Computer Fundamentals PDF

1 INTRODUCTION TO COMPUTER Contents  Digital and analog computers  Characteristics of computer—Speed, accuracy, diligence, storage capability, versatility  History of computer—Calculating machines, Napier’s bones, slide rule, Pascal's adding and subtraction machine, Lei...

1 INTRODUCTION TO COMPUTER Contents  Digital and analog computers  Characteristics of computer—Speed, accuracy, diligence, storage capability, versatility  History of computer—Calculating machines, Napier’s bones, slide rule, Pascal's adding and subtraction machine, Leibniz's multiplication and dividing machine, punch card system, Babbage's analytical engine, Hollerith's punched card tabulating machine  Generations of computer o First generation (1940 to 1956): Using vacuum tubes o Second generation (1956 to 1963): Using transistors o Third generation (1964 to 1971): Using integrated circuits o Fourth generation (1971 to present): Using microprocessors o Fifth generation (present and next): Using artificial intelligence  Classification of computer—Microcomputers (desktop computer or Personal Computer (PC), notebook computers or laptop, netbook, tablet computer, handheld computer or Personal Digital Assistant (PDA), smart phones), minicomputers, mainframe computers, supercomputers )  The computer system—Hardware, software, data, users  The Input-process-output concept  Components of computer hardware—Input/output unit, central processing unit, storage unit  Application of computers—Education, entertainment, sports, advertising, medicine, science and engineering, government, home Why this chapter Computers are an integral part of our lives. Wherever we are—sitting in our homes, working in the office, driving on roads, sitting in a movie hall, staying in a hotel, etc.—our lives are directly or indirectly affected by the computers. In this era of information, we are dependent on the storage, flow and processing of data and information, which can only be possible with the help of computers. The purpose of this chapter is to introduce you to the “computer”. 1.1 INTRODUCTION Nowadays, computers are an integral part of our lives. They are used for the reservation of tickets for airplanes and railways, payment of telephone and electricity bills, deposit and withdrawal of money from banks, processing of business data, forecasting of weather conditions, diagnosis of diseases, searching for information on the Internet, etc. Computers are also used extensively in schools, universities, organizations, music industry, movie industry, scientific research, law firms, fashion industry, etc. The term computer is derived from the word compute. The word compute means to calculate. A computer is an electronic machine that accepts data from the user, processes the data by performing calculations and operations on it, and generates the desired output results. Computer performs both simple and complex operations, with speed and accuracy. This chapter discusses the history and evolution of computer, the concept of input-process-output and the characteristics of computer. This chapter also discusses the classification of digital computers based on their size and type, and the application of computer in different domain areas. 1.2 DIGITAL AND ANALOG COMPUTERS A digital computer uses distinct values to represent the data internally. All information are represented using the digits Os and 1s. The computers that we use at our homes and offices are digital computers. Analog computer is another kind of a computer that represents data as variable across a continuous range of values. The earliest computers were analog computers. Analog computers are used for measuring of parameters that vary continuously in real time, such as temperature, pressure and voltage. Analog computers may be more flexible but generally less precise than digital computers. Slide rule is an example of an analog computer. This book deals only with the digital computer and uses the term computer for them. 1.3 CHARACTERISTICS OF COMPUTER Speed, accuracy, diligence, storage capability and versatility are some of the key characteristics of a computer. A brief overview of these characteristics are—  Speed The computer can process data very fast, at the rate of millions of instructions per second. Some calculations that would have taken hours and days to complete otherwise, can be completed in a few seconds using the computer. For example, calculation and generation of salary slips of thousands of employees of an organization, weather forecasting that requires analysis of a large amount of data related to temperature, pressure and humidity of various places, etc.  Accuracy Computer provides a high degree of accuracy. For example, the computer can accurately give the result of division of any two numbers up to 10 decimal places.  Diligence When used for a longer period of time, the computer does not get tired or fatigued. It can perform long and complex calculations with the same speed and accuracy from the start till the end.  Storage Capability Large volumes of data and information can be stored in the computer and also retrieved whenever required. A limited amount of data can be stored, temporarily, in the primary memory. Secondary storage devices like floppy disk and compact disk can store a large amount of data permanently.   Versatility Computer is versatile in nature. It can perform different types of tasks with the same ease. At one moment you can use the computer to prepare a letter document and in the next moment you may play music or print a document. Computers have several limitations too. Computer can only perform tasks that it has been programmed to do. Computer cannot do any work without instructions from the user. It executes instructions as specified by the user and does not take its own decisions. 1.4 HISTORY OF COMPUTER Until the development of the first generation computers based on vacuum tubes, there had been several developments in the computing technology related to the mechanical computing devices. The key developments that took place till the first computer was developed are as follows—  Calculating Machines ABACUS was the first mechanical calculating device for counting of large numbers. The word ABACUS means calculating board. It consists of bars in horizontal positions on which sets of beads are inserted. The horizontal bars have 10 beads each, representing units, tens, hundreds, etc. An abacus is shown in Figure 1.1 Figure 1.1 Abacus  Napier’s Bones was a mechanical device built for the purpose of multiplication in 1617 ad. by an English mathematician John Napier.  Slide Rule was developed by an English mathematician Edmund Gunter in the 16th century. Using the slide rule, one could perform operations like addition, subtraction, multiplication and division. It was used extensively till late 1970s. Figure 1.2 shows a slide rule.  Figure 1.2 Slide rule  Pascal’s Adding and Subtraction Machine was developed by Blaise Pascal. It could add and subtract. The machine consisted of wheels, gears and cylinders.  Leibniz’s Multiplication and Dividing Machine was a mechanical device that could both multiply and divide. The German philosopher and mathematician Gottfried Leibniz built it around 1673.  Punch Card System was developed by Jacquard to control the power loom in 1801. He invented the punched card reader that could recognize the presence of hole in the punched card as binary one and the absence of the hole as binary zero. The Os and 1s are the basis of the modern digital computer. A punched card is shown in Figure 1.3. Figure 1.3 Punched card  Babbage’s Analytical Engine An English man Charles Babbage built a mechanical machine to do complex mathematical calculations, in the year 1823. The machine was called as difference engine. Later, Charles Babbage and Lady Ada Lovelace developed a general-purpose calculating machine, the analytical engine. Charles Babbage is also called the father of computer.  Hollerith’s Punched Card Tabulating Machine was invented by Herman Hollerith. The machine could read the information from a punched card and process it electronically. The developments discussed above and several others not discussed here, resulted in the development of the first computer in the 1940s. 1.5 GENERATIONS OF COMPUTER The computer has evolved from a large—sized simple calculating machine to a smaller but much more powerful machine. The evolution of computer to the current state is defined in terms of the generations of computer. Each generation of computer is designed based on a new technological development, resulting in better, cheaper and smaller computers that are more powerful, faster and efficient than their predecessors. Currently, there are five generations of computer. In the following subsections, we will discuss the generations of computer in terms of— 1. the technology used by them (hardware and software), 2. computing characteristics (speed, i.e., number of instructions executed per second), 3. physical appearance, and 4. their applications. 1.5.1 First Generation (1940 to 1956): Using Vacuum Tubes  Hardware Technology The first generation of computers used vacuum tubes (Figure 1.4) for circuitry and magnetic drums for memory. The input to the computer was through punched cards and paper tapes. The output was displayed as printouts. Figure 1.4 Vacuum tube  Software Technology The instructions were written in machine language. Machine language uses 0s and 1s for coding of the instructions. The first generation computers could solve one problem at a time.  Computing Characteristics The computation time was in milliseconds.  Physical Appearance These computers were enormous in size and required a large room for installation.  Application They were used for scientific applications as they were the fastest computing device of their time.  Examples UNIVersal Automatic Computer (UNIVAC), Electronic Numerical Integrator And Calculator (ENIAC), and Electronic Discrete Variable Automatic Computer (EDVAC). The first generation computers used a large number of vacuum tubes and thus generated a lot of heat. They consumed a great deal of electricity and were expensive to operate. The machines were prone to frequent malfunctioning and required constant maintenance. Since first generation computers used machine language, they were difficult to program. 1.5.2 Second Generation (1956 to 1963): Using Transistors  Hardware Technology Transistors (Figure 1.5) replaced the vacuum tubes of the first generation of computers. Transistors allowed computers to become smaller, faster, cheaper, energy efficient and reliable. The second generation computers used magnetic core technology for primary memory. They used magnetic tapes and magnetic disks for secondary storage. The input was still through punched cards and the output using printouts. They used the concept of a stored program, where instructions were stored in the memory of computer. Figure 1.5 Transistors  Software Technology The instructions were written using the assembly language. Assembly language uses mnemonics like ADD for addition and SUB for subtraction for coding of the instructions. It is easier to write instructions in assembly language, as compared to writing instructions in machine language. High-level programming languages, such as early versions of COBOL and FORTRAN were also developed during this period.  Computing Characteristics The computation time was in microseconds.  