 1011010 ASCII 1000001 1000010 1000011 1000100 1000101 1000110 1000111 1001000 1001001 1001010 1001011 1001100 1001101 1001110 1001111 1010000 1010001 1010010 1010011 1010100 1010101 1010110 1010111 1011000 1011001 1011010 EBCDIC 01000001 01000010 01000011 01000100 01000101 01000110 01000111 01001000 01001001 01001010 01001011 01001100 01001101 01001110 01001111 01010000 01010001 01010010 01010011 01010100 01010101 01010110 01010111 01011000 01011001 01011010 CHARACTERS AND DECIMAL, BINARY, ASCII, EBCDIC VALUE Small Letters Characters a b c d e f g h i j k l m n o p q r s t u v w x y z Decimal 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 Binary 1100001 1100010 1100011 1100100 1100101 1100110 1100111 1101000 1101001 1101010 1101011 1101100 1101101 1101110 1101111 1110000 1110001 1110010 1110011 1110100 1110101 1110110 1110111 1111000 1111001 1111010 ASCII 1100001 1100010 1100011 1100100 1100101 1100110 1100111 1101000 1101001 1101010 1101011 1101100 1101101 1101110 1101111 1110000 1110001 1110010 1110011 1110100 1110101 1110110 1110111 1111000 1111001 1111010 EBCDIC 01100001 01100010 01100011 01100100 01100101 01100110 01100111 01101000 01101001 01101010 01101011 01101100 01101101 01101110 01101111 01110000 01110001 01110010 01110011 01110100 01110101 01110110 01110111 01111000 01111001 01111010 SHORTCUT KEYS Press ALT+ENTER ALT+Enter ALT+ESC ALT+F4 ALT+SPACEBAR ALT+SPACEBAR ALT+TAB ALT+Underlined letter in a menu name BACKSPACE CTRL while dragging an item CTRL+A CTRL+C CTRL+DOWN ARROW CTRL+ESC CTRL+F4 General keyboard shortcuts To View properties for the selected item. Displays the properties of the selected object. Cycle through items in the order they were opened. Close the active item, or quit the active program. Opens the shortcut menu for the active window. Display the System menu for the active window. Switch between open items. Display the corresponding menu. View the folder one level up in My Computer or Windows Explorer. Copy selected item. Select all. Copy. Move the insertion point to the beginning of the next paragraph. Display the Start menu. Close the active document in programs that allow you to have multiple documents open simultaneously. Move the insertion point to the beginning of the previous word. Move the insertion point to the beginning of the next word. Create shortcut to selected item. Highlight a block of text. Move the insertion point to the beginning of the previous paragraph. Paste. Cut. Undo. Delete. CTRL+LEFT ARROW CTRL+RIGHT ARROW CTRL+SHIFT while dragging an item CTRL+SHIFT with any of the arrow keys CTRL+UP ARROW CTRL+V CTRL+X CTRL+Z DELETE ESC F10 F2 F3 F4 F5 F6 LEFT ARROW RIGHT ARROW SHIFT when you insert a CD into the CD-ROM drive SHIFT with any of the arrow keys SHIFT+DELETE SHIFT+F10 Underlined letter in a command name on an open menu Cancel the current task. Activate the menu bar in the active program. Rename selected item. Search for a file or folder. Display the Address bar list in My Computer or Windows Explorer. Refresh the active window. Cycle through screen elements in a window or on the desktop. Open the next menu to the left, or close a submenu. Open the next menu to the right, or open a submenu. Prevent the CD from automatically playing. Select more than one item in a window or on the desktop, or select text within a document. Delete selected item permanently without placing the item in the Recycle Bin. Display the shortcut menu for the selected item. Carry out the corresponding command. Press Dialog box keyboard shortcuts To Move forward through tabs. Move backward through tabs. Move forward through options. Move backward through options. Carry out the corresponding command or select the corresponding option. Carry out the command for the active option or button. Select or clear the check box if the active option is a check box. Select a button if the active option is a group of option buttons. Display Help. Display the items in the active list. Open a folder one level up if a folder is selected in the Save As or Open dialog box. CTRL+TAB CTRL+SHIFT+TAB TAB SHIFT+TAB ALT+Underlined letter ENTER SPACEBAR Arrow keys F1 F4 BACKSPACE Natural keyboard shortcuts You can use the following keyboard shortcuts with a Microsoft Natural Keyboard or any other compatible keyboard that includes the Windows logo key ( ) and the Application key ( ). Press +BREAK +D +M +Shift+M +E +F CTRL+ +F1 +L +R +U To Display or hide the Start menu. Display the System Properties dialog box. Show