Book 9 Revised by Krishna K. Shrestha Oasis Radiant Computer Science Oasis Publication (P) Ltd. Anamnagar, Kathmandu Phone :0977-01-4313205 Approved by the Government of Nepal, Ministry of Education, Science and Technology, Curriculum Development Centre (CDC), Sanothimi Bhaktapur
Oasis Radiant Computer Science Class 9 Revised by Krishna K. Shrestha Layout Design: Zeeta Computer Service Pvt. Ltd. Ghantagrar, Kathmandu Publisher: Oasis Publication (P) Ltd. Anamnagar, Kathmandu Nepal Tel: 977-01-4313205 www.oasispublication.com.np Printed in Nepal © Publisher First edition : 2017 Second edition : 2020 Revised edition : 2022 This book belongs to... Name : Mr./Miss ...................................................... Class : ................ Section. ............ Roll No....... School : ...................................................................... ....................................................................................
Acknowledgement We are in the 21st century. This is the age of Information and Communication Technology (ICT). ICT has become an integral part of our daily life. It facilities the work of business people, academicians, students and professionals in banking and other sectors. Computer education has become a fundamental right of children. Children need the knowledge of computer, from the basic to advanced level, to cope with the changes happening now and unfolding in the future. The Curriculum Development Centre (CDC) of Nepal government has prescribed syllabi and course outlines for computer education in schools from primary to higher secondary level. Students, however, are deprived of quality computer education due to the lack of quality course books and limited access to the computer system in schools. To address this issue, I have developed a complete series of computer books, under the banner of Oasis Radiant Computer Science, from grade I to grade XII. I have devoted a lot of time and effort in the research and development of this book. It provides a comprehensive and balanced coverage of the CDC syllabus. This series was possible due to the comprehensive support of my colleagues, family members, students and teachers. I would like to acknowledge all who have directly or indirectly encouraged me to prepare this book in the series. Specially, my thanks go to the students and teachers of different schools for their regular interactions and inspirations I have had in preparing this book. In the same way, my thanks go to my parents Tek Nath and Chisa Maya Adhikary, family members Lachhima Adhikary, Jagan Adhikary, Sarashwati Adhikary and lovely kids Samridhi, Sampada, Prasamsha, Ballavi, Ragavi, Suyash and Suyasha Adhikary for their valuable contribution to prepare this book. I must also give due thanks to OASIS PUBLICATION family for their innovative help to prepare and publish this book. Finally, all the suggestions and comments are acknowledged. Thanking all, Author
Syllabus Area Contents Tentative No. of Classes Th Pr 1. Computer Fundamental (1.1) Introduction (Importance and modern application areas) (1.2) Types of Computers (Digital, Analog & Hybrid) (1.3) Computer System (Basic Architecture) (i) Input (ii) Process (iii) Output (iv) Storage (1.4) Computer Hardware (a) Motherboard (b) Microprocessor (c) Memory (i) Primary (RAM, ROM, Cache Memory) (ii) Secondary - Magnetic Storage Device (Tape, Hard Disk, Flash Memory) - Optical Storage Device (CD-ROM, CD-RW, DVD ROM, Blue Ray Disk etc) (iii) Units of memory measurement (BIT, Nibble, Byte, KB, MB, GB, TB, PB) (d) Input Devices - Keyboard, Mouse, Scanner, Track ball, Touch pad, Joystick, Scanner, Bar Code Reader, Digital Camera, Microphone,Graphic Digitizer, Touch Screen, QR Code Scanner (e) Output Device - Monitor, Printer & its type, Speaker, Graphic Plotter (1.5) Computer Software (1.5.1) Types of Computer Software (a) System Software (i) Operating System and its functions Types of OS - Single User - Multi User GUI Environments - Introduction to GUI Environments (Desktop) - Concepts of Icon, Windows dialogue box, GUI Controls - Mouse pointer and its activities - File and Folder Management (ii) Language Processor (b) Application Software (c) Utility Software (1.5.2) Introduction Open Source Software (1.5.3) An introduction to desktop & web apps 33