Physical Appearance Transistors are smaller in size compared to vacuum tubes, thus, the size of the computer was also reduced.  Application The cost of commercial production of these computers was very high, though less than the first generation computers. The transistors had to be assembled manually in second generation computers.   Examples PDP-8, IBM 1401 and CDC 1604. Second generation computers generated a lot of heat but much less than the first generation computers. They required less maintenance than the first generation computers. 1.5.3 Third Generation (1964 to 1971): Using Integrated Circuits  Hardware Technology The third generation computers used the Integrated Circuit (IC) chips. Figure 1.6 shows IC chips. In an IC chip, multiple transistors are placed on a silicon chip. Silicon is a type of semiconductor. The use of IC chip increased the speed and the efficiency of computer, manifold. The keyboard and monitor were used to interact with the third generation computer, instead of the punched card and printouts. Figure 1.6 IC chips  Software Technology The keyboard and the monitor were interfaced through the operating system. Operating system allowed different applications to run at the same time. High-level languages were used extensively for programming, instead of machine language and assembly language.  Computing Characteristics The computation time was in nanoseconds.  Physical Appearance The size of these computers was quite small compared to the second generation computers.  Application Computers became accessible to mass audience. Computers were produced commercially, and were smaller and cheaper than their predecessors.  Examples IBM 370, PDP 11. The third generation computers used less power and generated less heat than the second generation computers. The cost of the computer reduced significantly, as individual components of the computer were not required to be assembled manually. The maintenance cost of the computers was also less compared to their predecessors. 1.5.4 Fourth Generation (1971 to present): Using Microprocessors  Hardware Technology They use the Large Scale Integration (LSI) and the Very Large Scale Integration (VLSI) technology. Thousands of transistors are integrated on a small silicon chip using LSI technology. VLSI allows hundreds of thousands of components to be integrated in a small chip. This era is marked by the development of microprocessor. Microprocessor is a chip containing millions of transistors and components, and,  designed using LSI and VLSI technology. A microprocessor chip is shown in Figure 1.7. This generation of computers gave rise to Personal Computer (PC). Semiconductor memory replaced the earlier magnetic core memory, resulting in fast random access to memory. Secondary storage device like magnetic disks became smaller in physical size and larger in capacity. The linking of computers is another key development of this era. The computers were linked to form networks that led to the emergence of the Internet. This generation also saw the development of pointing devices like mouse, and handheld devices. Figure 1.7 Microprocessors  Software Technology Several new operating systems like the MS-DOS and MS- Windows developed during this time. This generation of computers supported Graphical User Interface (GUI). GUI is a user-friendly interface that allows user to interact with the computer via menus and icons. High-level programming languages are used for the writing of programs.  Computing Characteristics The computation time is in picoseconds.  Physical Appearance They are smaller than the computers of the previous generation. Some can even fit into the palm of the hand.  Application They became widely available for commercial purposes. Personal computers became available to the home user.  Examples The Intel 4004 chip was the first microprocessor. The components of the computer like Central Processing Unit (CPU) and memory were located on a single chip. In 1981, IBM introduced the first computer for home use. In 1984, Apple introduced the Macintosh. The microprocessor has resulted in the fourth generation computers being smaller and cheaper than their predecessors. The fourth generation computers are also portable and more reliable. They generate much lesser heat and require less maintenance compared to their predecessors. GUI and pointing devices facilitate easy use and learning on the computer. Networking has resulted in resource sharing and communication among different computers. 1.5.5 Fifth Generation (Present and Next): Using Artificial Intelligence The goal of fifth generation computing is to develop computers that are capable of learning and self-organization. The fifth generation computers use Super Large Scale Integrated (SLSI) chips that are able to store millions of components on a single chip. These computers have large memory requirements. This generation of computers uses parallel processing that allows several instructions to be executed in parallel, instead of serial execution. Parallel processing results in faster processing speed. The Intel dualcore microprocessor uses parallel processing. The fifth generation computers are based on Artificial Intelligence (AI). They try to simulate the human way of thinking and reasoning. Artificial Intelligence includes areas like Expert System (ES), Natural Language Processing (NLP), speech recognition, voice recognition, robotics, etc. 1.6 CLASSIFICATION OF COMPUTER The digital computers that are available nowadays vary in their sizes and types. The computers are broadly classified into four categories (Figure 1.8) based on their size and type—(1) Microcomputers, (2) Minicomputers, (3) Mainframe computers, and (4) Supercomputer. Figure 1.8 Classification of computers based on size and type 1.6.1 Microcomputers Microcomputers are small, low-cost and single-user digital computer. They consist of CPU, input unit, output unit, storage unit and the software. Although microcomputers are stand-alone machines, they can be connected together to create a network of computers that can serve more than one user. IBM PC based on Pentium microprocessor and Apple Macintosh are some examples of microcomputers. Microcomputers include desktop computers, notebook computers or laptop, tablet computer, handheld computer, smart phones and netbook, as shown in Figure 1.9. Figure 1.9 Microcomputers  Desktop Computer or Personal Computer (PC) is the most common type of microcomputer. It is a stand-alone machine that can be placed on the desk. Externally, it consists of three units—keyboard, monitor, and a system unit containing the CPU, memory, hard disk drive, etc. It is not very expensive and is suited to the needs of a single user at home, small business units, and organizations. Apple, Microsoft, HP, Dell and Lenovo are some of the PC manufacturers.  Notebook Computers or Laptop resemble a notebook. They are portable and have all the features of a desktop computer. The advantage of the laptop is that it is small in size (can be put inside a briefcase), can be carried anywhere, has a battery backup and has all the functionality of the desktop. Laptops can be placed on the lap while working (hence the name). Laptops are costlier than the desktop machines.  Netbook These are smaller notebooks optimized for low weight and low cost, and are designed for accessing web-based applications. Starting with the earliest netbook in late 2007, they have gained significant popularity now. Netbooks deliver the performance needed to enjoy popular activities like streaming videos or music, emailing, Web surfing or instant messaging. The word netbook was created as a blend of Internet and notebook.   Tablet Computer has features of the notebook computer but it can accept input from a stylus or a pen instead of the keyboard or mouse. It is a portable computer. Tablet computer are the new kind of PCs.  Handheld Computer or Personal Digital Assistant (PDA) is a small computer that can be held on the top of the palm. It is small in size. Instead of the keyboard, PDA uses a pen or a stylus for input. PDAs do not have a disk drive. They have a limited memory and are less powerful. PDAs can be connected to the Internet via a wireless connection. Casio and Apple are some of the manufacturers of PDA. Over the last few years, PDAs have merged into mobile phones to create smart phones.  Smart Phones are cellular phones that function both as a phone and as a small PC. They may use a stylus or a pen, or may have a small keyboard. They can be connected to the Internet wirelessly. They are used to access the electronic-mail, download music, play games, etc. Blackberry, Apple, HTC, Nokia and LG are some of the manufacturers of smart phones. 1.6.2 Minicomputers Minicomputers (Figure 1.10) are digital computers, generally used in multi-user systems. They have high processing speed and high storage capacity than the microcomputers. Minicomputers can support 4–200 users simultaneously. The users can access the minicomputer through their PCs or terminal. They are used for real-time applications in industries, research centers, etc. PDP 11, IBM (8000 series) are some of the widely used minicomputers. Figure 1.10 Minicomputer 1.6.3 Mainframe Computers Mainframe computers (Figure 1.11) are multi-user, multi-programming and high performance computers. They operate at a very high speed, have very large storage capacity and can handle the workload of many users. Mainframe computers are large and powerful systems generally used in centralized databases. The user accesses the mainframe computer via a terminal that may be a dumb terminal, an intelligent terminal or a PC. A dumb terminal cannot store data or do processing of its own. It has the input and output device only. An intelligent terminal has the input and output device, can do processing, but, cannot store data of its own. The dumb and the intelligent terminal use the processing power and the storage facility of the mainframe computer. Mainframe computers are used in organizations like banks or companies, where many people require frequent access to the same data. Some examples of mainframes are CDC 6600 and IBM ES000 series. Figure 1.11 Mainframe computer 1.6.4 Supercomputers Supercomputers (Figure 1.12) are the fastest and the most expensive machines. They have high processing speed compared to other computers. The speed of a supercomputer is generally measured in FLOPS (FLoating point Operations Per Second). Some of the faster supercomputers can perform trillions of calculations per second. Supercomputers are built by interconnecting thousands of processors that can work in parallel. Supercomputers are used for highly calculation-intensive tasks, such as, weather forecasting, climate research (global warming), molecular research, biological research, nuclear research and aircraft design. They are also used in major universities, military agencies and scientific research laboratories. Some examples of supercomputers are IBM Roadrunner, IBM Blue gene and Intel ASCI red. PARAM is a series of supercomputer assembled in India by C-DAC (Center for Development of Advanced Computing), in Pune. PARAM Padma is the latest machine in this series. The peak computing power of PARAM Padma is 1 Tera FLOP (TFLOP). Figure 1.12 Supercomputer 1.7 THE COMPUTER SYSTEM Computer is an electronic device that accepts data as input, processes the input data by performing mathematical and logical operations on it, and gives the desired output. The computer system consists of four