the desktop. Minimize all windows. Restores minimized windows. Open My Computer. Search for a file or folder. +F Search for computers. Display Windows Help. Lock your computer if you are connected to a network domain, or switch users if you are not connected to a network domain. Open the Run dialog box. Display the shortcut menu for the selected item. Open Utility Manager. Press Accessibility keyboard shortcuts To Switch Filter Keys on and off. Switch High Contrast on and off. Switch MouseKeys on and off. Switch Sticky Keys on and off. Switch Toggle Keys on and off. Open Utility Manager. Right SHIFT for eight seconds Left ALT +left SHIFT +PRINT SCREEN Left ALT +left SHIFT +NUM LOCK SHIFT five times NUM LOCK for five seconds +U Windows Explorer keyboard shortcuts Press To END HOME NUM LOCK+ASTERISK on numeric keypad (*) NUM LOCK+PLUS SIGN on Display the bottom of the active window. Display the top of the active window. Display all subfolders under the selected folder. Display the contents of the selected numeric keypad (+) NUM LOCK+MINUS SIGN on numeric keypad (-) LEFT ARROW RIGHT ARROW folder. Collapse the selected folder. Collapse current selection if it's expanded or select parent folder. Display current selection if it's collapsed, or select first subfolder. WHAT IS DOS? Microsoft DOS (Disk Operating System) is a command line user interface. MS-DOS 1.0 was released in 1981 for IBM computers and the latest version of MS -DOS is MS-DOS 6.22, which was released in 1994. While MS -DOS is not commonly used by itself today, it still can be accessed from every version of Microsoft Windows by clicking Start / Run and typing "command" or by typing "CMD" in Windows NT, Windows 2000 or Windows XP. Differences between DOS Internal and External Commands Internal commands A command that is stored in the system memory and loaded from the command.com. Below are examples of internal MS -DOS commands currently listed in the Computer dos database. ASSOC CD COLOR DATE DRIVPARM EXIT LOADHIGH MKDIR PAUSE REN SET TYPE BREAK CHDIR COPY DEL ECHO FOR LOCK MOVE PROMPT RENAME SWITCHES CALL CLS CTTY DIR ERASE LH MD PATH RD RMDIR TIME External command A MS-DOS command that is not included in command.com. External commands are commonly external either because it requires large requirements and/or are not commonly used commands. Below are examples of MS-DOS external commands currently listed in the Computer dos database. APPEND AT CHCP CHOICE CONVERT DELTREE DOSKEY EDLIN FASTHELP FIND HELP LOADFIX MORE MSCDEXNT NET NSLOOKUP POWER SCANDISK SHARE SORT TRACERT UNFORMAT ARP ATTRIB CHKDSK COMP DEBUG DISKCOMP DOSSHELL EXPAND FC FORMAT IPCONFIG MEM MSAV MSD NETSTAT PATHPING PRINT SCANREG SHUTDOWN SUBST TREE ASSIGN CACLS CHKNTFS COMPACT DEFRAG DISKCOPY EDIT EXTRACT FDISK GRAFTABL LABEL MODE MSCDEX NBTSTAT NLSFUNC PING ROUTE SETVER SMARTDRV SYS UNDELETE DOS COMMANDS AND EXPLANATION No 01. 02. Command Name ASSOC AT Explanation Displays or modifies file extension associations. Schedules commands and programs to run on a computer. 03. 04. 05. ATTRIB BREAK CACLS Displays or changes file attributes. Sets or clears extended CTRL+C checking. Displays or modifies access control lists (ACLs) of files. 06. 07. CALL CD Calls one batch program from another. Displays the name of or changes the current directory. 08. 09. CHCP CHDIR Displays or sets the active code page number. Displays the name of or changes the current directory. 10. 11. CHKDSK CHKNTFS Checks a disk and displays a status report. Displays or modifies the checking of disk at boot time. 12. 13. CLS CMD Clears the screen. Starts a new instance of the Windows command interpreter. 14. COLOR Sets the default console foreground and background colors. 15. 16. COMP COMPACT Compares the contents of two files or sets of files. Displays or alters the compression of files on NTFS partitions. 17. CONVERT Converts FAT volumes to NTFS. You cannot convert the current drive. 18. 19. 20. 21. COPY DATE DEL DIR Copies one or more files to another location. Displays or sets the date. Deletes one or more files. Displays a list of files and subdirectories in a directory. 22. 23. 24. DISKCOMP DISKCOPY DOSKEY Compares the contents of two floppy disks. Copies the contents of one floppy disk to another. Edits command lines, recalls Windows commands, and creates macros. 25. ECHO Displays messages, or turns command echoing on or off. 26. ENDLOCAL Ends localization of environment changes in a batch file. 27. 