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# Basics of Computer

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computer is a calculating machine which is used to perform arithmetic and logical operation at a high speed. …

computer is a calculating machine which is used to perform arithmetic and logical operation at a high speed.
A computer is an electronic device that can accept, store and process information to produce the required result.
Therefore, we can define computer as a device that transforms data. Data can be
anything like marks obtained by you in various subjects. It can also be name, age, sex,
weight, height, etc. of all the students in your class or income, savings, investments, etc.,
of a country.
Computer is a device that can solve any mathematical operation and it
operates on information or data.
Computer can be defined in terms of its functions. It can (i) accept data
(ii) store data, (iii) process data as desired, (iv) retrieve the stored data
as and when required and (v) print the result in desired format.

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• 1. BASIC CONCEPTS OF COMPUTER 1-1 1.1. INTRODUCTION The word “computer” comes from the word “compute” which means to calculate. So computer is a calculating machine which is used to perform arithmetic and logical operation at a high speed. A computer is an electronic device that can accept, store and process information to produce the required result. Therefore, we can define computer as a device that transforms data. Data can be anything like marks obtained by you in various subjects. It can also be name, age, sex, weight, height, etc. of all the students in your class or income, savings, investments, etc., of a country. Computer is a device that can solve any mathematical operation and it operates on information or data. Computer can be defined in terms of its functions. It can (i) accept data (ii) store data, (iii) process data as desired, (iv) retrieve the stored data as and when required and (v) print the result in desired format. LEARNING OBJECTIVES At the end of this chapter you will be able to understand : Definition of Computer Features and Generation of Computer Classification of Computers Organization of Computer Bus Architecture Instruction Set Memory and Storage System L L L
• 2. 1-2 BASIC CONCEPTS OF COMPUTER The number of applications of a computer has increased day by day. The speed and accuracy of calculation is also increasing day by day. You can use of computers in our day to day life. Reservation of tickets in air lines and railways, payment of telephone and electricity bills, deposits and withdrawals of money from banks, business data processing, medical diagnosis, weather forecasting, etc. are some of the areas where computer has become very useful. 1.1.1. Features of Computer The computer has following features : 1. Speed. Computer can works with a high speed. Computer can perform millions (1,000,000) of instructions and even more per second. Therefore, we determine the speed of computer in terms of microsecond or in nano second. So you can imagine how fast your computer work. 2. Accuracy. The accuracy of a computer very high a computer performs each and every calculation with the same accuracy. Errors can occur in a computer but these are mainly due to human or technological weaknesses. If the instructions are not correct or the data is wrong, the result coming out of the computer would be wrong. 3. Storage.Acomputer can store large amounts of information in its memory. Computers have very large storage capacity. The information can be stored as long as desired by the user and can be recalled when required. Even after several years. The information recalled would be as on the day when it was fed to the computer. 4. Diligence. A computer is free from tiredness and lack of concentration. As compare to human being, it can work many hours without creating any error. 5. Versatility. Computers can perform a wide range of jobs with speed, accuracy and diligence. Computers are used in every fields such as accounting, generating pay-slips, keeping track of the records of students, play games, listening music, watching movies during the recreation hours. 1.1.2. Limitation of Computer The computer provides many facilities and benefits to the user. But it has some limitations, which are given below : 1. Intellegence (No I.Q.). The computer has no intelligency. It has to be told what to do and in what will be the sequence. Only user can determine what tasks a computer will perform. 2. Feelings. The computer has no feelings because it is a machine. Computer cannot make judgments of their own. Its judgment is based on the instructions given by the user to them in the form of programs. 3. Can not remove error itself. The computer cannot remove errors itself. If this type of situation arises, computers will produce wrong results. They do not have potential to work out alternate solutions.