parts (1) Hardware, (2) Software, (3) Data, and (4) Users. The parts of computer system are shown in Figure 1.13. Hardware consists of the mechanical parts that make up the computer as a machine. The hardware consists of physical devices of the computer. The devices are required for input, output, storage and processing of the data. Keyboard, monitor, hard disk drive, floppy disk drive, printer, processor and motherboard are some of the hardware devices. Figure 1.13 Parts of computer system Software is a set of instructions that tells the computer about the tasks to be performed and how these tasks are to be performed. Program is a set of instructions, written in a language understood by the computer, to perform a specific task. A set of programs and documents are collectively called software. The hardware of the computer system cannot perform any task on its own. The hardware needs to be instructed about the task to be performed. Software instructs the computer about the task to be performed. The hardware carries out these tasks. Different software can be loaded on the same hardware to perform different kinds of tasks. Data are isolated values or raw facts, which by themselves have no much significance. For example, the data like 29, January, and 1994 just represent values. The data is provided as input to the computer, which is processed to generate some meaningful information. For example, 29, January and 1994 are processed by the computer to give the date of birth of a person. Users are people who write computer programs or interact with the computer. They are also known as skinware, liveware, humanware or peopleware. Programmers, data entry operators, system analyst and computer hardware engineers fall into this category. 1.7.1 The Input-Process-Output Concept A computer is an electronic device that (1) accepts data, (2) processes data, (3) generates output, and (4) stores data. The concept of generating output information from the input 4 data is also referred to as input-process-output concept. The input-process-output concept of the computer is explained as follows—  Input The computer accepts input data from the user via an input device like keyboard. The input data can be characters, word, text, sound, images, document, etc.  Process The computer processes the input data. For this, it performs some actions on the data by using the instructions or program given by the user of the data. The action could be an arithmetic or logic calculation, editing, modifying a document, etc. During processing, the data, instructions and the output are stored temporarily in the computer’s main memory.  Output The output is the result generated after the processing of data. The output may be in the form of text, sound, image, document, etc. The computer may display the output on a monitor, send output to the printer for printing, play the output, etc.  Storage The input data, instructions and output are stored permanently in the secondary storage devices like disk or tape. The stored data can be retrieved later, whenever needed. 1.7.2 Components of Computer Hardware The computer system hardware comprises of three main components — 1. Input/Output (I/O) Unit, 2. Central Processing Unit (CPU), and 3. Memory Unit. The I/O unit consists of the input unit and the output unit. CPU performs calculations and processing on the input data, to generate the output. The memory unit is used to store the data, the instructions and the output information. Figure 1.14 illustrates the typical interaction among the different components of the computer. Figure 1.14 The computer system interaction   Input/Output Unit The user interacts with the computer via the I/O unit. The Input unit accepts data from the user and the Output unit provides the processed data i.e. the information to the user. The Input unit converts the data that it accepts from the user, into a form that is understandable by the computer. Similarly, the Output unit provides the output in a form that is understandable by the user. The input is provided to the computer using input devices like keyboard, trackball and mouse. Some of the commonly used output devices are monitor and printer.  Central Processing Unit CPU controls, coordinates and supervises the operations of the computer. It is responsible for processing of the input data. CPU consists of Arithmetic Logic Unit (ALU) and Control Unit (CU). o ALU performs all the arithmetic and logic operations on the input data. o CU controls the overall operations of the computer i.e. it checks the sequence of execution of instructions, and, controls and coordinates the overall functioning of the units of computer. Additionally, CPU also has a set of registers for temporary storage of data, instructions, addresses and intermediate results of calculation.  Memory Unit Memory unit stores the data, instructions, intermediate results and output, temporarily, during the processing of data. This memory is also called the main memory or primary memory of the computer. The input data that is to be processed is brought into the main memory before processing. The instructions required for processing of data and any intermediate results are also stored in the main memory. The output is stored in memory before being transferred to the output device. CPU can work with the information stored in the main memory. Another kind of storage unit is also referred to as the secondary memory of the computer. The data, the programs and the output are stored permanently in the storage unit of the computer. Magnetic disks, optical disks and magnetic tapes are examples of secondary memory. 1.8 APPLICATION OF COMPUTERS Computers have proliferated into various areas of our lives. For a user, computer is a tool that provides the desired information, whenever needed. You may use computer to get information about the reservation of tickets (railways, airplanes and cinema halls), books in a library, medical history of a person, a place in a map, or the dictionary meaning of a word. The information may be presented to you in the form of text, images, video clips, etc. Figure 1.15 shows some of the applications of computer. Some of the application areas of the computer are listed below—  Education Computers are extensively used, as a tool and as an aid, for imparting education. Educators use computers to prepare notes and presentations of their lectures. Computers are used to develop computer-based training packages, to provide distance education using the e-learning software, and to conduct online examinations. Researchers use computers to get easy access to conference and journal details and to get global access to the research material.  Entertainment Computers have had a major impact on the entertainment industry. The user can download and view movies, play games, chat, book tickets for cinema halls, use multimedia for making movies, incorporate visual and sound effects using computers, etc. The users can also listen to music, download and share music, create music using computers, etc.  Sports A computer can be used to watch a game, view the scores, improve the game, play games (like chess, etc.) and create games. They are also used for the purposes of training players.  Advertising Computer is a powerful advertising media. Advertisement can be displayed on different websites, electronic-mails can be sent and reviews of a product by different customers can be posted. Computers are also used to create an advertisement using the visual and the sound effects. For the advertisers, computer is a medium via which the advertisements can be viewed globally. Web advertising has become a significant factor in the marketing plans of almost all companies. In fact, the business model of Google is mainly dependent on web advertising for generating revenues. Figure 1.15 Applications of computer  Medicine Medical researchers and practitioners use computers to access information about the advances in medical research or to take opinion of doctors globally. The medical history of patients is stored in the computers. Computers are also an integral part of various kinds of sophisticated medical equipments like ultrasound machine, CAT scan machine, MRI scan machine, etc. Computers also provide assistance to the medical surgeons during critical surgery operations like laparoscopic operations, etc.  Science and Engineering Scientists and engineers use computers for performing complex scientific calculations, for designing and making drawings (CAD/CAM applications) and also for simulating and testing the designs. Computers are used for storing the complex data, performing complex calculations and for visualizing 3–  dimensional objects. Complex scientific applications like the launch of the rockets, space exploration, etc., are not possible without the computers.  Government The government uses computers to manage its own operations and also for e-governance. The websites of the different government departments provide information to the users. Computers are used for the filing of income tax return, paying taxes, online submission of water and electricity bills, for the access of land record details, etc. The police department uses computers to search for criminals using fingerprint matching, etc.  Home Computers have now become an integral part of home equipment. At home, people use computers to play games, to maintain the home accounts, for communicating with friends and relatives via Internet, for paying bills, for education and learning, etc. Microprocessors are embedded in house hold utilities like, washing machines, TVs, food processors, home theatres, security devices, etc. The list of applications of computers is so long that it is not possible to discuss all of them here. In addition to the applications of the computers discussed above, computers have also proliferated into areas like banks, investments, stock trading, accounting, ticket reservation, military operations, meteorological predictions, social networking, business organizations, police department, video conferencing, telepresence, book publishing, web newspapers, and information sharing. SUMMARY  Computer is an electronic device which accepts data as input, performs processing on the data, and gives the desired output. A computer may be analog or digital computer.  Speed, accuracy, diligence, storage capability and versatility are the main characteristics of computer.  The computing devices have evolved from simple mechanical machines, like ABACUS, Napier’s bones, Slide Rule, Pascal’s Adding and Subtraction Machine, Leibniz’s Multiplication and Dividing Machine, Jacquard Punched Card System, Babbage’s Analytical Engine and Hollerith’s Tabulating Machine, to the first electronic computer.  Charles Babbage is called the father of computer.  The evolution of computers to their present state is divided into five generations of computers, based on the hardware and software they use, their physical appearance and their computing characteristics.  First generation computers were vacuum tubes based machines. These were large in size, expensive to operate and instructions were written in machine language. Their computation time was in milliseconds.  Second generation computers were transistor based machines. They used the stored program concept. Programs were written in assembly language. They were smaller in size, less expensive and required less maintenace than the first generation computers. The computation time was in microseconds.  