28. ERASE EXIT Deletes one or more files. Quits the CMD.EXE program (command interpreter). 29. FC Compares two files or sets of files, and displays the differences between them. 30. 31. 32. FIND FINDSTR FOR Searches for a text string in a file or files. Searches for strings in files. Runs a specified command for each file in a set of files. 33. 34. FORMAT FTYPE Formats a disk for use with Windows. Displays or modifies file types used in file extension associations. 35. GOTO Directs the Windows command interpreter to a labeled line in a batch program. 36. GRAFTABL Enables Windows to display an extended character set in graphics mode. 37. 38. 39. HELP IF LABEL Provides Help information for Windows commands. Performs conditional processing in batch programs. Creates, changes, or deletes the volume label of a disk. 40. 41. 42. 43. 44. MD MKDIR MODE MORE MOVE Creates a directory. Creates a directory. Configures a system device. Displays output one screen at a time. Moves one or more files from one directory to another directory. 45. 46. PATH PAUSE Displays or sets a search path for executable files. Suspends processing of a batch file and displays a message. 47. POPD Restores the previous value of the current directory saved by PUSHD. 48. 49. 50. 51. 52. PRINT PROMPT PUSHD RD RECOVER Prints a text file. Changes the Windows command prompt. Saves the current directory then changes it. Removes a directory. Recovers readable information from a bad or defective disk. 53. REM Records comments (remarks) in batch files or CONFIG.SYS. 54. 55. 56. 57. 58. REN RENAME REPLACE RMDIR SET Renames a file or files. Renames a file or files. Replaces files. Removes a directory. Displays, sets, or removes Windows environment variables. 59. SETLOCAL Begins localization of environment changes in a batch file. 60. SHIFT Shifts the position of replaceable parameters in batch files. 61. 62. SORT START Sorts input. Starts a separate window to run a specified program or command. 63. 64. 65. 66. SUBST TIME TITLE TREE Associates a path with a drive letter. Displays or sets the system time. Sets the window title for a CMD.EXE session. Graphically displays the directory structure of a drive or path. 67. 68. 69. TYPE VER VERIFY Displays the contents of a text file. Displays the Windows version. Tells Windows whether to verify that your files are written correctly to a disk. 70. 71. VOL XCOPY Displays a disk volume label and serial number. Copies files and directory trees. MODEM ERROR MESSAGES No 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 Error Messages An operation is pending. An invalid port handle was detected. The specified port is already open. The caller's buffer is too small. Incorrect information was specified. The port information cannot be set. The specified port is not connected. An invalid event is detected. A device was specified that does not exist. The device type was specified that does not exist. An invalid buffer was specified. A route was specified that is not available. A route was specified that is not allocated. An invalid compression was specified. There were insufficient buffers available. The specified port was not found. An asynchronous request is pending. The modem is already disconnecting. The specified port is not open. The specified port is not connected. No endpoints could be determined. The system could not open the phonebook. The system could not load the phonebook. The system could not find the phonebook entry for this connection. The system could not update the phonebook file. No 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 Error Messages The system found invalid information in the phonebook. A string could not be loaded. A key could not be found. The connection was closed. The connection was closed by the remote computer. The modem was disconnected due to hardware failure. The user disconnected the modem. An incorrect structure size was detected. The modem is already in use or is not configured for dialing out. Your computer could not be registered on the remote network. There was an unknown error. The device attached to the port is not the one expected. A string was detected that could not be converted. The request has timed out. No asynchronous net is available. An error has occurred involving NetBIOS. The server cannot allocate NetBIOS resources needed to support the client. 642 One of your computer's NetBIOS names is already registered on the remote network. 