• 3. BASIC CONCEPTS OF COMPUTER 1-3 4. Can not work without human intervantion. Computer can not perform any task on its own. It can not take independent decision. It requires human instruction to take a decision or what to do. 1.1.3. Generations of Computer The word “Generation” for computers indicates a steps in technology. The computer has following generation. 1. First Generations. The computers produced between 1942-1955 are called the first generation computers. These machines were based on “vacuum tube”. IBM 650 was the most popular first generation computer. Advantages (a) Vacuum tubes were the only electronic components available during those days. (b) Vacuum tube technology made possible the advent of electronic digital computers. (c) These computers were the fastest calculating devices of their time. (d) They could perform computations in milliseconds. Disadvantages (a) Too heavy in size. (b) Unreliable. (c) Thousand of vacuum tubes were used. They produced large amount of heat. (d) Air conditioning required. (e) Possibility to frequent hardware failures. (f) Constant maintenance required. (g) Not portable. (h) Manual assembly of individual component into functioning required. (i) Commercial production was difficult and costly. (j) Limited commercial use. 2. Second Generation. In second-generation computers advanced technology can be used. Vacuum tubes were replaced by “transistors”. These components were smaller in size, easier to manufacture, less power consuming and cheaper. IBM 700 was one of the computers of second generation. Advantages (a) Smaller in size as compared to first generation computers. (b) More reliable. (c) Less heat generated.
• 4. 1-4 BASIC CONCEPTS OF COMPUTER (d) These computers were able to reduce computational times from milliseconds to microseconds. (e) Less possibility to hardware failures. (f) Better portability. (g) Wider commercial use. Disadvantages (a) Air conditioning still required. (b) Frequent maintenance required. (c) Manual assembly of individual components into a functioning unit was required. (d) Commercial production was difficult and costly. 3. Third Generation. The third generation computers were based on integrated circuits. The “integrated circuits” (IC) based on the small, medium and large scale integration (LCI) technology replaced transistors. The third generation computers are much cheaper and more reliable than the second generation computers. Advantages (a) Smaller in size as compared to previous generation computers. (b) Even more reliable than second-generation computers. (c) Even lower heat generated than second generation computers. (d) Able to reduce computational times from microseconds to nanoseconds. (e) Maintenance cost is low because hardware failures are rare. (f) Easily portable. (g) General purpose. Widely used for various commercial applications all over the world. (h) Less power requirements than previous generation computers. (i) Commercial production was easier and cheaper. Disadvantages (a) Air conditioning required in many cases. (b) Highly sophisticated technology required for the manufacture of IC chips. 4. Fourth Generation. The fourth generation computers used “VLSI” (very large scale integration) technology. This technology led to the development of microprocessors, where on entire CPU circuitry is placed on a single chip. This generation used a newer electronic technology, which enabled them to be even smaller and faster than third generations. Computers like IBM PCs, Apple Macintosh etc. are the computer of this generation.
• 5. BASIC CONCEPTS OF COMPUTER 1-5 Advantages (a) Low cost machine. (b) High speed. (c) Large memory. (d) Small size. (e) Less power consumption. (f) Floppy disk is used as storage device. Semi conductor internal memory. (g) Improve in software (spread sheet). (h) Hardware failure is negligible. (i) Heat generated is negligible. (j) Cheapest among all generations. Disadvantages (a) Highly sophisticated technology required for the manufacture of ISI chip. 5. Fifth Generation. Scientists are now at work on the fifth generation computers. They aim to bring us machines with genuine “intelligence”. 1.2. CLASSIFICATION OF COMPUTER There are different types of computers are available in the market. Though each computer we can do different type of work. All types of computers are available in different sizes. They have different capabilities as working mechanism like, calculation work, weather forecasting, and statistical analysis for business management etc. That is why computer is divided/classified according the following : 1. Classification based on application/computational method. 2. Classification based on purpose. 3. Classification based on size and capability. 1.2.1. Classification based on application. Computers are divided in three parts on the basis of application. (i) Analog Computer (ii) Digital Computer (iii) Hybrid Computer (i) Analog Computer. This type of computer is worked on quantity like in petrol pump, weather forecasting, temperature etc (as shown in Fig.1.1). Analog computers process data input in a continuous form. Data is such as voltage, resistance or temperature is represented in the computer as a continuous, unbroken flow of information. Inside this computer analog signals are used for working. They are worked in the form of wave.