2. Working with Graphics (2.1) Different Graphics Format (2.2) Graphics for Web (2.3) Image size, resolution (2.4) Graphics Editing - Changing the size and format of image - Text and selection tool - Cropping images 7 17 3. Internet and Web Technology (3.1) Internet Technology And introduction to - web browser, search engine, upload, download, webserver, URL, home page, web page, website, DNS - IOT (Internet of Things) - Cloud Computing (3.2) HTML (3.2.1)Creating, opening and formatting HTML Document - <HTML>, <HEAD>, <TITLE>, <BODY> (BGCOL- OR), <P> (ALIGN), <FONT> (SIZE, COLOR & FACE), <H1> <H6> (ALIGN), <B>, <I>, <CEN- - TER>, <U>, <SUB>, <SUP>, <BR>, <HR> - (3.2.2) Setting marquee - <MARQUEE> (BEHAVIOR, BG- COLOR) (3.2.3) Creating Links - <A> (HREF) (3.2.4) Inserting Images - -<IMG> (SRC, WIDTH, HEIGHT) (3.2.5) Working with table - -<TABLE> (BORDER, BGCOLOR), <TD>, <TR> (3.2.6) Working with forms - Different form Elements (3.3) CSS (Cascading Style Sheets) Introduction to CSS, CSS syntax, CSS Measuring Units, CSS: Colors, Backgrounds, Fonts, Text, Images, Links, borders, margins 20 34 4. Computer Programming (4.1) General Concept (a) Programing & programer (b) Programming language (c) Translator (Compilers and Interpreters) (d) Algorithm and Flow chant (4.2) Programming in QBASIC (4.2.1) Introduction (a) Features of QBASIC programming QBASIC interface (Screen, menus, shortcut commands) (4.2.2) Data types 27 34
(a) Numeric (Integer, Long integer, single precision, double precision) (b) Varaiables and rules for naming variables (c) Constants (Literal and symbolic) (d) Variable Declaration (Implicit and Explicit) (i) Using type declaration characters (%, &, !, # and $) (ii) Using DIM AS statement (4.2.3) Operators, operands & expenssions (a) Operators and their precedence (i) Arithmetic operators (+,-,*,/,\,MOD,^) (ii) Relational operators (=,>,>,>=,<=,<>) (iii) Logical operators (AND, OR, NOT) (iv) String Operators (+) (v) Assignment operators (=) (b) Expression (i) Arithmetic expression (ii) Logical (Boolean expression (iii) String expression (4.2.4) Program Statements (use and syntax) (a) Declaration statement (CONST, DIM, REM) (b) Assignment statement (LET, SWAP) (c) Input/Output statement - CLS, INPUT, LINE INPUT, READ ... DATA, INPUT$, INKEY$, PRINT, LPRINT, PRINT USING, LPRINT USING, TAB, SPC, LOCATE, DATE$, TIME$ (4.2.5) Program flow and control structures (a) Sequence Structure (b) Selection Structure (IF, SELECT statement) (c) Loop Structure (FOR, WHILE, DO WHILE statements) (4.2.6) Library Functions String manipulation functions : (ASC, CHR$, LEFT$, RIGHT$, MID$, LTRIM$, RTRIM$, VAL, STR$, SPACE$, STRING$, LCASE$, UCASE$, DATE$, TIME$) Mathematical Calculation Functions (ABS, COS, SIN, TAN, GQR, SGN, INT) (ABS, COS, SIN, TAN, SQR, SGN, INT) (4.2.7) Arrays (Declaring and Using) (a) Array Variables (b) Array elements and subscripts (c) One dimensional array (Searching, Sorting) (d) Two dimensional array (general concept) 85 85
Contents Chapter Lesson Page No. 1 Introduction to Computer 11 2. Types of Computer 22 3. Computer System 31 4. Computer Hardware 39 5 Computer Software 59 6. Working with Graphics 75 7. Internet and Web Technology 102 8. HTML 112 9. Cascading Style Sheet (CSS) 135 10. General Concept of Programming 160 11. Programming in QBASIC 176 12. Program Statements 191 13. Arrays 222 Full Forms 243 Word Meaning 247
Oasis Radiant Computer Science, Book 9 10
Approved by Curriculum Development Centre 11 Oasis Radiant Computer Science, Book 9 Chapter 1 Introduction to Computer ffl Introduction to computer. ffl Characteristics of computer. ffl Limitations of computer. ffl Modern application areas of Computers. THIS CHAPTER COVERS :