643 644 645 646 647 648 649 650 651 A network adapter at the server failed. You will not receive network message popups. There was an internal authentication error. The account is not permitted to log on at this time of day. The account is disabled. The password for this account has expired. The account does not have permission to dial in. The remote access server is not responding. The modem has reported an error. No 652 653 Error Messages There was an unrecognized response from the modem. A macro required by the modem was not found in the device .INF file section. 654 A command or response in the device .INF file section refers to an undefined macro. 655 656 657 658 659 660 661 662 The <MESSAGE> macro was not found in the device .INF file section. The <DEFAULTOFF> macro in the device .INF file section contains an undefined macro. The device .INF file could not be opened. The device name in the device .INF or media .INI file is too long. The media .INI file refers to an unknown device name. The device .INF file contains no responses for the command. The device .INF file is missing a command. There was an attempt to set a macro not listed in the device .INF file section. 663 664 665 666 667 668 669 670 The media .INI file refers to an unknown device type. The system has run out of memory. The modem is not properly configured. The modem is not functioning. The system was unable to read the media .INI file. The connection was terminated. The usage parameter in the media .INI file is invalid. The system was unable to read the section name from the media .INI file. 671 672 673 674 The system was unable to read the device type from the media .INI file. The system was unable to read the device name from the media .INI file. The system was unable to read the usage from the media .INI file. The system was unable to read the maximum connection BPS rate from the media .INI file. No 675 Error Messages The system was unable to read the maximum carrier connection speed from the media .INI file. 676 677 678 679 680 681 691 The phone line is busy. A person answered instead of a modem. There was no answer. The system could not detect the carrier. There was no dial tone. The modem reported a general error. Access was denied because the user name and/or password was invalid on the domain. 692 695 696 697 699 700 701 There was a hardware failure in the modem. The state machines are not started. The state machines are already started. The response looping did not complete. The modem response caused a buffer overflow. The expanded command in the device .INF file is too long. The modem moved to a connection speed not supported by the COM driver. 703 The connection needs information from you, but the application does not allow user interaction. 704 705 707 708 709 The callback number is invalid. The authorization state is invalid. There was an error related to the X.25 protocol. The account has expired. There was an error changing the password on the domain. The password might have been too short or might have matched a previously used password. 710 Serial overrun errors were detected while communicating with the modem. No 711 Error Messages The Remote Access Service Manager could not start. Additional information is provided in the event log. 712 713 714 715 716 717 The two-way port is initializing. Wait a few seconds and redial. No active ISDN lines are available. No ISDN channels are available to make the call. Too many errors occurred because of poor phone line quality. The remote access service IP configuration is unusable. No IP addresses are available in the static pool of remote access service IP addresses. 718 The connection timed out waiting for a valid response from the remote computer. 719 721 722 The connection was terminated by the remote computer. The remote computer is not responding. Invalid data was received from the remote computer. This data was ignored. 723 726 The phone number, including prefix and suffix, is too long. The IPX protocol cannot be used for dial-out on more than one modem at a time. 728 729 731 732 The system cannot find an IP adapter. SLIP cannot be used unless the IP protocol is installed. The protocol is not configured. Your computer and the remote computer could not agree on PPP control protocols. 733 Your computer and the remote computer could not agree on PPP control protocols. 734 735 736 737 The PPP link control protocol was terminated. The requested address was rejected by the server. The remote computer terminated the control protocol. Loop back detected. No 738 739 Error Messages The server did not assign an address. The authentication protocol required by the remote server cannot use the stored password. Redial, entering the password explicitly. 