• 6. 1-6 BASIC CONCEPTS OF COMPUTER Fig.1.1. Analog Computer. Advantages (a) Analog computers carried out measurement by a few single purpose devices. So they are offers low cost. Disadvantages (a) The main disadvantage of an analog computer is the accuracy factor that why the result of analog computers is not accurate. (b) Analog computer has limited storage capacity. (c) Analog computers are not suitable for processing business data. (ii) Digital Computers. It is a general computer works on 1 and 0 as shown in Fig.1.2. It gives accurate result because this computer uses digital signals for working. A digital computer can count, and accept numbers and letters through various input devices. The
• 7. BASIC CONCEPTS OF COMPUTER 1-7 input devices convert the data into electronic pulses and perform arithmetical operations on numbers in discrete form. Fig.1.2. Digital Computer. Advantages (a) Digital computers give result any desired level of accuracy. It can be achieved by considering as many places of decimal as are necessary. (b) Digital computers are most suitable for business application. Disadvantages (a) The main disadvantage is high cost of digital computer. (b) Digital computers have complexity in programming. (iii) Hybrid Computers. This computer is a combination of analog and digital computer. For this computer both analog and digital signals worked. It can converts the analog signal to digital signal and digital signal to analog signal. Modem is an example of hybrid system. 1.2.2. Classification based on purpose. There are two types of computer in this category. (i) General purpose computer (ii) Special purpose computer
• 8. 1-8 BASIC CONCEPTS OF COMPUTER (i) General purpose computer. General-purpose computer is a normal computer that is used everywhere. This type of computer can do programming, calculation, accounting work or painting work. This computer is generally used in homes, schools and colleges. Digital computer is an example of general-purpose computer. (ii) Special purpose computer. This computer is designed according to special tasks like for weather forecasting, research or to make a film in photo studio. 1.2.3. Classification based on size and capability. In this category computer is divided into four parts : (i) Micro computer. (ii) Mini computer. (iii) Mainframe computer. (iv) Super computer. (i) Micro Computer. Microcomputers were first available for widespread use in the 1970’s when it becomes possible to put CPU into a small silicon chip. It is very smallest computer. It is portable we can move it easily from one place to another (as shown in Fig.1.3). Its storing capacity is very less and speed is also slow as compared to mini, mainframe and super computer. Its data transfer rate is very slow. We can do normal calculations in this computer. Fig.1.3. Micro Computer. These computers are used in schools, colleges, homes and offices. Example are Desktop, Palmtop, Notebook and workstation. (ii) Mini Computer. Minicomputer is bigger than microcomputer as shown in Fig.1.4. They are larger in size and have large amount of storage capacity. But less as compared
• 9. BASIC CONCEPTS OF COMPUTER 1-9 to mainframe and super computers. These computers are used in offices, small companies. Fig.1.4. Mini Computer. They are used for processing data and analyzing results of experiments. Its data transfer rate is high. We can connect many computers. Some examples are PDP 11/42, Vax 11, and IBM series. (iii) Mainframe Computer. Mainframe computers are more powerful and costly as compare to minicomputer as shown in Fig. 1.5. They are special computers big in size and capable to handle all kinds of scientific and business applications. They can process several million instructions per second. Its storing capacity is very high and data transfer rate is too high. It has large on-line secondary storage capacity. Fig.1.5. Mainframe Computer.
• 10. 1-10 BASIC CONCEPTS OF COMPUTER We can connect more than 500 computers through this computer. They are used in WAN. They are used in big companies and factories like BSNL, NTPC and SBI. For Ex: ES/9000 family of IBM. (iv) Super Computer. Super computer is the largest and fastest computer. They are used in fields like science and defense services. These computers are used for designing and launching missiles weather forecasting, bio-medical research aircraft design and automobile design. Its processing speed ranges from 10,000 million instructions per second (MIPS) to 1.2 billion instructions per/sec. They can support 10,000 terminals at a time. They have huge numbers of storage and other devices connected to them. Example of Supercomputer is CRAY-1, CRAY-2, and CRAY-3. India have a Super Computer PARAM-10000. 1.2.4. Types of PC (Personal Computer) Personal computer is divided into following types: 1. Desktop 2. Laptop 3. Notebook 4. Palmtop 5. Workstation 1. Desktop. Desktop is a microcomputer that can be put over table and can be transfer form one place to another. It is used in home, schools, college etc. Its storage capacity is very high as compare to other personal computer. Desktop storage capacity is in the form of GB. We can use floppy disk, CD, DVD or pen drive in personal computer. 2. Laptop. Laptop is a portable PC that can be easily portable anywhere as shown in Fig. 1.6. That is a briefcase type computer that works with electricity as well as with battery. Its working is similar to desktop computer but more costly then desktop. Fig.1.6. Laptop PC.