Oasis Radiant Computer Science, Book 9 12 Approved by Curriculum Development Centre Introduction to 1 Computer Chapter Introduction A computer is a machine that helps us enter data, store them and process the data to give a meaningful result as output. In other words, a computer is an electronic calculating device that takes data according to the instructions as input, stores them, processes the data according to the instructions and produces the desired result as output. The term was derived from the Latin word ‘Computare’ which means to calculate. Now, we use computers to process alphanumeric as well as other types of data. A computer not only performs addition, subtraction, multiplication and division but also reads data, stores them and processes them to produce the results. So, we can say that the functions of a computer are broader than just computing. Input Process Storage Output Characteristics of Computer A computer has some features or capabilities that make it a special device. Some of the major characteristics of a computer are discussed below: a. Speed The speed of a computer is very high. It can process millions of instructions per second (MIPS) without any mistake. The speed of a computer is usually
Approved by Curriculum Development Centre 13 Oasis Radiant Computer Science, Book 9 given in terms of the following time units. Units of Time Parts of seconds Meaning 1 Millisecond (1ms) 1/1000 or 10-3 A thousandth of a second 1 Microsecond (1us) 1/1000000 or 10-6 A millionth of a second 1 Nanosecond (1ns) 1/1000000000 or 10-9 A thousand millionth of a second 1 Picosecond (1 ps) 1/1000000000000 or 10-12 A million millionth of a second 1 Femtosecond (fs) 1/1000000000000000 or 10-15 A trillionth of a second 1 Attosecond (as) 1/1000000000000000000 or 10-18 A thousand trillionth of a second 1 Zeptosecond (1zs) 1/1000000000000000000000 or 10-21 A million trillionth of a second 1 Yoctosecond 1/1000000000000000000000000 or 10-24 A trillion trillionth of a second The speed of a computer is also measured in terms of instructions per second like KIPS (Kilo Instructions Per Second ) or MIPS (Millions of Instructions Per Second). b. Storage Computers can store a large amount of data. They have main memory and secondary memory. The storage capacity of a computer is unlimited due to the capacities of secondary storage devices. They can store and retrieve a huge volume of data in an easy, fast and efficient manner. The storage capacity of primary as well as secondary memories of a computer is measured in terms of bits, Bytes, Kilobytes, Megabytes, Gigabytes, Terabytes and so on. The following table gives the basic measurement units of computer memory. 1 or 0 1 bit 4 bits 1 Nibble 8 bits 1 Byte
Oasis Radiant Computer Science, Book 9 14 Approved by Curriculum Development Centre 1024 Bytes 1 Kilobyte (KB) 1024 KB 1 Megabyte (MB) 1024MB 1 Gigabyte (GB) 1024 GB 1Terabyte (TB) 1024TB 1 Petabyte (PB) 1024 PB 1 Exabyte (EB) 1024 EB 1 Zettabyte (ZB) 1024 ZB 1 Yottabyte (YB) c. Accuracy The accuracy of a computer is 100% in spite of its high speed. If we find errors, they are due to human factors, not because of the computer. The errors may be in coding the program, program logic and data entry. The errors of computer program are called bugs. The process of removing errors from a program is called debugging. If a wrong or false input is given, the output is also wrong. So, a computer is also called as GIGO (Garbage In Garbage Out) machine. d. Versatility Computers are versatile machines. That means, they can perform varieties of jobs ranging from simple to complex and sophisticated calculations. In other words, we can say that computers are capable to do any type of task. The application areas of computers are very wide. So, they can be used in education, business, commerce, industry, medicine, engineering and many other sectors. e. Diligence Computers are diligent machines. Human beings suffer from weaknesses like tiredness, lack of concentration and laziness. So, human beings can’t perform the same task over and over again with the same speed, accuracy and efficiency. Being a machine, a computer does not get tired or bored. It doesn’t lose concentration and feel lazy. This feature of a computer is called diligence.
