INTRODUCTION TO COMPUTERS

ANIS HASSAN Center of Excellence – Hyderabad

INTRODUCTION TO COMPUTERS

Introduction:

The main purpose of this chapter is:

To introduce the amazing machine, “Computer”, its limitation and characteristics.

To introduce the history of computer. To learn various types of computers in different aspects To know the advantages and impact of computer in our society. To give the first hand knowledge about programming languages and

translator.

Computer: Computer, machine that performs tasks, such as calculations or electronic communication, under the control of a set of instructions called a program. Programs usually reside within the computer and are retrieved and processed by the computer’s electronics. The program results are stored or routed to output devices, such as video display monitors or printers. Computers perform a wide variety of activities reliably, accurately, and quickly.Hardware: What is a computer? A computer is defined as "an electronic device that accepts data (input), performs arithmetic and logical operations using the data (process) to produce information (output). Computers process and store digital signals based on binary arithmetic. Binary arithmetic uses only two digits, 0 and 1, to represent any number, letter or special character. Data--Numbers, characters, images or other method of recording, in a form which can be assessed by a human or (especially) input into a computer, stored and processed there. Information--Data on its own has no meaning, only when interpreted by some kind of data processing system does it take on meaning and become information. For example, the number 1234.56 is data but if it is output as your bank balance then it is information. A set of instructions, called a program, operates the computer. Brief History:The first large-scale electronic digital computer, ENIAC (Electronic Numerical Integrator and Computer), was introduced in 1946. The ENIAC weighed thirty tons, contained 18,000 vacuum tubes, and filled a 30 x 50 foot room, yet was far less powerful than today’s personal computers. In 1955, Bell labs introduce its first transistor computer. Transistors are faster, smaller and create less heat than traditional vacuum tubes, making these computers much more efficient.

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ANIS HASSAN Center of Excellence – Hyderabad

In 1971, the first microprocessor, the Intel 4004, is designed. This single chip contains all the basic parts of a central processor. In 1977, Apple computer Inc., Radio Shack, and Commodore all introduce mass-market computers, beginning the PC era and the microcomputer race. In 1980, IBM hires Paul Allen and Bill Gates to create an operating system for a new PC. IBM allows Allen and Gates to retain the marketing rights to the operating system, called DOS. In 1981, IBM joins the personal computer race with its IBM PC, which runs the new DOS operating system. In 1990, Microsoft releases Windows 3.0, a complete rewrite of previous versions and one in which most desktop users will eventually spend most of their time. Windows 3.0 uses a graphical user interface [GUI]. In 1995, Microsoft releases Windows 95, Microsoft Office 95 and the online Microsoft Network. In 1997, Microsoft releases Microsoft Office 97.Classification of Computers

Mainframe ComputersMinicomputersMicrocomputersSupercomputers

Mainframe computers: are very large, often filling an entire room. They can store enormous of information, can perform many tasks at the same time, can communicate with many users at the same time, and are very expensive. . The price of a mainframe computer frequently runs into the millions of dollars. Mainframe computers usually have many terminals connected to them. These terminals look like small computers but they are only devices used to send and receive information from the actual computer using wires. Terminals can be located in the same room with the mainframe computer, but they can also be in different rooms, buildings, or cities. Large businesses, government agencies, and universities usually use this type of computer.

Minicomputers: are much smaller than mainframe computers and they are also much less expensive. The cost of these computers can vary from a few thousand dollars to several hundred thousand dollars. They possess most of the features found on mainframe computers, but on a more limited scale. They can still have many terminals, but not as many as the mainframes. They can store a tremendous amount of information, but again usually not as much as the mainframe. Medium and small businesses typically use these computers.

Microcomputers: are the types of computers we are using in your classes at Floyd College. These computers are usually divided into desktop models and laptop models. They are terribly limited in what they can do when compared to the larger models discussed above because they can only be used by one person at a time, they are much slower than the larger computers, and they cannot store nearly as much information, but they are excellent when used in small businesses, homes, and school classrooms. These computers are inexpensive and easy to use. They have become an indispensable part of modern life.

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Computer TasksInputStorageProcessingOutput

When a computer is asked to do a job, it handles the task in a very special way. It accepts the information from the user. This is called input.It stored the information until it is ready for use. The computer has memory chips, which are designed to hold information until it is needed.It processes the information. The computer has an electronic brain called the Central Processing Unit, which is responsible for processing all data and instructions given to the computer.It then returns the processed information to the user. This is called output.