• 11. BASIC CONCEPTS OF COMPUTER 1-11 Its storage capacity is in Giga bytes (GB).CD, DVD and pen drive can also used in Laptop. In this computer LCD (Liquid Crystal display) is used instead of CRT (Cathode ray tube) picture tube. 3. Notebook. Note book is another type of personal computer as shown in Fig. 1.7. This is very small in size that can be keeping inside of pocket. But in this computer we cannot work like a desktop and Laptop computer. It can be run with both electricity and battery. Fig.1.7. Notebook PC. They have the size of a notebook. There weight is in approx. 3 to 4 kg. 4. Palmtop. Palmtop is a small computer that is like the size of a pocket calculator as shown in Fig.1.8. It is not powerful as computer to above personal computers. They support only a few applications. Fig.1.8. Palmtop PC. Through this PC calculation can be done and can store information also. Through this we can access internet. Its screen is smaller than notebook. Example : HP 95 LX.
• 12. 1-12 BASIC CONCEPTS OF COMPUTER 5. Workstations. In workstation computers desktop computer is used but more than one desktop computer can be connected with each other. The configuration of workstation system is very high, like processor speed, memory storage, and size of RAM similar to server. The speed of connected computer also depends upon number of workstation. 1.3. COMPUTER ORGANISATION A computer performs basically five major operations: 1. Input. This is the process of entering data and programs into the computer system. The input takes data from the user to the computer in an organized manner for processing. 2. Storage. The process of saving data and instructions permanently is known as storage. 3. Processing. The task of performing arithmetic and logical operations on data that converts them to useful information, called processing. 4. Control. The manner how instructions are executed and the above operations are performed is called controlling. 5. Output. This is the process of producing results from the data for getting useful information. In order to carry out the operations mentioned in the above section the computer organized the task between its various functional units.Ablock diagram of the basic organization is shown in Fig. 1.9. Fig.1.9. Computer Organization. 1. Input Unit. Input unit is a device which provides communication between user and computer. Input of any form is first converted into binary electronic signals (0 and 1), which can be understood by CPU. This process is called digitizing. The input unit takes data from us to the computer in an organized manner for processing. In short, the following functions are performed by the inputs unit : (a) The input units convert our enter data into binary patterns for the machine and transfer it to the memory. L
• 13. BASIC CONCEPTS OF COMPUTER 1-13 (b) The memory stores the input information that may be data or program. It also stores the data processed in the arithmetic unit. 2. Output unit. The output coming from the CPU and make it understandable by human beings, i.e. graphical, alphanumeric in human language, audio visual. Output unit of computer display the result. Output units perform following function : (a) Display the result on visual display unit such as monitor. (b) In printed form by printers. (c) In graphic form by plotters. (d) In the form of sound by speaker. (e) Through other output devices such as projector or LCD. 3. Storage unit. Data has to be fed into the system before the actual processing starts. It is because the processing speed of CPU is very fast. The data has to be provided to CPU with the same speed. That is why the data is first stored in the storage unit for faster access and processing. Thus storage unit of the computer system is designed to do the above functionality. It provides space for storing data and instructions. L Storage unit provides space for storing data and instructions in computer. The storage unit performs the following major functions: (a) All data and instructions are stored here before and after processing. (b) Intermediate results of processing are also stored here. 4. Central processing Unit. The CPU is also called the brain of the computer. This is because an execution of any task is controlled by the CPU. CPU takes information from the input unit and processes it according to instructions. A central processing unit (CPU) controls the execution of programs and performs the calculations. A CPU performs following tasks: (a) Manipulating the data like word processing, letter. (b) Writing, sorting, editing, makes catalog of data. (c) Converting data of one form into another. (d) Communicating data to far off distances. (e) Storing the data temporarily and retrieving it as and when required. (f) CPU does everything in the form of binary language (0 and 1). 