Third generation computers were characterized by the use of IC. They consumed less power and required low maintenance compared to their predecessors. High-level languages were used for programming. The computation time was in nanoseconds. These computers were produced commercially.  Fourth generation computers used microprocessors which were designed using the LSI and VLSI technology. The computers became small, portable, reliable and cheap. The  computation time is in picoseconds. They became available both to the home user and for commercial use.  Fifth generation computers are capable of learning and self organization. These computers use SLSI chips and have large memory requirements. They use parallel processing and are based on AI. The fifth generation computers are still being developed.  Computers are broadly classified as microcomputers, minicomputers, mainframe computers, and supercomputers, based on their sizes and types.  Microcomputers are small, low-cost standalone machines. Microcomputers include desktop computers, notebook computers or laptop, netbooks, tablet computer, handheld computer and smart phones.  Minicomputers are high processing speed machines having more storage capacity than the microcomputers. Minicomputers can support 4–200 users simultaneously.  Mainframe computers are multi-user, multiprogramming and high performance computers. They have very high speed, very large storage capacity and can handle large workloads. Mainframe computers are generally used in centralized databases.  Supercomputers are the most expensive machines, having high processing speed capable of performing trillions of calculations per second. The speed of a supercomputer is measured in FLOPS. Supercomputers find applications in computing-intensive tasks.  Computer is an electronic device based on the input-process-output concept. Input/Output Unit, CPU and Memory unit are the three main components of computer.  Input/Output Unit consists of the Input unit which accepts data from the user and the Output unit that provides the processed data. CPU processes the input data, and, controls, coordinates and supervises the operations of the computer. CPU consists of ALU, CU and Registers. The memory unit stores programs, data and output, temporarily, during the processing. Additionally, storage unit or secondary memory is used for the storing of programs, data and output permanently.  Computers are used in various areas of our life. Education, entertainment, sports, advertising, medicine, science and engineering, government, office and home are some of the application areas of the computers. KEYWORDS ABACUS Input/Output Unit Process Analog computer Integrated Circuit (IC) Program Arithmetic Logic Unit (ALU) Intelligent terminal Punched cards Assembly language Jacquard’s punch card Second Generation Babbage’s Analytical Engine Large Scale Integration (LSI) Computer Central Processing Unit Leibniz’s Machine Slide Rule (CPU) Machine language Smart phones Computer Mainframe computers Software Control Unit (CU) Memory Storage unit Data Microcomputers Supercomputer Desktop computer Microprocessor Super Large Scale Integrated Digital computer Minicomputers (SLSI) chips Dumb terminal Napier’s bones Tablet computer Fifth Generation Computer Netbook Third Generation First Generation Computer Notebook computer Computer Floating point Operations Output Transistors Per Second (FLOPS) Parallel processing Users Fourth Generation Computer Pascal’s Machine Vacuum Tubes Hardware Personal Computer (PC) Very Large Scale Integration Hollerith’s tabulator Personal Digital Assistant (VLSI) Input (PDA) QUESTIONS Section 1.2 1. Define an analog computer and a digital computer. 2. Give an example each of analog computer and digital computer. Section 1.3 3. List the main characteristics of the computer. 4. Describe the characteristics of the computer. 5. List three significant limitations of the computer. Section 1.4 6. Explain briefly the developments in computer technology starting from a simple calculating machine to the first computer. 7. What is a calculating machine? 8. What is the key feature of the Jacquard’s punch card? 9. Name the first calculating device for the counting of large numbers. 10. Who is called the Father of Computer? Section 1.5.1 11. The first generation computers used_____for circuitry. 12. Describe the first generation computer based on the (a) Hardware (b) Software (c) Computing characteristics (d) Physical appearance, and (e) Their applications. 13. Give two examples of first generation computers. 14. List the drawbacks of the first generation computers. Section 1.5.2 15. The second generation computers used_____for circuitry. 16. Describe the second generation computer based on the (a) Hardware (b) Software (c) Computing characteristics (d) Physical appearance and (e) Their applications. 17. Give two examples of second generation computers. 18. List the drawbacks of the second generation computers. Section 1.5.3 19. The third generation computers used_____for circuitry. 20. Describe the third generation computer based on the (a) Hardware (b) Software (c) Computing characteristics (d) Physical appearance, and (e) Their applications. 21. Give two examples of third generation computers. 22. List the drawbacks of the third generation computers. Section 1.5.4 23. The fourth generation computers used_____for circuitry. 24. Describe the fourth generation computer based on the (a) Hardware (b) Software (c) Computing characteristics (d) Physical appearance and (e) Their applications. 25. Give two examples of fourth generation computers. 26. List the drawbacks of the fourth generation computers. Section 1.5.5 27. The fifth generation computers used_____for circuitry. 28. Describe the fifth generation computer based on the (a) Hardware (b) Software (c) Computing characteristics (d) Physical appearance and (e) Their applications. 29. Give two examples of fifth generation computers. 30. Compare in detail the five generations of computers based on the (a) Hardware (b) Software (c) Computing characteristics (d) Physical appearance and (e) Their applications. Also give at least one example of each generation of computer. Section 1.6.1 31. Define microcomputer. 32. Give two examples of microcomputer. 33. List three categories of microcomputers. Section 1.6.2 34. Define minicomputers. 35. Give two examples of minicomputer. Section 1.6.3 36. Define mainframe computer. 37. Give two examples of mainframe computer. 38. Define a dumb terminal. 39. Define an intelligent terminal. Section 1.6.4 40. Define a supercomputer. 41. Give two examples of supercomputer. 42. The speed of supercomputer is generally measured in_____. 43. List two uses of the supercomputer. 44. Name the supercomputer assembled in India. 45. Highlight the differences between microcomputer, minicomputer, mainframe computer and supercomputer. Section 1.7 46. Define a computer. 47. Define (1) Program (2) Software (3) Hardware (4) ALU (5) CU (6) CPU (7) Data. 48. Differentiate between software, data and hardware. 49. List the components of computer hardware. 50. Explain in detail the components of computer hardware. 51. List the steps in the working of the computer. 52. Explain the working of the computer. 53. Explain the input-process-output cycle. Section 1.8 54. List some areas where the computers are used. 55. Explain briefly the use of computers in the following areas—(a) Education, (b) Advertising, and (c) Government. Extra Questions 56. Give full form of the following abbreviations 1. CPU 2. I/O 3. ALU 4. CU 5. LSI 6. VLSI 7. PC 8. GUI 9. SLSI 10. ES 11. NLP 12. AI 13. PDA 14. FLOPS 15. UNIVAC 16. ENIAC 17. EDVAC 57. Write short notes on  1. Components of Computer 2. Input-Process-Output 3. I/O Unit 4. Central Processing Unit 5. Storage Unit 6. History of Computers 7. First Generation Computer 8. Second Generation Computer 9. Third Generation Computer 10. Fourth Generation Computer 11. Fifth Generation Computer 12. Microcomputers 13. Minicomputers 14. Mainframe Computers 15. Supercomputer 16. Personal Computer (PC) 17. Notebook Computer 18. Tablet Computer 19. Netbook 20. Personal Digital Assistant (PDA) 21. Applications of Computer 58. Give differences between the following: 1. Analog and Digital Computer 2. Dumb Terminal and Intelligent Terminal 3. Microcomputer and Minicomputer 4. Minicomputer and Mainframe Computer 5. Mainframe computer and Supercomputer 6. First Generation Computers and Second Generation Computers 7. Second Generation Computers and Third Generation Computers 8. Third Generation Computers and Fourth Generation Computers 9. Fourth Generation Computers and Fifth Generation Computers 10. Desktop Computer and Notebook Computer 2 THE COMPUTER SYSTEM HARDWARE Contents  Central Processing Unit (CPU)  o Arithmetic logic unit o Registers o Control Unit (CU)  Memory unit o Cache memory o Primary memory o Secondary memory  Instruction format  Instruction set  Instruction cycle—Fetching, decoding,executing, storing  Microprocessor—CISC, RISC  Interconnecting the units of a computer— System bus, expansion bus, external ports  Performance of a computer—Registers, RAM, system clock, bus, cache memory  Inside a computer cabinet—Motherboard, ports and interfaces, expansion slots, ribbon cables, memory chips,storage devices, processor Why this chapter The computer as a machine consists of different components that interact with each other to provide the desired functionality of the computer. As a user of the computer, we need to be aware of the main components of the computer, their functions and the interconnection between the different components of the computer. This chapter describes the different hardware components of the computer. 2.1 INTRODUCTION When we talk of computer hardware, the three related terms that require introduction are— computer architecture, computer organization and computer design. Computer architecture refers to the structure and behavior of the computer. It includes the specifications of the components, for example, instruction format, instruction set and techniques for addressing memory, and how they connect to the other components. Given the components, computer organization focuses on the organizational structure. It deals with how the hardware components operate and the way they are connected to form the computer. Given the system specifications, computer design focuses on the hardware to be used and the interconnection of parts. Different kinds of computer, such as a PC or a mainframe computer may have different organization; however, basic organization of the computer remains the same. A computer consists of three main components—(1) Input/Output (I/O) Unit, (2) Central Processing Unit (CPU), and (3) Memory Unit. The computer user interacts with the computer via the I/O unit. The purpose of I/O unit is to provide data and instructions as input to the computer and to present relevant information as output from the computer. CPU controls the operations of the computer and processes the received input to generate the relevant output. The memory unit stores the instructions and the data during the input activity, to make instructions readily available to CPU during processing. It also stores the processed output. This chapter discusses the hardware components of the computer and the interaction between them. 2.2 CENTRAL PROCESSING UNIT Central Processing Unit (CPU) or the processor is also often called the brain of computer. CPU (Figure 2.1) consists of Arithmetic Logic Unit (ALU) and Control Unit (CU). In addition, CPU also has a set of registers which are temporary storage areas for holding data, and instructions. ALU performs the arithmetic and logic operations on the data that is made available to it. CU is responsible for organizing the processing of data and instructions. CU controls and coordinates the activity of the other units of computer. CPU uses the registers to store the data, instructions during processing. CPU executes the stored program instructions, i.e. instructions and data are stored in memory before execution. For processing, CPU gets data and instructions from the memory. It interprets the program instructions and performs the arithmetic and logic operations required for the processing of data. Then, it sends the processed data or result to the memory. CPU also acts as an administrator and is responsible for supervising operations of other parts of the computer. The CPU is fabricated as a single Integrated Circuit (IC) chip, and is also known as the microprocessor. The microprocessor is plugged into the motherboard of the computer (Motherboard is a circuit board that has electronic circuit etched on it and connects the microprocessor with the other hardware components). Figure 2.1 CPU 2.2.1 Arithmetic Logic Unit  ALU consists of two units—arithmetic unit and logic unit.  