Every computer has special parts to do each of the jobs listed above. Whether it is a multimillion dollar mainframe or a thousand dollar personal computer, it has the following four components, Input, Memory, Central Processing, and Output.

The central processing unit is made up of many components, but two of them are worth mentioning at this point. These are the arithmetic and logic unit and the control unit. The control unit controls the electronic flow of information around the computer. The arithmetic and logic unit, ALU, is responsible for mathematical calculations and logical comparisons.

Input DevicesKeyboardMouseScannerMicrophoneCD-ROMJoystick

Output Devices

MonitorSpeakersPrinter

ImpactDaisy WheelDot Matrix

Non-ImpactInk Jet Laser

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Storage DevicesFloppy diskTape driveLocal drive (c)Network drive (z)CD-ROMZip disk

MemoryRead Only Memory (ROM)

ROM is a small area of permanent memory that provides startup instructions when the computer is turned on. You can not store any data in ROM. The instructions in ROM are set by the manufacturer and cannot be changed by the user. The last instruction in ROM directs the computer to load the operating system.

Every computer needs an operating system. This is a special computer program that must be loaded into memory as soon as the computer is turned on. Its purpose is to translate your instructions in English into Binary so that the computer can understand your instructions. The operating system also translates the results generated by your computer into English when it is finished so that we can understand and use the results. The operating system comes with a computer.

Random Access Memory (RAM)

This is the area of memory where data and program instructions are stored while the computer is in operation. This is temporary memory. NOTE: The data stored in RAM is lost forever when the power is turned off. For this reason it is very important that you save your work before turning off your computer. This is why we have peripheral storage devices like your computer’s hard disk and floppy diskettes. Permanent Memory (Auxiliary Storage)Your files are stored in permanent memory only when saved to your disk in a: drive or saved to your computer's hard disk, Drive c:

To better understand how a computer handles information and to also understand why information is lost if the power goes off, let’s take a closer look at how a computer handles information. Your computer is made of millions of tiny electric circuits. For every circuit in a computer chip, there are two possibilities:

an electric circuit flows through the circuit orAn electric circuit does not flow through the circuit.

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When an electric current flows through a circuit, the circuit is on. When no electricity flows, the circuit is off. An “on” circuit is represented by the number one (1) and an off circuit is represented by the number zero (0). The two numbers 1 and 0 are called bits. The word bit comes from “binary digit”. Each time a computer reads an instruction, it translates that instruction into a series of bits, 1’s and 0’s. On most computers every character from the keyboard is translated into eight bits, a combination of eight 1’s and 0’s. Each group of eight bits is called a byte.

Byte – The amount of space in memory or on a disk needed to store one character. 8 bits = 1 Byte

Since computers can handle such large numbers of characters at one time, metric prefixes are combined with the word byte to give some common multiples you will encounter in computer literature.

Kilo means 1000 kilobyte (KB) = 1000 BytesMega means 1,000,000 megabyte (MB) = 1,000,000 BytesGiga Means 1,000,000,000 gigabyte (GB) = 1,000,000,000 Bytes

As a side note, the laptop computers that you are using at Floyd College have 32 MB of RAM.

At this point it would be good to point out why information stored in RAM is lost if the power goes off. Consider the way the following characters are translated into binary code for use by the computer.

A 01000001B 01000010C 01000011X 01011000Z 01011010

0011000100110010

Consider the column at the right, which represents how the computer stores information. Each of the 1’s in the second column represents a circuit that is “on”. If the power goes off, these circuits can NOT be “on” any more because the electricity has been turned off and any data represented by these circuits is lost. ABACUS

Fascinating facts about the invention of the Abacus by Chinese in 3000 BC.Calculation was a need from the early days when it was necessary to account to others for individual or group actions, particularly in relation to maintaining inventories (of flocks of sheep) or reconciling finances. Early man counted by means of matching one set of objects with another set (stones and sheep).

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The operations of addition and subtraction were simply the operations of adding or subtracting groups of objects to the sack of counting stones or pebbles. Early counting tables, named abaci, not only formalized this counting method but also introduced the concept of positional notation that we use today.