740 741 742 743 751 An invalid dialing rule was detected. The local computer does not support the required data encryption type. The remote computer does not support the required data encryption type. The remote server requires data encryption. The callback number contains an invalid character. Only the following characters are allowed: 0 to 9, T, P, W, (,), -, @, and space. 752 753 A syntax error was encountered while processing a script. The connection could not be disconnected because it was created by the multi-protocol router. 754 755 The system could not find the multi-link bundle. The system cannot perform automated dial because this entry has a custom dialer specified. 756 757 This connection is already being dialed. Remote access services could not be started automatically. Additional information is provided in the event log. 758 760 761 Internet Connection Sharing is already enabled on the connection. An error occurred while routing capabilities were being enabled. An error occurred while Internet Connection Sharing was being enabled for the connection. 763 Internet Connection Sharing cannot be enabled. There are two or more LAN connections in addition to the connection to be shared. 764 765 No smart card reader is installed. Internet Connection Sharing cannot be enabled. A LAN connection is already configured with the IP address required for automatic IP addressing. No 767 Error Messages Internet Connection Sharing cannot be enabled. The LAN connection selected on the private network has more than one IP address configured. Reconfigure the LAN connection with a single IP address before enabling Internet Connection Sharing. 768 769 770 771 772 The connection attempt failed because of failure to encrypt data. The specified destination is not reachable. The remote machine rejected the connection attempt. The connection attempt failed because the network is busy. The remote computer's network hardware is incompatible with the type of call requested. 773 The connection attempt failed because the destination number has changed. 774 The connection attempt failed because of a temporary failure. Try connecting again. 775 776 The call was blocked by the remote computer. The call could not be connected because the destination has invoked the Do Not Disturb feature. 777 The connection attempt failed because the modem on the remote computer is out of order. 778 780 783 It was not possible to verify the identity of the server. An attempted function is not valid for this connection. Internet Connection Sharing cannot be enabled. The LAN connection selected as the private network is either not present, or is disconnected from the network. Please ensure that the LAN adapter is connected before enabling Internet Connection Sharing. 784 You cannot dial using this connection at logon time, because it is configured to use a user name different than the one on the smart card. If you want to use it at logon time, you must configure it to use the user name on the smart card. No 785 Error Messages You cannot dial using this connection at logon time, because it is not configured to use a smart card. If you want to use it at logon time, you must edit the properties of this connection so that it uses a smart card. 788 The L2TP connection attempt failed because the security layer could not negotiate compatible parameters with the remote computer. 789 The L2TP connection attempt failed because the security layer encountered a processing error during initial negotiations with the remote computer. 791 The L2TP connection attempt failed because security policy for the connection was not found. 792 The L2TP connection attempt failed because security negotiation timed out. 793 The L2TP connection attempt failed because an error occurred while negotiating security. 794 795 796 The Framed Protocol RADIUS attribute for this user is not PPP. The Tunnel Type RADIUS attribute for this user is not correct. The Service Type RADIUS attribute for this user is neither Framed nor Callback Framed. 797 A connection to the remote computer could not be established because the modem was not found or was busy. 799 Internet Connection Sharing (ICS) cannot be enabled due to an IP address conflict on the network. ICS requires the host be configured to use 192.168.0.1. Please ensure that no other client on the network is configured to use 192.168.0.1. 