The arithmetic unit performs arithmetic operations on the data that is made available to it. Some of the arithmetic operations supported by the arithmetic unit are—addition, subtraction, multiplication and division.  The logic unit of ALU is responsible for performing logic operations. Logic unit performs comparisons of numbers, letters and special characters. Logic operations include testing for greater than, less than or equal to condition.   ALU performs arithmetic and logic operations, and uses registers to hold the data that is being processed. 2.2.2 Registers  Registers are high-speed storage areas within the CPU, but have the least storage capacity. Registers are not referenced by their address, but are directly accessed and manipulated by the CPU during instruction execution.  Registers store data, instructions, addresses and intermediate results of processing. Registers are often referred to as the CPU’s working memory.  The data and instructions that require processing must be brought in the registers of CPU before they can be processed. For example, if two numbers are to be added, both numbers are brought in the registers, added and the result is also placed in a register.  Registers are used for different purposes, with each register serving a specific purpose. Some of the important registers in CPU (Figure 2.2) are as follows— o Accumulator (ACC) stores the result of arithmetic and logic operations. o Instruction Register (IR) contains the current instruction most recently fetched. o Program Counter (PC) contains the address of next instruction to be processed. o Memory Address Register (MAR) contains the address of next location in the memory to be accessed. o Memory Buffer Register (MBR) temporarily stores data from memory or the data to be sent to memory. o Data Register (DR) stores the operands and any other data. Figure 2.2 CPU registers  The number of registers and the size of each (number of bits) register in a CPU helps to determine the power and the speed of a CPU.  The overall number of registers can vary from about ten to many hundreds, depending on the type and complexity of the processor.  The size of register, also called word size, indicates the amount of data with which the computer can work at any given time. The bigger the size, the more quickly it can process data. The size of a register may be 8, 16, 32 or 64 bits. For example, a 32–bit CPU is one  in which each register is 32 bits wide and its CPU can manipulate 32 bits of data at a time. Nowadays, PCs have 32–bit or 64–bit registers.  32-bit processor and 64-bit processor are the terms used to refer to the size of the registers. Other factors remaining the same, a 64-bit processor can process the data twice as fast as one with 32-bit processor. 2.2.3 Control Unit  The control unit of a computer does not do any actual processing of data. It organizes the processing of data and instructions. It acts as a supervisor and, controls and coordinates the activity of the other units of computer.  CU coordinates the input and output devices of a computer. It directs the computer to carry out stored program instructions by communicating with the ALU and the registers. CU uses the instructions in the Instruction Register (IR) to decide which circuit needs to be activated. It also instructs the ALU to perform the arithmetic or logic operations. When a program is run, the Program Counter (PC) register keeps track of the program instruction to be executed next.  CU tells when to fetch the data and instructions, what to do, where to store the results, the sequencing of events during processing etc.  CU also holds the CPU’s Instruction Set, which is a list of all operations that the CPU can perform. The function of a (CU) can be considered synonymous with that of a conductor of an orchestra. The conductor in an orchestra does not perform any work by itself but manages the orchestra and ensures that the members of orchestra work in proper coordination. 2.3 MEMORY UNIT The memory unit consists of cache memory and primary memory. Primary memory or main memory of the computer is used to store the data and instructions during execution of the instructions. Random Access Memory (RAM) and Read Only Memory (ROM) are the primary memory. In addition to the main memory, there is another kind of storage device known as the secondary memory. Secondary memory is non-volatile and is used for permanent storage of data and programs. A program or data that has to be executed is brought into the RAM from the secondary memory. 2.3.1 Cache Memory  The data and instructions that are required during the processing of data are brought from the secondary storage devices and stored in the RAM. For processing, it is required that the data and instructions are accessed from the RAM and stored in the registers. The time taken to move the data between RAM and CPU registers is large. This affects the speed of processing of computer, and results in decreasing the performance of CPU.  Cache memory is a very high speed memory placed in between RAM and CPU. Cache memory increases the speed of processing.  Cache memory is a storage buffer that stores the data that is used more often, temporarily, and makes them available to CPU at a fast rate. During processing, CPU  first checks cache for the required data. If data is not found in cache, then it looks in the RAM for data.  To access the cache memory, CPU does not have to use the motherboard’s system bus for data transfer. (The data transfer speed slows to the motherboard’s capability, when data is passed through system bus. CPU can process data at a much faster rate by avoiding the system bus.) Figure 2.3 Illustration of cache memory  Cache memory is built into the processor, and may also be located next to it on a separate chip between the CPU and RAM. Cache built into the CPU is faster than separate cache, running at the speed of the microprocessor itself. However, separate cache is roughly twice as fast as RAM.  The CPU has a built-in Level 1 (L1) cache and Level2 (L2) cache, as shown in Figure 2.3. In addition to the built-in L1 and L2 cache, some CPUs have a separate cache chip on the motherboard. This cache on the motherboard is called Level 3 (L3) cache. Nowadays, high-end processor comes with built-in L3 cache, like in Intel core i7. The L1, L2 and L3 cache store the most recently run instructions, the next ones and the possible ones, respectively. Typically, CPUs have cache size varying from 256KB (L1), 6 MB (L2), to 12MB (L3) cache.  Cache memory is very expensive, so it is smaller in size. Generally, computers have cache memory of sizes 256 KB to 2 MB. 2.3.2 Primary Memory  Primary memory is the main memory of computer. It is used to store data and instructions during the processing of data. Primary memory is semiconductor memory.  Primary memory is of two kinds—Random Access Memory (RAM) and Read Only Memory (ROM).  RAM is volatile. It stores data when the computer is on. The information stored in RAM gets erased when the computer is turned off. RAM provides temporary storage for data and instructions.  ROM is non-volatile memory, but is a read only memory. The storage in ROM is permanent in nature, and is used for storing standard processing programs that permanently reside in the computer. ROM comes programmed by the manufacturer.  RAM stores data and instructions during the execution of instructions. The data and instructions that require processing are brought into the RAM from the storage devices  like hard disk. CPU accesses the data and the instructions from RAM, as it can access it at a fast speed than the storage devices connected to the input and output unit (Figure 2.4).  The input data that is entered using the input unit is stored in RAM, to be made available during the processing of data. Similarly, the output data generated after processing is stored in RAM before being sent to the output device. Any intermediate results generated during the processing of program are stored in RAM.  RAM provides a limited storage capacity, due to its high cost. Figure 2.4 Interaction of CPU with memory 2.3.3 Secondary Memory  The secondary memory stores data and instructions permanently. The information can be stored in secondary memory for a long time (years), and is generally permanent in nature unless erased by the user. It is a non-volatile memory.  It provides back-up storage for data and instructions. Hard disk drive, floppy drive and optical disk drives are some examples of storage devices.  The data and instructions that are currently not being used by CPU, but may be required later for processing, are stored in secondary memory.  Secondary memory has a high storage capacity than the primary memory.  Secondary memory is also cheaper than the primary memory.  It takes longer time to access the data and instructions stored in secondary memory than in primary memory. Magnetic tape drives, disk drives and optical disk drives are the different types of storage devices. 2.4 INSTRUCTION FORMAT A computer program is a set of instructions that describe the steps to be performed for carrying out a computational task. The program and the data, on which the program operates, are stored in main memory, waiting to be processed by the processor. This is also called the stored program concept. An instruction is designed to perform a task and is an elementary operation that the processor can accomplish. An instruction is divided into groups called fields. The common fields of an instruction are— Operation (op) code and Operand code (Figure 2.5). The remainder of the instruction fields differs from one computer type to other. The operation code represents action that the processor must execute. It tells the processor what basic operations to perform. The operand code defines the parameters of the action and depends on the operation. It specifies the locations of the data or the operand on which the operation is to be performed. It can be data or a memory address. Figure 2.5 Instruction format Figure 2.6 Instruction format for ADD command The number of bits in an instruction varies according to the type of data (could be between 8 and 32 bits). Figure 2.6 shows the instruction format for ADD command. 