The next logical step was to produce the first "personal calculator"—the abacus—which used the same concepts of one set of objects standing in for objects in another set, but also the concept of a single object standing for a collection of objects—positional notation. The Chinese abacus was developed about 5000 years ago. It was built out of wood and beads. It could be held and carried around easily. The abacus was so successful that its use spread form China to many other countries. The abacus is still in use in some countries today. The abacus does not actually do the computing, as today's calculators do. It helps people keep track of numbers as they do the computing. People who are good at using an abacus can often do calculations as quickly as a person who is using a calculatorThis one-for-one correspondence continued for many centuries even up through the many years when early calculators used the placement of holes in a dial to signify a count—such as in a rotary dial telephone. Although these machine often had the number symbol engraved alongside the dial holes, the user did not have to know the relationship between the symbols and their numeric value.Primitive people also needed a way to calculate and store information for future use. To keep track of the number of animals killed, they collected small rocks and pebbles in a pile. Each stone stood for one animal. Later they scratched notches and symbols in stone or wood to record and store information. Only when the process of counting and arithmetic became a more abstract process and different sizes of groups were given a symbolic representation so that the results could be written on a "storage medium" such as papyrus or clay did the process of calculation become a process of symbol manipulation.

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ANIS HASSAN Center of Excellence – Hyderabad

AT A GLANCE:

Invention: abacus in c3000 BCab·a·cus  / noun .

Function: A counting device: a mechanical device for making calculations consisting of a frame mounted with rods along which beads or balls are moved

Nationality:

Chinese

The First Computer

IntroductionSeldom, if ever, in the history of technology has so long an interval separated the invention of a device and its realization in hardware as that which elapsed between Charles Babbage's description, in 1837, of the Analytical Engine, a mechanical digital computer which, viewed with the benefit of a century and a half's hindsight, anticipated virtually every aspect of present-day computers. Charles Babbage (1792-1871) was an eminent figure in his day, elected Lucasian Professor of Mathematics at Cambridge in 1828 (the same Chair held by Newton and, in our days, Stephen Hawking); he resigned this professorship in 1839 to devote his full attention to the Analytical Engine. Babbage was a Fellow of the Royal Society and co-founder of the British Association for the Advancement of Science, the Royal Astronomical Society, and the Statistical Society of London. He was a close acquaintance of Charles Darwin, Sir John Herschel, Laplace, and Alexander Humboldt, and was author of more than eighty papers and books on a broad variety of topics. His vision of a massive brass, steam-powered, general-purpose, mechanical computer inspired some of the great minds of the nineteenth century but failed to persuade any backer to provide the funds to actually construct it. It was only after the first electromechanical and later, electronic computers had been built in the twentieth century, that designers of those machines discovered the extent to which Babbage had anticipated almost every aspect of their work. These pages are an on-line museum celebrating Babbage's Analytical Engine. Here you will find a collection of original historical documents tracing the evolution of the Engine from the original concept through concrete design, ending in disappointment when it became clear it would never be built. You'll see concepts used every day in the design and programming of modern computers described for the very first time, often in a manner more lucid than contemporary expositions. You'll get a sense of how mathematics, science, and technology felt in the nineteenth century, and for the elegant language used in discussing those disciplines, and thereby peek into the personalities

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of the first computer engineer and programmer our species managed to produce. If you are their intellectual heir, perhaps you'll see yourself and your own work through their Victorian eyes. Since we're fortunate enough to live in a world where Babbage's dream has been belatedly realized, albeit in silicon rather than brass, we can not only read about The Analytical Engine but experience it for ourselves. These pages include a Java-based emulator for The Analytical Engine and a variety of programs for it. You can run the emulator as an applet within a Web page or as a command-line application on your own computer (assuming it is equipped with a Java runtime environment). These pages are a museum, and its lobby is the Table of Contents, to which all other documents are linked. Rather than forcing you to follow a linear path through the various resources here, you can explore in any order you wish, returning to the Table of Contents to select the next document that strikes you as interesting. Every page has a link to the Table of Contents at the bottom, so it's easy to get back when you've finished reading a document or decided to put it aside and explore elsewhere.

The Five Generations of ComputersThe 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, 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.

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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. Second-generation 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 CircuitsThe 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: MicroprocessorsThe 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 IntelligenceFifth 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 Software

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System Software System software will come provided with each computer and is necessary for the computer’s operation. This software acts as an interpreter between the computer and user. It interprets your instructions into binary code and likewise interprets binary code into language the user can understand. In the past you may have used MS-DOS or Microsoft Disk Operating System which was a command line interface. This form of system software required specific commands to be typed. Windows 95 is a more recent version of system software and is known as a graphical interface. This means that it uses graphics or "icons" to represent various operations. You no longer have to memorize commands; you simply point to an icon and click.

Program Software Program software is software used to write computer programs in specific computer languages.