800 Unable to establish the VPN connection. The VPN server may be unreachable, or security parameters may not be configured properly for this connection. ABBREVIATION 01. 02. 03. 04. 05. 06. 07. 08. 09. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. A/L ABC ACE ACK ADC ADSL AI ALGOL ALU ANSI AOL APL ARPANET AS ASCC ASCII ATM ATM BA BASIC BC BCD BCDIC BCO BIS BIT BPS Alphanumeric Atanasoft Berry Computer Automatic Computing Engine Acknowledgement Analog to Digital Converter Asynchronous Digital Subscriber Loop Artificial Intelligence Algorithmic language Arithmetic and Logic Unit American National Standards Institution America On Line A Programming Language Advanced Research Project Auxiliary Storage Automatic Sequence – Controlled Calculator American Standard Cord for Information Interchange Automatic Teller Machines Asynchronous Transfer Mode Binary Address Beginner’s All-Purpose Symbolic Instruction Code Binary Code Binary Coded Decimal Binary Coded Decimal Interchange Code Binary Coded Octal Business Information System Binary Digit Bit Transaction Processing 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. BPS CAD CAE CAI CALS CAM CAM CAR CASE CBASIC CCITT Bits Per Second Computer Aided Design Computer Aided Engineering Computer Aided Instruction Computer Aided Logistic and Support Computer Aided Manufacturing Computer Assisted Manufacture Computer Assisted Retrieval Computer Aided Software Engineering A Complier Vision Of BASIC Consultative Committee For International Telephony And Telegraphy 39. CCTTT Acronym For International Committee or Telephone And Telegraphy 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. CCU CD CDE CDMA CD-ROM CERN CGA CGI CGI CHS CIM CIM CIP CISC CIU CMOS COBOL Central Control Unit Compact Disk Channel Definition Format Common Division Multiple Access Compact Disk-Read Only Memory Center For European Nuclear Research Color Graphic Adaptor Computer Galway Interface Computer Galway Interface Character per Second Computer Input on Microfilm Chief Information Officer Current Instruction Register Complex Instruction Set Computer Computer Interface Unit Complimentary Metal Oxide Semiconductor Common Business Oriented Language 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 69. 70. 71. 72. 73. 74. 75. 76. 77. 78. 79. 80. 81. 82. 83. 84. 85. 86. 87. CODASYL CODEC COL COM CPS CPU CR CRT CSCW CSMACD CU CUI CVT DAC DBA DBMS DDL DDRAM DDRRAM DEC DEM DIMM DML DMP DNS DOI DRAM DSP DTP DVD EAN Conference For Data Systems Language Coder /Decoder Computer Oriented Language Computer Output on Microfilm Character Per Second / Cycles Per Second Control Processing Unit Character Recognition Cathode Ray Tube Computer Supported Co-operative Work Carrier Sense Multiple Access With Collision Detector Control Unit Character User Interface Constraint Voltage Transformer Digital To Analog Converter Data Base Administrator Data Base Management System Data Descript n Language Dynamic Densities Random Access Memory Dynamic Densities Routine Access Memory Digital Equipment Corporation Data Management System Double Inline Memory Module Data manipulation Language Dot Matrix Printer Domain Name Server Dots Pen Inch Dynamic Random Access Memory Digital Signal Processing Desk –Top Publishing Digital Video Interface European Article Number 88. 89. 90. 91. 92. 93. 94. 95. 96. 97. 98. 99. 100. 101. 102. 103. 104. 105. 106. 107. 108. 109. 110. 111. 112. 113. 114. 115. 116. 117. 118. EBCDIC EDI EDSAC EDVAC EFT EGA EL EM EMACS EMAIL ENIAC EOF EOT ERP FAQ FDC FDDI FGL FORTRAN FTP GB GIF GIGO GNU GPC GPIB GPSS GPSS GSM GUS HDML Extended Binary Coder Decimal Interchange Code Electronic Data Interchange Electronic Delay Storage Automatic Calculator Electronic Discrete Vary Able Automatic Computer Electronic Funds Transfer Enhanced Graphics Adaptor Electro Luminescent Electronic Mail Extended Industry Standard Architecture Electronic Mail Electronic Numerical Integrator And Calculator End Of File End Of Transmission Enterprise Requirements Planning Frequently Asked Question Floppy Disk Controller Fiber Distributed Data Interchange Fourth Generation Language Formula Translation File Transfer Protocol Gigabyte Graphical Interchange Format Garbage In Garbage Out Guns Not Unix General Purpose Computer General Purpose Interface Bus General Purpose Systems Simulator Global Positioning System Global System for Mobile Graphical User Interface Hyper Device Markup Language 119. 