2.5 INSTRUCTION SET A processor has a set of instructions that it understands, called as instruction set. An instruction set or an instruction set architecture is a part of the computer architecture. It relates to programming, instructions, registers, addressing modes, memory architecture, etc. An Instruction Set is the set of all the basic operations that a processor can accomplish. Examples of some instructions are shown in Figure 2.7. The instructions in the instruction set are the language that a processor understands. All programs have to communicate with the processor using these instructions. An instruction in the instruction set involves a series of logical operations (may be thousands) that are performed to complete each task. The instruction set is embedded in the processor (hardwired), which determines the machine language for the processor. All programs written in a high-level language are compiled and translated into machine code before execution, which is understood by the processor for which the program has been coded. Figure 2.7 Examples of some instructions Two processors are different if they have different instruction sets. A program run on one computer may not run on another computer having a different processor. Two processors are compatible if the same machine level program can run on both the processors. Therefore, the system software is developed within the processor’s instruction set. Microarchitecture is the processor design technique used for implementing the Instruction Set. Computers having different microarchitecture can have a common Instruction Set. Pentium and Athlon CPU chips implement the x86 instruction set, but have different internal designs. 2.6 INSTRUCTION CYCLE The primary responsibility of a computer processor is to execute a sequential set of instructions that constitute a program. CPU executes each instruction in a series of steps, called instruction cycle (Figure 2.8).  A instruction cycle involves four steps (Figure 2.9)— o Fetching The processor fetches the instruction from the memory. The fetched instruction is placed in the Instruction Register. Program Counter holds the address of next instruction to be fetched and is incremented after each fetch. o Decoding The instruction that is fetched is broken down into parts or decoded. The instruction is translated into commands so that they correspond to those in the CPU’s instruction set. The instruction set architecture of the CPU defines the way in which an instruction is decoded. o Executing The decoded instruction or the command is executed. CPU performs the operation implied by the program instruction. For example, if it is an ADD instruction, addition is performed. o Storing CPU writes back the results of execution, to the computer’s memory.  Figure 2.8 Instruction cycle Figure 2.9 Steps in instruction cycle  Instructions are of different categories. Some categories of instructions are— o Memory access or transfer of data between registers. o Arithmetic operations like addition and subtraction. o Logic operations such as AND, OR and NOT. o Control the sequence, conditional connections, etc. A CPU performance is measured by the number of instructions it executes in a second, i.e., MIPS (million instructions per second), or BIPS (billion instructions per second). 2.7 MICROPROCESSOR A processor’s instruction set is a determining factor in its architecture. On the basis of the instruction set, microprocessors are classified as—Reduced Instruction Set Computer (RISC), and Complex Instruction Set Computer (CISC). The x86 instruction set of the original Intel 8086 processor is of the CISC type. The PCs are based on the x86 instruction set.  CISC architecture hardwires the processor with complex instructions, which are difficult to create otherwise using basic instructions. CISC combines the different instructions into one single CPU. o CISC has a large instruction set that includes simple and fast instructions for performing basic tasks, as well as complex instructions that correspond to statements in the high level language. o An increased number of instructions (200 to 300) results in a much more complex processor, requiring millions of transistors. o Instructions are of variable lengths, using 8, 16 or 32 bits for storage. This results in the processor’s time being spent in calculating where each instruction begins and ends. o With large number of application software programs being written for the processor, a new processor has to be backwards compatible to the older version of processors. o AMD and Cyrix are based on CISC.  RISC has simple, single-cycle instructions, which performs only basic instructions. RISC architecture does not have hardwired advanced functions. All high-level language support is done in the software. o RISC has fewer instructions and requires fewer transistors, which results in the reduced manufacturing cost of processor. o The instruction size is fixed (32 bits). The processor need not spend time in finding out where each instruction begins and ends. o RISC architecture has a reduced production cost compared to CISC processors. o The instructions, simple in nature, are executed in just one clock cycle, which speeds up the program execution when compared to CISC processors. o RISC processors can handle multiple instructions simultaneously by processing them in parallel. o Apple Mac G3 and PowerPC are based on RISC. Processors like Athlon XP and Pentium IV use a hybrid of both technologies. Pipelining improves instruction execution speed by putting the execution steps into parallel. A CPU can receive a single instruction, begin executing it, and receive another instruction before it has completed the first. This allows for more instructions to be performed, about, one instruction per clock cycle. Parallel Processing is the simultaneous execution of instructions from the same program on different processors. A program is divided into multiple processes that are handled in parallel in order to reduce execution time. 2.8 INTERCONNECTING THE UNITS OF A COMPUTER CPU sends data, instructions and information to the components inside the computer as well as to the peripherals and devices attached to it. Bus is a set of electronic signal pathways that allows information and signals to travel between components inside or outside of a computer. The different components of computer, i.e., CPU, I/O unit, and memory unit are connected with each other by a bus. The data, instructions and the signals are carried between the different components via a bus. The features and functionality of a bus are as follows—  A bus is a set of wires used for interconnection, where each wire can carry one bit of data.  A bus width is defined by the number of wires in the bus.  A computer bus can be divided into two types—Internal Bus and External Bus.  The Internal Bus connects components inside the motherboard like, CPU and system memory. It is also called the System Bus. Figure 2.10 shows interaction between processor and memory. Figure 2.10 Interaction between CPU and memory  The External Bus connects the different external devices, peripherals, expansion slots, I/O ports and drive connections to the rest of computer. The external bus allows various devices to be attached to the computer. It allows for the expansion of computer’s capabilities. It is generally slower than the system bus. It is also referred to as the Expansion Bus.  A system bus or expansion bus comprise of three kinds of buses — data bus, address bus and control bus.  The interaction of CPU with memory and I/O devices involves all the three buses. o The command to access the memory or the I/O device is carried by the control bus. o The address of I/O device or memory is carried by the address bus. o The data to be transferred is carried by the data bus. Figure 2.11 shows interaction between processor, memory and the peripheral devices. 2.8.1 System Bus The functions of data bus, address bus and control bus, in the system bus, are as follows—  Data Bus transfers data between the CPU and memory. The bus width of a data bus affects the speed of computer. The size of data bus defines the size of the processor. A processor can be 8, 16, 32 or 64-bit processor. An 8–bit processor has 8 wire data bus to carry 1 byte of data. In a 16–bit processor, 16–wire bus can carry 16 bits of data, i.e., transfer 2 bytes, etc. Figure 2.11 Interaction between CPU, memory and peripheral devices  Address Bus connects CPU and RAM with set of wires similar to data bus. The width of address bus determines the maximum number of memory locations the computer can address. Currently, Pentium Pro, II, III, IV have 36–bit address bus that can address 236 bytes or 64 GB of memory.  Control Bus specifies whether data is to be read or written to the memory, etc. 2.8.2 Expansion Bus The functions of data bus, address bus and control bus, in the expansion bus, are as follows—  The expansion bus connects external devices to the rest of computer. The external devices like monitor, keyboard and printer connect to ports on the back of computer. These ports are actually a part of the small circuit board or expansion card that fits into an expansion slot on the motherboard. Expansion slots are easy to recognize on the motherboard.  Expansion slots make up a row of long plastic connectors at the back of the computer with tiny copper ‘finger slots’ in a narrow channel that grab the connectors on the expansion cards. The slots are attached to tiny copper pathways on the motherboard (the expansion bus), which allows the device to communicate with the rest of computer.  Data Bus is used to transfer data between I/O devices and CPU. The exchange of data between CPU and I/O devices is according to the industry standard data buses. The most commonly used standard is Extended Industry Standard Architecture (EISA) which is a 32-bit bus architecture. Some of the common bus technologies are— o Peripheral Component Interconnect (PCI) bus for hard disks, sound cards, network cards and graphics cards,  o Accelerated Graphics Port (AGP) bus for 3–D and full motion video, o Universal Serial Bus (USB) to connect and disconnect different devices.  Address Bus carries the addresses of different I/O devices to be accessed like the hard disk, CD ROM, etc.  Control Bus is used to carry read/write commands, status of I/O devices, etc. 2.8.3 External Ports The peripheral devices interact with the CPU of the computer via the bus. The connections to the bus from the peripheral devices are made via the ports and sockets provided at the sides of the computer. The different ports and sockets facilitate the connection of different devices to the computer. Some of the standard port connections available on the outer sides of the computer are— port for mouse, keyboard, monitor, network, modem, and, audio port, serial port, parallel port and USB port. The different ports are physically identifiable by their different shapes, size of contact pins and number of pins. Figure 2.12 shows the interaction of serial and parallel port interfaces with the devices. Figure 2.12 Interaction of serial and parallel port interfaces 2.9 PERFORMANCE OF A COMPUTER There are a number of factors involved that are related to the CPU and have an effect on the overall speed and performance of the computer. Some of the factors that affect the performance of the computer include— Figure 2.13 System properties in Windows XP Professional  Registers The size of the register (word size) indicates the amount of data with which the computer can work at any given time. The bigger the size, the more quickly it can process data. A 32–bit CPU is one in which each register is 32 bits wide.  