Application Software Application software is any software used for specified applications such as:

Word ProcessingSpreadsheetDatabasePresentation GraphicsCommunication Tutorials Entertainment, Games

THE INTERNET

The Internet is a global computer and resource network that provides the user with a huge amount of information and services including such things as database access, electronic mail (E-Mail), file transport, discussion lists, on-line news, weather information, bulletin boards, airline traffic, crop production, on-line text books, and services offered by the World Wide Web, Gopher and WAIS. Now, what does all of this mean to the practicing physician? The main advantage of the Internet is the interactive exchange of information regardless of location or medium. Researchers and commercial and federal agencies were looking for methods to interconnect computers and various attached devices to allow for this exchange and sharing of information. Physically linking computers and other devices together with cables, telephone lines, satellite links, and special electronic equipment into a computer network has been accomplished, but at a cost: proprietary and often complex, incompatible and expensive systems resulted. Interconnectivity of individual networks and different technologies to form larger networks that could span the world became prudent. Nowadays, the term "Information Superhighway" is being used to illustrate that need, but that term is more a political smoke screen than a truthful representation of the Internet. The

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Internet (Note the capital I) is NOT a "network of networks." There is no such thing. Nor is the Internet maintained or managed by someone or some organization. These fallacies do injustice to the Internet since they only address the physical layer and do not emphasize the functional integration of the diverse and dispersed resources that this physical layer transports. To appreciate the current state of the Internet, it is helpful to spend some time on its roots. Interestingly, the United States Department of Defense early on recognized and funded research in the area of interconnecting diverse networks. Toward this goal, the Advanced Research Projects Agency (ARPA) of the United States in the mid-1960's sponsored universities and other research organizations in developing a protocol that would satisfy ARPA's (military) requirements: being able to withstand a nuclear attack. In the late 1960's, the Internet Protocol and Transmission Control Protocol (TCP/IP) family of protocols was completed. The TCP/IP protocol that resulted is the basis of the current Internet user community and defines how computers do such things as start an interconnection, send data back and forth, or terminate a connection. The initial "Internet" was primarily a private information access tool for researchers and scientists at universities and federal agencies. However, the ease of interconnecting TCP/IP networks together, combined with the fact that TCP/IP networks are allowed to grow without disrupting existing networks, and the policy to make the TCP/IP protocol available to everyone in both the academic and research environment has stimulated today's enormous popularity. Soon, networks based on the TCP/IP protocol grew from just a few hundred computers to the world largest network of academic, government, commercial, and educational networks interconnecting millions of systems. Who Pays for the Internet?The federal government through the National Science Foundation subsidizes the Internet. Academic institutions and commercial parties also bear some of the cost to make an Internet connection available to their faculty, students, and employees. Nowadays, Internet connections for home use are becoming available from commercial providers. It should not come as a surprise in the current climate of cost containment that the federal subsidies are being reduced, if not phased out, and that private industry replaces this financial void such as CompuServe and America Online. The other side of the coin is that commercialization will increase on the Internet. How does it Work?

When we pick up the phone to make a call, a dedicated connection between our phone and the other phone is made. This type of dedicated connection is called circuit-switched. All

communication between the two stations uses the established dedicated connection. Network connections rely on another type of connection: packet-switched. Compared to circuit-switched, there is no dedicated connection between the two systems. The information stream is chopped into small pieces (packets) that are placed onto the network by the network hardware of the source system. It is the responsibility of other network hardware to deliver

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that packet to the destination using the address of the destination system that is contained in each packet. Once the destination receives the packets, they must be re-assembled into the original information stream. The network hardware only knows where to deliver the packet and need not know what the route is the packet will be traveling. How then does the network know where to send the packet? The answer to this question is: every computer system that is on the Internet has a unique address referred to as the Internet address or IP number. (Please note that this is NOT your E-Mail address.) This unique address is a 32-bit number, but to make it more readable for us humans it is commonly written as four numbers separated by periods also called the dotted decimal notation. Internet address written in the dotted decimal notation When you want to connect your computer to the Internet you must obtain such a unique address. If you wish to communicate with another computer over the Internet, you need to know the other system's IP number. We humans are better at remembering names rather than numbers and, therefore, each computer on the Internet can also be given a name. However, since the computer really uses the IP number, the corresponding IP address needs to be found for each name, similar to the way we use a telephone book. The TCP/IP family of protocols defines the standard of how to communicate among the interconnected networks of the Internet. This set of rules allows systems from various manufacturers, running different computer software on incompatible hardware to exchange information, provide the TCP/IP standards were followed. These standards define how the packets look, how computers set up a connection to exchange data, what to do in case of errors, and so on. The versatility of the TCP/IP protocol was illustrated in 1978 when a dumb terminal located in a mobile van driving along a California highway made a connection to a computer located in London, England. Modern computer networks are comprised of powerful personal computers instead of dumb terminals, but the basic TCP/IP services: file transfer (the File Transport Protocol FTP), remote access to a host computer (Telnet), and electronic mail (E-MAIL), are very much an essential part of any TCP/IP implementation.The History of Computer Programming Languages