5. Arithmetical and Logical Unit (ALU). ALU is designed to perform the four basic arithmetic operations like add, subtract, multiply, divide and logical operations or comparisons such as less than, equal to or greater than. It can do complex calculations with fast speed. L L
• 14. 1-14 BASIC CONCEPTS OF COMPUTER L ALU is used to perform arithmetical and logical operations. The functions of this unit are : (a) ALU takes data from memory unit and returns information to memory unit. (b) ALUusedanumberofregistersandaccumulatorsforshorttermstorageofcharacters while doing calculations or computations 6. Control Unit (CU). The control unit worked like the supervisor seeing that things are done in proper fashion. Control unit determines the sequence in which computer programs and instructions are executed. This unit obtains instruction from the programs stored in main memory, interprets the instructions and issues signals that cause help other units of the system to execute them. 1.4. REGISTER The basic function performed by a computer is the execution of a program. The program which is to be executed, is a set of instructions, which is stored in memory. The central processing unit (CPU) executes the instructions of the program to complete a task. L Registers are temporary storage units within the CPU. The major responsibility of the register is instruction execution with the CPU. The instruction execution takes place in the CPU registers. Let us, discuss few typical registers that are commonly available in some of the machines. These registers are: 1. Memory Address Register (MAR). It specifies the address of memory location from which data or instruction is to be accessed for read operation or to which the data is to be stored for write operation. 2. Memory Buffer Register (MBR). This register contains the data to be written in the memory for write operation or it receives the data from the memory for read operation. 3. Program Counter (PC). It keeps track of the instruction, which is to be executed next, after the execution of an on-going instruction. 4. Instruction Register (IR). Here the instructions are loaded before their execution. The simplest model of instruction processing can be a two-step process. The CPU reads (fetches) instructions (codes) from the memory one at a time, and executes or performs the operation specified by this instruction. The instruction fetch is carried out for all the instructions. Instruction fetch involves reading of an instruction from a memory location to the CPU. The execution of this instruction may involve several operations depending L
• 15. BASIC CONCEPTS OF COMPUTER 1-15 on the nature of the instruction. 1.5. BUS ARCHITECTURE In computer architecture, a bus is collection of control lines, address lines and data lines that transfers data between computer components inside a computer. A set of parallel conductors which allow the flow of instructions and data between devices. The bus consists of three main parts: 1. Control lines. These allow the CPU to control which operations, the devices attached should perform, For Example read or write. 2. Address lines.Allows the CPU to reference certain (Memory) locations within the device. 3. Data lines. The meaningful data which is to be sent or retrieved from a device is placed on to these lines. Bus Architecture. In Bus-based computers, the processors, memory and I/O devices are connected to a backbone called bus that acts as a “superhighway” for data or instructions to move among processors, memory and I/O devices as shown in Fig. 1.10. Fig. 1.10. A bus architecture. L