RAM It is used to store data and instructions during execution of the instructions. Anything you do on your computer requires RAM. When the computer is switched on, the operating system, device drivers, the active files and running programs are loaded into RAM. If RAM is less, then the CPU waits each time the new information is swapped into memory from the slower devices. Larger the RAM size, the better it is. PCs nowadays usually have 1 GB to 4 GB of RAM.  System Clock The clock speed of a CPU is defined as the frequency with which a processor executes instructions or the data is processed. Higher clock frequencies mean more clock ticks per second. The computer’s operating speed is linked to the speed of the system clock. The clock frequency is measured in millions of cycles per second or megahertz (MHz) or gigahertz (GHz) which is billions of cycles per second. A CPU’s  performance is measured by the number of instructions it executes in a second, i.e., MIPS or BIPS. PCs nowadays come with a clock speed of more than 1 GHz. In Windows OS, you can select the System Properties dialog box to see the processor name and clock frequency.  Bus Data bus is used for transfering data between CPU and memory. The data bus width affects the speed of computer. In a 16–bit processor, 16–bit wire bus can carry 16 bits of data. The bus speed is measured in MHz. Higher the bus speed the better it is. Address bus connects CPU and RAM with a set of wires similar to data bus. The address bus width determines the maximum number of memory locations the computer can address. Pentium Pro, II, III, IV have 36–bit address bus that can address 236 bytes or 64 GB of memory. PCs nowadays have a bus speed varying from 100 MHz to 400 MHz.  Cache Memory Two of the main factors that affect a cache’s performance are its size (amount of cache memory) and level L1, L2 and L3. Larger the size of cache, the better it is. PCs nowadays have a L1 cache of 256KB and L2 cache of 1MB. Figure 2.13 shows the general information about a computer as displayed in the system properties window in Windows XP Professional. 2.10 INSIDE A COMPUTER CABINET The computer cabinet encloses the components that are required for the running of the computer. The components inside a computer cabinet include the power supply, motherboard, memory chips, expansion slots, ports and interface, processor, cables and storage devices. 2.10.1 Motherboard The computer is built up around a motherboard. The motherboard is the most important component in the PC. It is a large Printed Circuit Board (PCB), having many chips, connectors and other electronics mounted on it. The motherboard is the hub, which is used to connect all the essential components of a computer. The RAM, hard drive, disk drives and optical drives are all plugged into interfaces on the motherboard. The motherboard contains the processor, memory chips, interfaces and sockets, etc. The motherboard may be characterized by the form factor, chipset and type of processor socket used. Form factor refers to the motherboard’s geometry, dimensions, arrangement and electrical requirements. Different standards have been developed to build motherboards, which can be used in different brands of cases. Advanced Technology Extended (ATX) is the most common design of motherboard for desktop computers. Chipset is a circuit, which controls the majority of resources (including the bus interface with the processor, cache memory and RAM, expansion cards, etc.) Chipset’s job is to coordinate data transfers between the various components of the computer (including the processor and memory). As the chipset is integrated into the motherboard, it is important to choose a motherboard, which includes a recent chipset, in order to maximize the computer’s upgradeability. The processor socket may be a rectangular connector into which the processor is mounted vertically (slot), or a square-shaped connector with many small connectors into which the processor is directly inserted (socket). The Basic Input Output System (BIOS) and Complementary Metal-Oxide Semiconductor (CMOS) are present on the motherboard. Figure 2.14 ROM BIOS  BIOS It is the basic program used as an interface between the operating system and the motherboard. The BIOS (Figure 2.14) is stored in the ROM and cannot be rewritten. When the computer is switched on, it needs instructions to start. BIOS contain the instructions for the starting up of the computer. The BIOS runs when the computer is switched on. It performs a Power On Self Test (POST) that checks that the hardware is functioning properly and the hardware devices are present. It checks whether the operating system is present on the hard drive. BIOS invokes the bootstrap loader to load the operating system into memory. BIOS can be configured using an interface named BIOS setup, which can be accessed when the computer is booting up (by pressing the DEL key).  CMOS Chip BIOS ROMs are accompanied by a smaller CMOS (CMOS is a type of memory technology) memory chip. When the computer is turned off, the power supply stops providing electricity to the motherboard. When the computer is turned on again, the system still displays the correct clock time. This is because the CMOS chip saves some system information, such as time, system date and essential system settings. CMOS is kept powered by a button battery located on the motherboard (Figure 2.15). The CMOS chip is working even when the computer power is switched off. Information of the hardware installed in the computer (such as the number of tracks or sectors on each hard drive) is stored in the CMOS chip. Figure 2.15 Battery for CMOS chip 2.10.2 Ports and Interfaces Motherboard has a certain number of I/O sockets that are connected to the ports and interfaces found on the rear side of a computer (Figure 2.16). You can connect external devices to the ports and interfaces, which get connected to the computer’s motherboard.  Serial Port— to connect old peripherals.  Parallel Port— to connect old printers. Figure 2.16 Ports on the rear side of a PC  USB Ports—to connect newer peripherals like cameras, scanners and printers to the computer. It uses a thin wire to connect to the devices, and many devices can share that wire simultaneously.  Firewire is another bus, used today mostly for video cameras and external hard drives.  RJ45 connector (called LAN or Ethernet port) is used to connect the computer to a network. It corresponds to a network card integrated into the motherboard.  VGA connector for connecting a monitor. This connector interfaces with the built-in graphics card.  Audio plugs (line-in, line-out and microphone), for connecting sound speakers and the microphone. This connector interfaces with the built-in sound card.  PS/2 port to connect mouse and keyboard into PC.  SCSI port for connecting the hard disk drives and network connectors. 2.10.3 Expansion Slots The expansion slots (Figure 2.17) are located on the motherboard. The expansion cards are inserted in the expansion slots. These cards give the computer new features or increased performance. There are several types of slots:  ISA (Industry Standard Architecture) slot—To connect modem and input devices.  PCI (Peripheral Component InterConnect) slot—To connect audio, video and graphics. They are much faster than ISA cards.  AGP (Accelerated Graphic Port) slot—A fast port for a graphics card.  PCI (Peripheral Component InterConnect) Express slot—Faster bus architecture than AGP and PCI buses.  PC Card—It is used in laptop computers. It includes Wi-Fi card, network card and external modem.  Figure 2.17 Expansion slots 2.10.4 Ribbon Cables Ribbon cables (Figure 2.18) are flat, insulated and consist of several tiny wires moulded together that carry data to different components on the motherboard. There is a wire for each bit of the word or byte and additional wires to coordinate the activity of moving information. They also connect the floppy drives, disk drives and CD-ROM drives to the connectors in the motherboard. Nowadays, Serial Advanced Technology Attachment (SATA) cables have replaced the ribbon cables to connect the drives to the motherboard. Figure 2.18 Ribbon cables inside a PC 2.10.5 Memory Chips The RAM consists of chips on a small circuit board (Figure 2.19). Two types of memory chips— Single In-line Memory Module (SIMM) and Dual In-line Memory Module (DIMM) are used in desktop computers. The CPU can retrieve information from DIMM chip at 64 bits compared to 32 bits or 16 bits transfer with SIMM chips. DIMM chips are used in Pentium 4 onwards to increase the access speed. Figure 2.19 RAM memory chip 2.10.6 Storage Devices The disk drives are present inside the machine. The common disk drives in a machine are hard disk drive, floppy drive (Figure 2.20 (i & ii)) and CD drive or DVD drive. High-storage devices like hard disk, floppy disk and CDs (Figure 2.20 (iii) & (iv)) are inserted into the hard disk drive, floppy drive and CD drive, respectively. These storage devices can store large amounts of data, permanently. 2.10.7 Processor The processor or the CPU is the main component of the computer. Select a processor based on factors like its speed, performance, reliability and motherboard support. Pentium Pro, Pentium 2 and Pentium 4 are some of the processors. Figure 2.20 Storage devices (i) Hard disk drive, (ii) DVD drive, (iii) Floppy disk, (iv) CD SUMMARY  Different computers may have different organization, but the basic organization of the computer remains the same.  I/O Unit, CPU and Memory Unit are the main components of the computer.  CPU or microprocessor is called the brain of the computer. It processes the data and the instructions. It also supervises the operations of other parts of the computer.  Registers, Arithmetic Logic Unit and Control Unit are the parts of CPU.  Cache memory, primary memory and secondary memory constitute the memory unit. Primary memory consists of RAM and ROM.  Registers are low-storage capacity, high-speed storage areas within the CPU. The data, instructions, addresses and intermediate results of processing are stored in the registers by the CPU.  Cache memory is a very high-speed memory placed in between RAM and CPU, to increase the processing speed. Cache memory is available in three levels L1, L2 and L3.  RAM provides temporary storage, has a limited storage capacity and is volatile memory. The access speed of RAM is faster than access speed of the storage devices like hard disk. The data and the instructions stored in the hard disk are brought into the RAM so that the CPU can access the data and the instructions and process it.  CU organizes the processing of data and instructions. It acts as a supervisor and controls and coordinates the activity of other units of computer.  ALU performs arithmetic operations and logic operations on the data.  An instruction is an elementary operation that the processor can accomplish. The instructions in the instruction set are the language that a processor understands. The instruction set is embedded in the processor which determines the machine language for the processor.  