           Ever since the invention of Charles Babbage's difference engine in 1822, computers have required a means of instructing them to perform a specific task. This means is known as a programming language. Computer languages were first composed of a series of steps to wire a particular program; these morphed into a series of steps keyed into the computer and then executed; later these languages acquired advanced features such as logical branching and object orientation. The computer languages of the last fifty years have come in two stages, the first major languages and the second major languages, which are in use today.           In the beginning, Charles Babbage's difference engine could only be made to execute tasks by changing the gears which executed the calculations. Thus, the earliest form of a computer language was physical motion. Eventually, physical motion was replaced by electrical signals when the US Government built the ENIAC in 1942. It followed many of the same

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principles of Babbage's engine and hence, could only be "programmed" by presetting switches and rewiring the entire system for each new "program" or calculation. This process proved to be very tedious.    In 1945, John Von Neumann was working at the Institute for Advanced Study. He developed two important concepts that directly affected the path of computer programming languages. The first was known as "shared-program technique" (www.softlord.com). This technique stated that the actual computer hardware should be simple and not need to be hand-wired for each program. Instead, complex instructions should be used to control the simple hardware, allowing it to be reprogrammed much faster.

           The second concept was also extremely important to the development of programming languages. Von Neumann called it "conditional control transfer" (www.softlord.com). This idea gave rise to the notion of subroutines, or small blocks of code that could be jumped to in any order, instead of a single set of chronologically ordered steps for the computer to take. The second part of the idea stated that computer code should be able to branch based on logical statements such as IF (expression) THEN, and looped such as with a FOR statement. "Conditional control transfer" gave rise to the idea of "libraries," which are blocks of code that can be reused over and over.

           In 1949, a few years after Von Neumann's work, the language Short Code appeared (www.byte.com). It was the first computer language for electronic devices and it required the programmer to change its statements into 0's and 1's by hand. Still, it was the first step towards the complex languages of today. In 1951, Grace Hopper wrote the first compiler, A-0 (www.byte.com). A compiler is a program that turns the language's statements into 0's and 1's for the computer to understand. This lead to faster programming, as the programmer no longer had to do the work by hand.

           In 1957, the first of the major languages appeared in the form of FORTRAN. Its name stands for FORmula TRANslating system. The language was designed at IBM for scientific computing. The components were very simple, and provided the programmer with low-level access to the computers innards. Today, this language would be considered restrictive as it only included IF, DO, and GOTO statements, but at the time, these commands were a big step forward. The basic types of data in use today got their start in FORTRAN, these included logical variables (TRUE or FALSE), and integer, real, and double-precision numbers.

           Though FORTAN was good at handling numbers, it was not so good at handling input and output, which mattered most to business computing. Business computing started to take off in 1959, and because of this, COBOL was developed. It was designed from the ground up as the language for businessmen. Its only data types were numbers and strings of text. It also allowed for these to be grouped into arrays and records, so that data could be tracked and organized better. It is interesting to note that a COBOL program is built in a way similar to an essay, with four or five major sections that build

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into an elegant whole. COBOL statements also have a very English-like grammar, making it quite easy to learn. All of these features were designed to make it easier for the average business to learn and adopt it.

           In 1958, John McCarthy of MIT created the LISt Processing (or LISP) language. It was designed for Artificial Intelligence (AI) research. Because it was designed for such a highly specialized field, its syntax has rarely been seen before or since. The most obvious difference between this language and other languages is that the basic and only type of data is the list, denoted by a sequence of items enclosed by parentheses. LISP programs themselves are written as a set of lists, so that LISP has the unique ability to modify itself, and hence grow on its own. The LISP syntax was known as "Cambridge Polish," as it was very different from standard Boolean logic (Wexelblat, 177) :x V y - Cambridge Polish, what was used to describe the LISP programOR(x,y) - parenthesized prefix notation, what was used in the LISP programx OR y - standard Boolean logic

LISP remains in use today because its highly specialized and abstract nature.