Approved by Curriculum Development Centre 15 Oasis Radiant Computer Science, Book 9 f. Automatic A computer is an automatic machine. Once the process has been initiated, it is capable of functioning automatically till completion. It doesn’t require instructions again and again once the data is provided. Limitations of a Computer a. Computers don’t have common sense; IQ of computer is zero. b. Computers don’t have thinking capacity. c. Computers cannot run without electricity. d. They can’t decide on their own. Adverse Effects or Disadvantages of Computer a. Computers can affect our eyes if we sit in front of their screen for a long time. b. Computers can reduce our creativity if we depend too much upon it. c. Computers are machines and machines can break any time. d. Due to the change in technology daily, people believe that they can lose their jobs if they do not upgrade themselves. Application of Computer It is obvious that the computers are changing our daily life. People are using computers for performing a range of tasks, from small to complex in nature. You can use your computer system for different applications by changing the software packages. In education sector, computers are especially used in the teaching and learning process, In business, computers are used for promoting products and services and performing calculations. In the communication sector, it is especially used for reliable transmission of messages. In medicine, computers are especially used for the diagnosis. Some of the common applications of computer are : i) Business application ii) Scientific research iii) Education iv) Entertainment v) Banks vi) Communication vii) Engineering viii) Medicine ix) Office and so on
Oasis Radiant Computer Science, Book 9 16 Approved by Curriculum Development Centre i) Business Application In business, companies use computers to grow their business as fast as possible with quick analysis of their previous project on the computer screen (according to the data supplied inside) and deciding what to do next without any delay. From individuals to multinational companies, all are using computer for business purposes like keeping records of accounts, stocks, prices and items as well as for promoting their business all over the world. ii) Scientific Research Scientific research has also been one of the application areas of computer since its first use in research. From that time to now, the speed and accuracy of computer have enabled scientific analysis to be carried out fast. Computer controlled robots must be used in all those areas where there is a danger to human beings such as in nuclear research and deep sea investigation. iii) Education Education sector is also one of the application areas of computer due to which we can easily understand the subject matter and teachers/students can exchange their knowledge through different tools such as projectors, laptops and online classes. Now-adays, there are thousands of websites available over internet that are ready to deliver education for free in almost every subject. You can choose whether you want to learn online or offline. In online learning, you can open any website to read your desired topic while in offline learning you can learn through videos, PDFs, and photos, for example, and all these documents can be downloaded through internet.
Approved by Curriculum Development Centre 17 Oasis Radiant Computer Science, Book 9 iv) Entertainment and game playing Most people are using computer for entertainment purposes such as watching movies and videos or tuning in to songs and animations. Computers can be used to create these things in an attractive manner so that users love to have fun with them. Computers are also used to play different online and offline games. v) Banks Banks are the places where computers are used all the while or we can say that banks are the major users of computers. For example, ATM (automated teller machine) is used where we are free to either deposit money in our bank or withdraw our cash from it. In banks, all information such as account holder’s details, deposits, withdrawal and interest are managed by computers. Banks are also using computer network to interconnect all of its branches so that their users feel always free to deposit their money in any branch of the same bank. vi) Communication Using your computer system for the purpose of communication gives you a lot of benefits. For example, if you use email to send message or anything to your friends or any of your contacts, then you don’t have to use pen and paper to write and take that paper to the post office waiting then for the postman to deliver that letter after a few days. If you want to send any urgent information, postal delays will be a trouble. Therefore, using email, you can also save your time and cost to deliver any information very fast. You only need a computer and internet
Oasis Radiant Computer Science, Book 9 18 Approved by Curriculum Development Centre connectivity. Now-a-days, people are using chat message, email and voicemail for communication purposes. vii) Engineering Purposes Computers are also being used in engineering, that is, to design any machine without actually making it through CAD (Computer Aided Design) software and once the design is accepted, and then using CAM (Computer Aided Manufacturing). CAD and CAM help companies produce a large number of products very fast. Architects are also using computers to draw and design anything from individual houses to big buildings and apartments. There are a lot more uses of computer for engineering purposes than mentioned above. viii) Medicines Related Computers play an important role in medical field also. For example, in an ICU (Intensive Care Unit) in a hospital, the computer keeps track of each and everything going inside the patient’s body such as blood pressure and heartbeat. Keeping records of patients and medicines also becomes easy through the use of computer. Computers also play an important role to perform CT (Computed Tomography) scan and X-Ray of patients to give the scanned object of specified area of patient’s body in the form of graphics like images. ix) Office Computers are used in office for keeping different records as well as for the processing of different things. Due to computers in office, the paper text files are replaced by digital files.