• 16. 1-16 BASIC CONCEPTS OF COMPUTER 1.6. INSTRUCTION SET An instruction set made up of a combination of an operation code and way of specifying an operand by its location or address in memory. Some operation codes deal with more than one operand the locations of these operands may be specified using any of the many addressing schemes. For example of a one- address instruction is add x are as following : ❍ Add contents of address x. ❍ To contents of accumulator. ❍ Sum remains in accumulator. An example of a three-address instruction to add x, y, z are as following : ❍ Add contents of address x. ❍ To contents of address y. ❍ Sum is placed in location z. 1.7. MEMORY Memory is a location to store something. Computer memory is used to store data, information and programs.Acomputer works like the human brain, computer can not do work without it. Computer memory is used to store instructions and data to perform an operation. Computer uses two types of storage or memory: 1. Primary memory. 2. Secondary memory. Primary memory is accessible directly by the CPU. RAM is an example of primary memory. Secondary memory such as floppy disks, magnetic disk located outside the computer. L L
• 17. BASIC CONCEPTS OF COMPUTER 1-17 1. Primary memory. Primary memory is known as “main memory” or “internal memory” of computer. The primary memory of a computer stores the data provided by the user and the instruction provided by the programs. It is a portion of CPU where current data or program resides for execution in computer. It stores the results also, which can be there after transferred to output unit. Primary memory is a part of computer where current data or program resides for execution. The primary memory is placed on the motherboard in the form of chips. There are only two basic types of primary memory : (a) RAM (random access memory). (b) ROM (read-only memory). (a) RAM (Radom Access Memory). RAM is also the “main memory” that is used to store programs and data that the computer needs when executing programs. The RAM is volatile and loses this information once the power is turned off (as shown in Fig.1.11). Fig.1.11. RAM. There are two general types of chips used to build the RAM memory in today’s computers: (i) SRAM (static random access memory). (ii) DRAM (dynamic random access memory). (i) SRAM (Static random access memory). SRAM is faster and much more expensive than DRAM which can store many bits per chip, uses less power, and generates less heat as compact DRAM. (ii) Dynamic RAM (Dynamic random access memory). Dynamic RAM is work L
• 18. 1-18 BASIC CONCEPTS OF COMPUTER with tiny capacitors that leak electricity. DRAM requires a recharge every few milliseconds to maintain its data. Static RAM technology, in contrast, holds its contents as long as power is available. (b) ROM (Read-only memory). ROM is a primary memory that stores information necessary to operate the system, such as the program necessary to boot the computer as shown in Fig.1.12. ROM is non-volatile and always contains its data. Fig.1.12. Read Only Memory. There are different types of ROM : PROM, EPROM, EEPROM, and flash memory. (i) PROM (programmable read-only memory). PROM is those in which the user can insert the contents of choice only once. It can only be read and never written, means recorded information can not be changed. PROM is non-volatile storage. (ii) EPROM (erasable PROM). In EPROM information can be erased and the chip can be programmed to record different information. Eraser is achieved by exposing the chip to ultraviolet light. EPROM is also known as UPROM (ultraviolet PROM) or EAPROM (electricity Alterable). (iii) EEPROM (electrically erasable PROM). EEPROM removes many of the disadvantages of EPROM no special tools are required for erasure and you can erase only portions of the chip or one byte at a time. This is done by applying electronic beams on an electric field. (iv) Flash memory. it is essentially EEPROM with the added benefit that data can be written or erased in blocks, with removing the one byte at a time limitation. This makes flash memory faster than EEPROM. 2. Secondary memory. This memory is designed for user. We can store information in permanent form. These devices hold the huge amount of information, which may be transferred for use during processing as and when required. (a) It has much larger capacity but it is not as fast. (b) Computer takes slightly more time to retrieve data from secondary storage. (c) Secondary memory is ultimate in size and much cheaper than main memory. The next section 1.8 discuss secondary memory in brief.