           The Algol language was created by a committee for scientific use in 1958. Its major contribution is being the root of the tree that has led to such languages as Pascal, C, C++, and Java. It was also the first language with a formal grammar, known as Backus-Naar Form or BNF (McGraw-Hill Encyclopedia of Science and Technology, 454). Though Algol implemented some novel concepts, such as recursive calling of functions, the next version of the language, Algol 68, became bloated and difficult to use (www.byte.com). This lead to the adoption of smaller and more compact languages,such as Pascal.           Pascal was begun in 1968 by Niklaus Wirth. Its development was mainly out of necessity for a good teaching tool. In the beginning, the language designers had no hopes for it to enjoy widespread adoption. Instead, they concentrated on developing good tools for teaching such as a debugger and editing system and support for common early microprocessor machines which were in use in teaching institutions.

           Pascal was designed in a very orderly approach, it combined many of the best features of the languages in use at the time, COBOL, FORTRAN, and ALGOL. While doing so, many of the irregularities and oddball statements of these languages were cleaned up, which helped it gain users (Bergin, 100-101). The combination of features, input/output and solid mathematical features, made it a highly successful language. Pascal also improved the "pointer" data type, a very powerful feature of any language that implements it. It also added a CASE statement that allowed instructions to to branch like a tree in such a manner:

Programming Languages

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All computers have an internal machine language which they execute directly. This language is coded in a binary representation and is very tedious to write. Most instructions will consist of an operation code part and an address part. The operation code indicates which operation is to be carried out while the address part of the instruction indicates which memory location is to be used as the operand of the instruction. For example in a hypothetical computer successive bytes of a program may contain:

operation code

address meaning

00010101 10100001 load c(129) into accumulator00010111 10100010 add c(130) to accumulator00010110 10100011 store c(accumulator) in location 131

where c( ) means `the contents of' and the accumulator is a special register in the CPU. This sequence of code then adds the contents of location 130 to the contents of the accumulator, which has been previously loaded with the contents of location 129, and then stores the result in location 131. Most computers have no way of deciding whether a particular bit pattern is supposed to represent data or an instruction. Programmers using machine language have to keep careful track of which locations they are using to store data, and which locations are to form the executable program. Programming errors which lead to instructions being overwritten with data, or erroneous programs which try to execute part of their data are very difficult to correct. However the ability to interpret the same bit pattern as both an instruction and as data is a very powerful feature; it allows programs to generate other programs and have them executed. Assembly Language The bookkeeping involved in machine language programming is very tedious. If a programmer is modifying a program and decides to insert an extra data item, the addresses of other data items may be changed. The programmer will have to carefully examine the whole program deciding which bit patterns represent the addresses which have changed, and modify them. Human beings are notoriously bad at simple repetitive tasks; computers thrive on them. Assembly languages are a more human friendly form of machine language. Machine language commands are replaced by mnemonic commands on a one-to-one basis. The assembler program takes care of converting from the mnemonic to the corresponding machine language code. The programmer can also use symbolic addresses for data items. The assembler will assign machine addresses and ensure that distinct data items do not overlap in storage, a depressingly common occurrence in machine language programs. For example the short section of program above might be written in assembly language as:

operation address

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codeLOAD AADD BSTORE C

Obviously this leaves less scope for error but since the computer does not directly understand assembly language this has to be translated into machine language by a program called an assembler. The assembler replaces the mnemonic operation codes such as ADD with the corresponding binary codes and allocates memory addresses for all the symbolic variables the programmer uses. It is responsible for associating the symbol A, B, and C with an addresses, and ensuring that they are all distinct. Thus by making the process of programming easier for the human being another level of processing for the computer has been introduced. Assembly languages are still used in some time-critical programs since they give the programmer very precise control of what exactly happens inside the computer. Assembly languages still require that the programmer should have a good knowledge of the internal structure of the computer. For example, different ADD instructions will be needed for different types of data item. Assembly languages are still machine specific and hence the program will have to be re-written if it is to be implemented on another type of computer.