Approved by Curriculum Development Centre 19 Oasis Radiant Computer Science, Book 9 Computers have helped to improve the efficiency and accuracy of office workers by providing different software and communication functions to help them execute their tasks. Computers are a part of nearly every office, with most workplaces now unable to function without the use of computers. Points to remember • A computer is an electronic data processing device. • A computer has become a special device due to its storage capability. • The speed of a computer is measured in millions of instructions per second. • The storage capacity of a computer is measured in bits, bytes, kilobytes, megabytes and so on. • Computers don’t have self-decision making capability. • Computers can create different types of health problems. • Computers are capable of doing simple to complex calculations. • Computers never feel tired or bored or lose concentration. • We can use computer systems or different applications by changing the software packages. • In medical sector, computers are used for diagnosis. • Banks are the places where computers are in use all the while. • Computers are now a part of every office. Exercises 1. Fill in the blanks. a. …………….is a programmable machine. b. The word computer was derived from the Latin word………… which means to calculate. c. 1 microsecond is a ……………of a second. d. 1 GB is equal to ……………….MB.
Oasis Radiant Computer Science, Book 9 20 Approved by Curriculum Development Centre e. Computers can affect our ……………if we sit in front of the screen for a long time. f. Computer are 100% ............ g. Different types machines are designed by ……………. software. 2. State whether the following statements are True or False. a. A computer is an electronic programmable machine. b. A computer performs arithmetical and logical operations. c. Computers can make their own decisions when needed. d. Computer is not a diligent device. e. Computers are capable of doing many tasks. f. Computers are not automatic, they need humans to operate. g. Risky jobs are done by robots. 3. Write technical terms for the following. a. The result produced by a computer. b. The error in a computer program. c. The collection of 1024 bytes. d. One million millionth of a second. e. Process of removing errors or bugs from computer. f. The term for the statement: if wrong instruction is given result is also wrong. g. A machine which gives 24 hours services. h. A trillion trillionth of a second. 4. Write the full form of : i. CAD ii. ZB iii. ICU iv. PDF v GIGO vi. MIPS 5. Answer the following questions. a. Define computer. b. List all the characteristics of a computer. c. Define the terms, bug and debugging. d. Make a table of time units to measure the speed of computer. e. Make a table of measurement units of computer data. f. Why is computer called a diligent device? g. Write the limitations of a computer. h. Write some of the adverse effects or disadvantages of computer. i. What are CAD and CAM?
Approved by Curriculum Development Centre 21 Oasis Radiant Computer Science, Book 9 6. Select the correct answer from the given alternatives: a. How many steps does Information Processing Cycle has? i. Four ii. Two iii. Three iv. Five b. When input is wrong, then output will also be wrong, it is termed as i. GIGO ii. IPM iii. Bug iv. Debug c. Repeated working capability of computer is known as, i. Accuracy ii. Versatility iii. Diligence iv. Storage d. The speed of computer is measured in terms of i. Megabyte ii. Megahertz iii. Megapixel iv. Megasecond e. How many bytes make 1 kilobyte? i. 1020 ii. 2048 iii. 1024 iv. 1000 f. Which of the following is one billionth of a second? i. millisecond ii. microsecond iii. nanosecond iv. picosecond 7. Match the following: Column A Column B GIGO Nanosecond One Megabyte No feeling Education One billionth of a second Limitation of computer Application of computer 1024 KB Accuracy
Oasis Radiant Computer Science, Book 9 22 Approved by Curriculum Development Centre Chapter 2 Type of Computer ffl Analog, Digital and Hybrid computers. ffl Mainframe, Mini and Micro computers. ffl IBM PC, IBM compatibles and Apple/Macintosh computers. ffl XT, AT and PS/2 computers. THIS CHAPTER COVERS :
Approved by Curriculum Development Centre 23 Oasis Radiant Computer Science, Book 9 All around the world there are different types of computers used by different people at different places. These computers can be classified into different categories on the following basis: 1. On the basis of Work 2. On the basis of Size 3. On the basis of Brand 4. On the basis of Model The chart below shows the classification of computer. Classification of Computer On the Basis of Work On the Basis of Work On the Basis of Brand On the Basis of Model Analog Computer Digital Computer Hybrid Computer Mainframes Computer Mini Computer Micro Computer IBM PC IBM Compatible Apple/Macintosh AT XT PS/2 1. On the basis of Work On the basis of their working principle, computers are of three types. They are: a. Analog Computers b. Digital Computers c. Hybrid Computers Type of Computer 2 Chapter