• 19. BASIC CONCEPTS OF COMPUTER 1-19 Secondary memory store huge amount of data and information in parament form that may be transferred for use when required. 1.8. SECONDARY MEMORY AND STORAGE SYSTEMS Secondary memory is a LSO called “auxiliary” memory or “secondary storage”. In this type of memory the cost per bit of storage is low. However, the operating speed is slower than the primary storage. Huge volume of data are stored on permanent basis and transferred to the primary storage when required. Most widely used secondary storage devices are magnetic tapes, hard disk, floppy disk, CD or DVD. 1.8.1. Magnetic Tape. Magnetic tapes are used where large volume of data is stored for a longer time as (shown in Fig.1.13). The cost of storing data in tapes is inexpensive. Tapes consist of magnetic materials that store data permanently. It can be 12.5mm to 25mm wide plastic film-type and 500meter to 1200meter long which is coated with magnetic material. The deck is connected to the central processor. It is similar to cassette tape recorder. Fig.1.13.Magnetic Tape. Advantages (a) Compact. The maximum capacity of such a tape is 180 million characters. Thus data are stored much more compactly on tape. (b) Economical. The cost of storing characters is very less as compared to other storage devices. (c) Fast. Copying of data is easier and fast. (d) Long term Storage and Re-usability. Magnetic tapes can be used for long term storage and a tape can be used repeatedly with out loss of data. 1.8.2. Hard Disk. Hard disk is an expensive storage device. Because this device contains disc as well as drive. Its storing capacity is highest. This device works on a direct L
• 20. 1-20 BASIC CONCEPTS OF COMPUTER storage method. It is a sealed aluminum box. Hard disk is a sealed unit containing a number of platters in a stack. Electromagnetic read/write heads are positioned above and below each platter. As the platters spin, the drive heads move in toward the center surface and out toward the edge. In this way, the drive heads can reach the entire surface of each platter. On a hard disk, data is stored in thin bands. Adrive head can read or write a circular ring or band called a track. There can be more than a thousand tracks on a 3.5-inch hard disk. Sections of each track are called sectors. A sector is the smallest physical storage unit on a disk which store 512 bytes in size. The Fig.1.14 below shows the structure of a hard disk. A cylinder is formed while all drive heads are in the same position on the disk. The tracks stacked on top of each other form a cylinder. The system disk controller reads this data to place the drive heads in the correct sector position. Fig.1.14. Structure of Hard Disk. 1.8.3. Floppy Disk. Floppy Disk is similar to magnetic disk discussed above. It is a direct storage device.Asmall flexible disk used as storage medium for small computer is known as floppy disk as shown in Fig.1.15. It is used to store information. Its storing capacity is 1.44 MB. This device is coated with magnetic particles. It is one of the most common storages media that is usually used to move data from one location to another. The disadvantage of a floppy disk is that, it is prone to damage by heat and dust.
• 21. BASIC CONCEPTS OF COMPUTER 1-21 Fig.1.15. Floppy Disk. Today floppies are available in two sizes. (1) 3.5 inch floppy (2) 5.25 inch floppy 1. 3.5 inch floppy. It is a very small size floppy. This disk is covered with hard plastic. It is dust free. Its storing capacity is 1.44 MB. It has write protected notch. 2. 5.25 Inch floppy. Its size is greater than 3.5 floppy. Its body cover is very soft. The capacity of a 5.25-inch floppy is 1.2 mega bytes it is easily damaged by dust as dust can insert in it. It has write-protected notch. If button is down. We can read information only. We can not change information of it and not write or copy any information, virus also cannot be shifted. If button is up. We can do all write, copy and virus can be shifted also. 1.8.4. Optical Disk. These devices store more than floppy but less than hard disk. They are much reliable as compare to floppy disk. It is the necessity to store large volume of data that has led to the development of optical disk storage medium. Optical disks can be divided into the following categories: 1. Compact disk read only memory (CD-ROM). CD-ROM (as shown in Fig. 1.16) disks are made of reflective metals. CD-ROM is written during the process of manufacturing by high power laser beam. Here the storage density is very high, storage cost is very low and access time is relatively fast. Each disk can hold over 600 MB of data or more than it. As the CD-ROM can be read only, we cannot write or make changes into the data contained in it.
• 22. 1-22 BASIC CONCEPTS OF COMPUTER Fig.1.16. Compact Disk. 2. Write once read many (WORM).AWORM allows the user to write data permanently on to the disk. Once the data is written, it can never be erased without physically damaging the disk. Here data can be recorded from keyboard, video scanner, OCR equipment and other devices. The advantage of WORM is that, it can store vast amount of data, amounting in gigabytes. Any document in a WORM can be accessed very fast, say less than 30 seconds. 3. Erasable optical disk. These are optical disks where data can be written, erased and re-written. This also applies a laser beam to write and re-write the data. These disks may be used as alternatives to traditional disks. Erasable optical disks are based on a technology known as magnetic optical (MO). To write a data bit on to the erasable optical disk the MO drive's laser beam heats a tiny, preciously defined point on the disk's surface and magnetizes it. 4. Digital video disk (DVD). DVD stands for Digital Versatile Disk or Digital Video Disk. It is possible to have 4.7 GB. GB ordinary data or mix DVD-Video and data on a recordable DVD that can be played by most computer DVD-ROMs. 5. Zip drive. Zip drive is a storage device similar to floppy. But its size is greater than floppy. Its body cover is harder than floppy. Its storing capacity is approx. 100 MB. Zip drive can be fixed in CPU and zip floppy can be inserting only in it. Zip drives are gaining popularity in the market. Zip disks are used for lacking up hard disks and transferring large files. It is used to create zip disks. POINTS TO REMEMBER (i) The word personal computer (PC) is actually used for IBM-compatible PC. (ii) Modem is abbreviation of modulation and demodulator. (iii) Modem converts the digital signals from the computer to analog signal and vice- versa.