High level Languages Very early in the development of computers attempts were made to make programming easier by reducing the amount of knowledge of the internal workings of the computer that was needed to write programs. If programs could be presented in a language that was more familiar to the person solving the problem, then fewer mistakes would be made. High-level programming languages allow the specification of a problem solution in terms closer to those used by human beings. These languages were designed to make programming far easier, less error-prone and to remove the programmer from having to know the details of the internal structure of a particular computer. These high-level languages were much closer to human language. One of the first of these languages was Fortran II which was introduced in about 1958. In Fortran II our program above would be written as:C = A + Bwhich is obviously much more readable, quicker to write and less error-prone. As with assembly languages the computer does not understand these high-level languages directly and hence they have to be processed by passing them through a program called a compiler which translates them into internal machine language before they can be executed. Another advantage accrues from the use of high-level languages if the languages are standardized by some international body. Then each manufacturer produces a compiler to compile programs that conform to the standard into their own internal machine language. Then it should be easy to

MAJID AZIZ KALERI

ANIS HASSAN Center of Excellence – Hyderabad

take a program which conforms to the standard and implement it on many different computers merely by re-compiling it on the appropriate computer. This great advantage of portability of programs has been achieved for several high-level languages and it is now possible to move programs from one computer to another without too much difficulty. Unfortunately many compiler writers add new features of their own which means that if a programmer uses these features then their program becomes non-portable. It is well worth becoming familiar with the standard and writing programs which obey it, so that your programs are more likely to be portable. As with assembly language human time is saved at the expense of the compilation, time required to translate the program to internal machine language. The compilation time used in the computer is trivial compared with the human time saved, typically seconds as compared with weeks. Many high level languages have appeared since Fortran II (and many have also disappeared!), among the most widely used have been: COBOL Business applicationsFORTRAN Engineering & Scientific ApplicationsPASCAL General use and as a teaching toolC & C++ General Purpose - currently most popularPROLOG Artificial IntelligenceJAVA General Purpose - gaining popularity rapidlyAll these languages are available on a large variety of computers.

Central Processing Unit The Central Processing Unit (CPU) performs the actual processing of data. The data it processes is obtained, via the system bus, from the main memory. Results from the CPU are then sent back to main memory via the system bus. In addition to computation the CPU controls and co-ordinates the operation of the other major components. The CPU has two main components, namely: The Control Unit -- controls the fetching of instructions from the main memory and the subsequent execution of these instructions. Among other tasks carried out are the control of input and output devices and the passing of data to the Arithmetic/Logical Unit for computation.The Arithmetic/Logical Unit (ALU) -- carries out arithmetic operations on integer (whole number) and real (with a decimal point) operands. It can also perform simple logical tests for equality and greater than and less than between operands.It is worth noting here that the only operations that the CPU can carry out are simple arithmetic operations, comparisons between the result of a calculation and other values, and the selection of the next instruction for processing. All the rest of the apparently limitless things a computer can do are built on this very primitive base by programming! Modern CPUs are very fast. At the time of writing, the CPU of a typical PC is capable of executing many tens of millions of instructions per second.

MAJID AZIZ KALERI

ANIS HASSAN Center of Excellence – Hyderabad

Computer busIn computer architecture, a bus is a subsystem that transfers data or power between computer components inside a computer or between computers. Unlike a point-to-point connection, a bus can logically connect several peripherals over the same set of wires. Each bus defines its set of connectors to physically plug devices, cards or cables together.Early computer buses were literally parallel electrical buses with multiple connections, but the term is now used for any physical arrangement that provides the same logical functionality as a parallel electrical bus. Modern computer buses can use both parallel and bit-serial connections, and can be wired in either a multidrop (electrical parallel) or daisy chain topology, or connected by switched hubs, as in the case of USB.

Memory The memory of a computer can hold program instructions, data values, and the intermediate results of calculations. All the information in memory is encoded in fixed size cells called bytes. A byte can hold a small amount of information, such as a single character or a numeric value between 0 and 255. The CPU will perform its operations on groups of one, two, four, or eight bytes, depending on the interpretation being placed on the data, and the operations required. There are two main categories of memory, characterised by the time it takes to access the information stored there, the number of bytes which are accessed by a single operation, and the total number of bytes which can be stored. Main Memory is the working memory of the CPU, with fast access and limited numbers of bytes being transferred. External memory is for the long term storage of information. Data from external memory will be transferred to the main memory before the CPU can operate on it. Access to the external memory is much slower, and usually involves groups of several hundred bytes.