120. 121. 122. 123. 124. 125. 126. 127. 128. 129. 130. 131. 132. 133. 134. 135. 136. 137. 138. 139. 140. 141. 142. 143. 144. 145. HLL HSP HTML HTTP I/O IBM IBM-PC IC ID IETF IOD IOR IP IP ISA ISDN ISO ISP ISR IU JANET JCL JPEG K KB LAN LASER High Level Language High Speed Printer Hyper Text Markup Language Hyper Text Transfer Protocol Input/Output International Business Machines IBM Personal Computer Integrated Circuits User Identification International Engineering Task Force Input/output Device Instruction Register Information Provider Internet Protocol Industry Standard Architecture Integrated Service Digital Network International Standards Organization Internet Service Provider Information Storage and Retrieval Input Unite Joint Academic Network Joy Control Language Joint Photography Experts Group Kilo Kilo Byte(1024) Local Area Network Light Amplification by the Stimulated Emission of Rendition 146. 147. 148. LCD LCS LDAP Liquid Crystal Display Liquid Crystals Shutter Lightweight Directory Access Protocol 149. 150. 151. 152. 153. 154. 155. 156. 157. 158. 159. 160. 161. 162. 163. 164. 165. 166. 167. 168. 169. 170. 171. 172. 173. 174. 175. 176. 177. 178. 179. LED LIFO LISP LISP LPM LPS LPS LQP LSB LSD LST MAE MAP MAR MB MBR MDAS MF MIDI MIME MIPS MIS ML MODEM MOO MOS MPEG MR MR MSB MSD Light Emitting Diode Last In First Out List Processing Language List Processor Line per Minute Line per Second Line per Minute Letter Quality Printer Least Significant Bit Least Significant Digit Large Scale Integration Metropolitan Area Ethernet Manufacturing Automation Portal Memory Address Register Megabyte Memory Buffer Register Medicate Data Acquisition System Master File Musical Instrument Digital Interface Multipurpose Internet Mailing Extensions Million Instruction Per Second Management Information System Marching Processing Language Modulator Demodulator Mud Object Oriented Metal Oxide Semi Conductors Moving Pictures Experts Group Memory Register Modem Ready Most Significant Bit Most Significant Digit 180. 181. 182. 183. 184. 185. 186. 187. 188. 189. 190. 191. 192. 193. 194. 195. 196. 197. 198. 199. 200. 201. 202. 203. 204. 205. 206. 207. 208. 209. 210. MS-DOS MSI MSN MT NLQ NMF NREN NSFNET NTFS OCR OH OLE OLTP OMF OMR OPCODE OPP OS/2 PBX PC PIO PL POS PPM PPP PROM PSM PSTN RAMAC RD RF Micro Soft Disk Operating System Medium Scale Integration Micro Soft Network Magnetic Tape Near Letter Quality New Master File National Research And Education Network National Science Foundation Network Non Transfer File System Optical Character Reader /Recognition Off Hook Object Linking Embedding Online Transaction Processing Old Master File Optical Mark Recognition Reading Operation Code Object Oriented Programming Operating System/2 Private Branch Exchanges Program Counter (Also Personal Computer) Processor Input/Output Programming Language Point-Of Sale Page Per Minute Point-To Point Protocol Programmable Read Only Memory Personal Identification No Public Switch Telephone Network Random Access Method for Accounting and Control Receive Data Radio-Frequency 211. 212. 213. 214. 215. 216. 217. 218. 219. 220. 221. 222. 223. 224. 225. 226. 227. 228. 229. 230. 231. 232. 233. 234. 235. 236. 237. 238. 239. 240. 241. RGB RISC RJE ROMBIOUS RPG RS-232 SAGE SDRAM SGML SIMM SLIP SLT SNOBOL SOH SRAM S-SEED SSL SVGA TCP TD TELEX TP TRADIC UIS UNIVAC UPC UPS URL USB UT VCD Red Green Blue Reduced Instruction –Set Computer Remote Job Entry Read Only Memory Basic Input Output System Report Program Generator Regular Standard No 232 Semi Automatic Ground Environment Single Dynamic Random Access Memory Standard Generalized Markup Language Single Inline Memory Module Serial Line Internet Protocol Solid Logic Technology String Oriented Symbolic Language Start of Heading Single Random Access Memory Symmetric Self-Electro-Optic-Effect-Devices Secure Sockets Layer Super Video Graphic Adaptor Transmission Control Protocol Transmitted Data Teleprinter Exchange Transaction Processing Transistorized Airborne Digital Computer Universal Information Server Universal Automatic Computer Universal Product Code Uninterrupted Power Supply Uniform Resource Locater Universal Serial Bus User Terminal Visual Display Unit 242. 243. 244. 245. 246. 247. 248. 249. 250. VDU VGA VM VRS VS WAN WORM WP WWW Visual Display Unit Video Graphic Adaptor Virtual Memory Voice Recognize System Virtual Storage Wide-Area Network Write Once Read Many Word Processing World Wide Web