A CPU instruction cycle involves four steps— (1) Fetching the instructions from the memory, (2) Decoding instructions so that they correspond to those in the CPU’s instruction set, (3) Executing the decoded instructions, and (4) Storing the result to the computer memory.  RISC and CISC are the two kinds of microprocessors classified on the basis of the instruction set. CISC has a large and complex instruction set. RISC has fewer instructions.  The different components of computer are connected with each other by a bus. A computer bus is of two types—system bus and expansion bus. A system bus or expansion bus comprise of three kinds of buses— data bus, address bus and control bus.  The System Bus connects the CPU, system memory, and all other components on the motherboard.  The Expansion Bus connects the different external devices, peripherals, expansion slots, I/O ports and drive connections to the rest of the computer.  The performance of the computer is affected by the size of registers, size of RAM, speed of system clock, width of bus, and size of cache memory.  Inside a computer cabinet, there is a motherboard, ports and interfaces, expansion slots, ribbon cables, RAM memory chips, high storage disk drives, and, processor.  The motherboard is characterized by the form factor, chipset and type of processor socket. Form factor is the motherboard’s geometry, dimensions, arrangement and electrical requirements. Chipset controls the majority of resources of the computer.  BIOS and CMOS are present on the motherboard. BIOS is stored in ROM and is used as an interface between the operating system and the motherboard. The time, the system date, and essential system settings are saved in CMOS memory chip present on the motherboard. When the computer power is switched off, CMOS chip remains alive powered by a button battery.  Ports and interfaces are located on the sides of the computer case to which the external devices can be connected. Some of the ports and interfaces are— Serial port, Parallel  port, USB port, Firewire, RJ45 connector, VGA connector, Audio plugs, PS/2 port, and SCSI port. KEYWORDS Accelerated Graphics Port CPU performance Peripheral Component (AGP) Data bus Interconnect (PCI) Address bus Decoding Power On Self Test (POST) Arithmetic Logic Unit (ALU) Executing Primary memory Audio plugs Expansion bus PS/2 Port Basic Input Output System Expansion card Random Access Memory (BIOS) Expansion slot (RAM) Billion Instructions Per Second Extended Industry Standard Read Only Memory (ROM) (BIPS) Architecture (EISA) Reduced Instruction Set Brain of computer Fetching Computer (RISC) Bus Firewire Registers Cache memory Form factor Ribbon cables Central Processing Unit (CPU) Input/Output (I/O) unit SCSI port Chipset Instruction format Serial port Complementary Metal-Oxide Instruction set Speed of computer Semiconductor (CMOS) Instruction cycle Stored program Complex Instruction Set Memory Unit Storing Computer (CISC) Microprocessor System bus Computer architecture Million Instructions Per System clock Second Computer design (MIPS) Universal Serial Bus Computer organization Motherboard (USB) Control bus Parallel port Word size Control Unit (CU) QUESTIONS Section 2.1 1. Define computer architecture, computer organization and computer design. 2. Give a brief description of the working of the computer. Section 2.2 3. CPU is also often called the_____of computer. 4. Define a microprocessor. 5. Define a motherboard. 6. The different parts of the CPU are_____, _____ and _____. 7. _____ and _____ are the main memory. 8. What is the purpose of the main memory? 9. List the main functions of the CPU. Section 2.2.1–2.2.3 10. ALU consists of the _____ unit and _____ unit. 11. What are the functions of the ALU? 12. _____ is also called the working memory of the CPU. 13. List five important registers of the CPU. Also state the purpose of each register. 14. Why are Registers used in the CPU? 15. Define word size. 16. “This is a 64–bit processor”. Explain its meaning. 17. The size of the register is also the _____ size. 18. Which is faster—a 32-bit processor or a 64-bit- processor? 19. What are the functions of the control unit? Section 2.3–2.3.3 20. Explain the need of the cache memory? 21. The _____ memory is placed between the RAM and the CPU. 22. There are _____ levels of cache memory. 23. Explain the three levels of the cache memory. 24. State three important features of the cache memory. 25. The size of the cache memory is generally in the range _____. 26. What is the purpose of RAM? 27. List the features of the primary memory. 28. List the key features of the secondary memory. Section 2.4 29. Define the stored program concept. 30. Describe the format of an instruction. 31. The common fields of an instruction are _____ code and _____ code. 32. What is the function of the operand code and the operation code? Section 2.5 33. Define an Instruction set. 34. What is the significance of the Instruction set in the CPU? 35. “Two processors are compatible”. How do you deduce this statement? 36. Define microarchitecture. Section 2.6 37. Define an instruction cycle. 38. Give a detailed working of the instruction cycle. 39. Name the four steps involved in an instruction cycle. 40. The number of instructions executed in a second by the CPU, is measured in _____. Section 2.7 41. The microprocessors are classified as _____ and _____ on the basis of the instruction set. 42. The x86 instruction set of the original Intel 8086 processor is of the _____ type. 43. Describe the features of the CISC architecture. 44. Give two examples of the CISC processor. 45. Describe the features of the RISC architecture. 46. Give two examples of the RISC processor. 47. What is the use of parallel processing and pipelining? Section 2.8 48. Define a bus. 49. Define a system bus. 50. Define an expansion bus. 51. Why is a bus used? 52. Define—control bus, address bus and data bus. 53. A system bus or expansion bus comprises of three kinds of buses _____, _____ and _____. 54. Name the bus connecting CPU with memory? 55. Name the bus connecting I/O devices with CPU? Section 2.8.1 56. In a system bus, what is the significance of the control bus, address bus and data bus? 57. The _____ of data bus affects the speed of computer. 58. Name the bus whose width affects the speed of computer? 59. The _____ of address bus determines the maximum number of memory locations the computer can address. 60. Name the bus whose width determines the maximum number of memory locations the computer can address? Section 2.8.2–2.8.3 61. What are the functions of data bus, address bus and control bus in the expansion bus? 62. Where is the expansion card fixed on the motherboard? 63. What is an expansion slot? 64. Name three common bus technologies. 65. What kind of devices is attached to the PCI bus, AGP bus and USB bus? Section 2.9 66. List the factors that affect the performance of the computer. 67. Explain in detail the factors that affect the performance of the computer. 68. What is the use of the system clock? 69. The clock frequency is measured in _____. Section 2.10–2.10.1 70. “The motherboard is characterized by the form factor, chipset and the type of processor socket used”. Explain. 71. Define form factor. 72. Define chipset. 73. _____ is the most common design of the motherboard for desktop computers. 74. What is the significance of the chipset? 75. What is the function of the BIOS? 76. What is the function of the CMOS chip? 77. Explain the booting process when the computer is switched on. 78. What is POST? Section 2.10.2–2.10.7 79. List five ports and interfaces available on the backside of the computer to connect the devices. 80. What devices are attached to—(a) Serial Port, (b) Parallel Port, (c) USB Port, (d) Firewire, (e) RJ45 connector, (f) VGA connector, (g) Audio plugs (Line-In, Line-Out and microphone), (h) PS/2 Port, and (h) SCSI Port. 81. List five expansion slots available in the computer. 82. What devices are attached to—(a) ISA slots, (b) PCI slot, (c) AGP slot, (d) PCI Express slot, and (e) PC Card. 83. What is the purpose of the Ribbon cables? 84. Two types of memory chips _____ and _____ are used in desktop computers. 85. List any three storage devices that are attached to the computer. Extra Questions 86. Give full form of the following abbreviations 1. IC 2. MIPS 3. EISA 4. PCI 5. USB 6. AGP 7. BIPS 8. SIMM 9. DIMM 10. GHz 11. MHz 12. PCB 13. BIOS 14. CMOS 15. POST 16. ISA 17. ROM 18. ACC 19. IR 20. PC 21. MAR 22. MBR 23. DR 24. RISC  25. CISC 26. ATX 27. SATA 87. Write short notes on— 1. Working of computer 2. Central processing unit 3. Registers 4. Cache memory 5. RAM 6. Control unit 7. ALU 8. Instruction format 9. Instruction set 10. Instruction Cycle 11. Microprocessor 12. System bus 13. Expansion bus 14. Performance of computer 15. System clock 16. Motherboard 17. BIOS 18. CMOS chip 19. Ports and interfaces in computer 20. Expansion slots 21. Main components in a computer case 88. Give differences between the following— 1. Registers and cache memory 2. Cache memory and RAM 3. RISC and CISC 4. System bus and expansion bus 5. Data bus, address bus and control bus 3 COMPUTER MEMORY Contents  Memory representation   Memory hierarchy—Internal memory (registers, cache memory, primary memory), secondary memory (magnetic disk, optical disk, magnetic tape)  Registers, cache memory  Primary memory—Random access memory, read only memory  RAM—DRAM, SRAM, memory modules— DIMM, SIMM  ROM—PROM, EPROM, EEPROM, flash memory  Secondary memory  Access types of storage devices—Sequential access devices, direct access devices  Magnetic tape—Working of magnetic tape, features of magnetic tape  Magnetic disk—Working of magnetic disk, features of magnetic disk, finding data on magnetic disk o Floppy disk o Hard disk o Zip disk  Optical disk—CD-ROM, DVD-ROM, recordable optical disk o CD-R o CD-RW o DVD-R  Magneto-optical disk  Using the computer memory Why this chapter From the moment you switch on a computer till you switch it off, computer uses its primary memory. When you request for the processing of data and instructions, the processor uses its registers, cache memory, primary memory and secondary memory. As a computer user, you need to be aware of the memory present in a computer. This chapter describes the different kind of memories, their use and the interaction between them. 3.1 INTRODUCTION The computer’s memory stores data, instructions required during the processing of data, and output results. Storage may be required for a limited period of time, instantly, or, for an extended period of time. Different types of memories, each having its own unique features, are available for use in a computer. The cache memory, registers, and RAM are fast memories and store the data and instructions temporarily during the processing of data and instructions. The secondary memory like magnetic disks and optical disks have large storage capacities and store the data and instructions permanently, but are slow memory devices. The memories are organized in the computer in a manner to achieve high levels of performance at the minimum cost. In this chapter, we discuss different types of memories, their characteristics and their use in the computer. 3.2 MEMORY REPRESENTATION The computer memory stores different kinds of data like input data, output data, intermediate results, etc., and the instructions. Binary digit or bit is the basic unit of memory. A bit is a single binary digit, i.e., 0 or 1. A bit is the smallest unit of representation of data in a computer. However,