Main memory The main memory of the computer is also known as RAM, standing for Random Access Memory. It is constructed from integrated circuits and needs to have electrical power in order to maintain its information. When power is lost, the information is lost too! It can be directly accessed by the CPU. The access time to read or write any particular byte are independent of whereabouts in the memory that byte is, and currently is approximately 50 nanoseconds (a thousand millionth of a second). This is broadly comparable with the speed at which the CPU will need to access data. Main memory is expensive compared to external memory so it has limited capacity. The capacity available for a given price is increasing all the time. For example many home Personal Computers now have a capacity of 16 megabytes (million bytes), while 64 megabytes is commonplace on commercial workstations. The CPU will normally transfer data to and from the main memory in groups of two, four or eight bytes, even if the operation it is undertaking only requires a single byte. External Memory

MAJID AZIZ KALERI

ANIS HASSAN Center of Excellence – Hyderabad

External memory which is sometimes called backing store or secondary memory, allows the permanent storage of large quantities of data. Some method of magnetic recording on magnetic disks or tapes is most commonly used. More recently optical methods which rely upon marks etched by a laser beam on the surface of a disc (CD-ROM) have become popular, although they remain more expensive than magnetic media. The capacity of external memory is high, usually measured in hundreds of megabytes or even in gigabytes (thousand million bytes) at present. External memory has the important property that the information stored is not lost when the computer is switched off. The most common form of external memory is a hard disc which is permanently installed in the computer and will typically have a capacity of hundreds of megabytes. A hard disc is a flat, circular oxide-coated disc which rotates continuously. Information is recorded on the disc by magnetising spots of the oxide coating on concentric circular tracks. An access arm in the disc drive positions a read/write head over the appropriate track to read and write data from and to the track. This means that before accessing or modifying data the read/write head must be positioned over the correct track. This time is called the seek time and is measured in milliseconds. There is also a small delay waiting for the appropriate section of the track to rotate under the head. This latency is much smaller than the seek time. Once the correct section of the track is under the head, successive bytes of information can be transferred to the main memory at rates of several megabytes per second. This discrepancy between the speed of access to the first byte required, and subsequent bytes on the same track means that it is not economic to transfer small numbers of bytes. Transfers are usually of blocks of several hundred bytes or even more. Notice that the access time to data stored in secondary storage will depend on its location. The hard disc will hold all the software that is required to run the computer, from the operating system to packages like word-processing and spreadsheet programs. All the user's data and programs will also be stored on the hard disc. In addition most computers have some form of removable storage device which can be used to save copies of important files etc. The most common device for this purpose is a floppy disc which has a very limited capacity. Various magnetic tape devices can be used for storing larger quantities of data and more recently removable optical discs have been used. It is important to note that the CPU can only directly access data that is in main memory. To process data that resides in external memory the CPU must first transfer it to main memory. Accessing external memory to find the appropriate data is slow (milliseconds) in relation to CPU speeds but the rate of transfer of data to main memory is reasonably fast once it has been located.

MAJID AZIZ KALERI

ANIS HASSAN Center of Excellence – Hyderabad

Input/Output Devices When using a computer the text of programs, commands to the computer and data for processing have to be entered. Also information has to be returned from the computer to the user. This interaction requires the use of input and output devices. The most common input devices used by the computer are the keyboard and the mouse. The keyboard allows the entry of textual information while the mouse allows the selection of a point on the screen by moving a screen cursor to the point and pressing a mouse button. Using the mouse in this way allows the selection from menus on the screen etc. and is the basic method of communicating with many current computing systems. Alternative devices to the mouse are tracker balls, light pens and touch sensitive screens. The most common output device is a monitor which is usually a Cathode Ray Tube device which can display text and graphics. If hard-copy output is required then some form of printer is used. PortIn computing, a port (derived from seaport) is usually a connection through which data is sent and received. An exception is a software port (porting, derived from transport), which is software that has been "transported" to another computer systemSerial port

A male DE-9 serial port on the rear panel of a PC.In computing, a serial port is an interface on a computer system with which information is transferred in or out one bit at a time (contrast parallel port). Throughout most of the history of personal computers, this was accomplished using the RS-232 standard over simple cables connecting the computer to a device such as a terminal or modem. Mice, keyboards, and other devices were also often connected this way.Parallel portIn computing, a parallel port is an interface from a computer system where data is transferred in or out in parallel, that is, on more than one wire. A parallel port carries one bit on each wire thus multiplying the transfer rate obtainable over a single cable (contrast serial port). There are also several extra wires on the port that are used for control and status signals to indicate when data is ready to be sent or received, initiate a reset, indicate an error condition (such as paper out), and so forth. On many modern (2005) computers, the parallel port is omitted for cost savings, and is considered to be a legacy port

MAJID AZIZ KALERI