• 23. BASIC CONCEPTS OF COMPUTER 1-23 (iv) RAM is volatile memory. (v) ROM is non-volatile memory. 1 Byte = 8 bits (vi) 1 KB (Kilo-Byte) = 1024 Bytes 1 MB (Mega Byte) = 1024 KB = 1024 × 1024 Bytes 1 GB (Gega Bytes) = 1024 MB = 1024 × 1024 × 1024 Bytes. (vii) Units of microprocessor speed is Mega Hertz (MHz). (viii) Hybrid computer is a combination of analog and digital computer. (ix) India have a super computer named PARAM-10000. (x) CPU is also called the brain of the computer. KEY TERMS ❍Analog computer ❍ Digital computer ❍ Hybrid computer ❍ Mainframe computer ❍ Mini-computer ❍ Super computer ❍ Instruction set ❍ Bus architecture ❍ Control unit ❍Arithmetic logic unit ❍ Storage unit ❍ Central processes unit ❍ Primary memory ❍ Secondary memory ❍ Magnetic tape ❍ Hard disk ❍ Floppy disk ❍ Optical disk ❍ Read only memory ❍ Random access memory ❍ Compack-disk read only memory ❍ Digital video disk MULTIPLE CHOICE QUESTIONS 1. The first generation computer is based on………… (a) Vacuum tube (b) IC (c) Both (a) and (b) (d) None of these 2. Which of the following is not personnel computer (a) Desktop PC (b) Laptop (c) Workstation (d) Mainframe 3. Which of the following is not portable PC (a) Laptop (b) Palmtop (c) Notebook (d) None of these 4. The Computer works on 0’s and 1’s format is called (a) Analog (b) Digital (c) Hybrid (d) All of the above
• 24. 1-24 BASIC CONCEPTS OF COMPUTER 5. The CPU stands for (a) Central processing unit (b) Central programming unit (c) Control processing unit (d) None of the above 6. Which of the following is not part of CPU (a) Primary memory (b) ALU (c) CU (d) Input unit 7. The memory Cell smallest unit is (a) 1 bit (b) 1 byte (c) Both (a) and (b) (d) None of the above 8. The RAM is types of (a) SRAM (b) DRAM (c) Both (a) and (b) (d) None of the 9. The PROM is stand for (a) Programmable read only memory (b) Proper read only memory (c) Permanent read only memory (d) Program read only memory 10. The HDD is type (a) Fixed (b) Movable (c) Both (a) and (b) (d) All of the above ANSWERS 1. (a) 2. (d) 3. (d) 4. (b) 5. (a) 6. (d) 7. (a) 8. (c) 9. (a) 10. (c) UNSOLVED QUESTIONS 1. What is computer and discuss about features of computer and also the limitation ? 2. Draw a block diagram of computer. Explain the function of each of the blocks. 3. Explain the importance of a bus in the computer system. 4. Explain in detail the different categories of RAM. 5. What is ROM ? Explain the different types of ROM. 6. Describe the classification of storage systems with the helop of a diagram. 7. What are magnetic storage systems ? Describe magnetic tape and magnetic disks with their relative advantages and disadvantages. 8. What is register ? Explain different type of register. 9. What is the difference between primary and secondary memory ? 10. What is the difference between hard disk and floppy disk ? ❍ ❍ ❍