Oasis Radiant Computer Science, Book 9 24 Approved by Curriculum Development Centre a. Analog Computer An analog computer is the one that measures physical quantities such as temperature, pressure, voltage and current. Analog computers are especially suited for the solution of complex equations. Firstly, all operations in an analog computer are performed in parallel. Secondly, data are represented in an analog computer as voltages. Analog computers are specific-purpose computers. Speedometer in cars and motor bikes are example of analog devices. Some examples of analog computers are Seismograph and Plesley. Also the devices which measure the size of kidney in hospitals are analog computers. Hetauda Cement factory is also using an analog computer named Process Control. Among all the computers in Nepal, the share of analog computers is less than 1%. b. Digital Computer A computer that stores data in terms of digits (number) is known as digital computer. Digital computers are general purpose computers. In digital computers, letter, words and whole texts are represented digitally. Digital computers don’t measure the distance, quantities or pressure. These computers are mostly used in the preparation of reports, results, tabulation and graphic representations. They are mostly used in mathematics, engineering and statistics. on% of computers in Nepal are digital computers. c. Hybrid Computer Hybrid computer is a combination of analog and digital computers. This integration is obtained by digital to analog and analog to digital converter. A hybrid computer may use or produce analog data or digital data. It accepts
Approved by Curriculum Development Centre 25 Oasis Radiant Computer Science, Book 9 a continuously varying input which is then converted into a set of discrete values for digital processing. These computers are generally used in ICU’s of hospitals to measure the heartbeat of the patient. Hybrid machines are generally used in big industries, scientific research institutions, airplanes and others areas. Both the jet planes of Nepal-Karnali and Gandaki are facilitated with hybrid computers and therefore, these planes are called computerised jet planes. Some hybrid computers are: Flight Management Computer (FMC), Engine Indicator and Crew Alert System (ELCAS). Differences between Analog and Digital computers. Analog Computer Digital Computer 1. It measures continuous data 1. It measures discontinuous or discrete data. 2. It measures physical quantities such as temperature, pressure and values like 1, voltage and current. 2. It measures digital values like 0 3. Some examples are Seismograph, Plesley, Process Control. 3. Some examples are personal computer or micro computers like desktop, laptop and palmtop. 2. On the basis of Size Computers are of various sizes. According to their size, they are mainly divided into three categories. They are: a. Mainframe Computers b. Mini Computers c. Micro Computers a. Mainframe Computer They are the largest, fastest and perhaps one of the most expensive computers. Super computers are more powerful and computes have strong capacity and high processing speed. These computers are multi-terminal systems as they are concerned with more than hundred terminals (monitors). These computers can handle big processing tasks such as population census, agro-census, industries, SLC results and Provident Fund of Government employees. IBM 1401 was the first
Oasis Radiant Computer Science, Book 9 26 Approved by Curriculum Development Centre mainframe computer brought in Nepal for the population census of 2028 BS ICL 2950/10 was another mainframe computer which was used for the 2038 BS census. These computers are still present in National Computer Centre (NCC). b. Mini Computer These computers are smaller than Mainframe computers in size. They are more powerful and expensive than micro computers. These are also multi-terminal computers, as they are connected with more than 50 terminals at a time. National Computer Centre, Nepal Telecommunication, Nepal Rastra Bank, Agricultural Bank, Police Headquarters and Electricity authorities are using mini computers. Some example of mini computers are Data General, Primer and Neck. c. Micro Computer These computers contain microprocessor as the main processor. They are also called Home computers or personal computers. They are mostly used at homes and offices. Nowadays, the capabilities and speed of micro computers have increased. A small office is enough for setting up the micro computers. They are smaller than mini computers and are available in various sizes such as desktop, laptop and palmtop. i. Laptop: We call them laptop because they can easily be kept on the lap of the user. They are portable computers which can be carried anywhere easily just like a briefcase. People involved in tasks that require them to move from one place to another like to have laptops as they are easy to carry and handy to use. ii. Palmtop: These computers are smaller than the laptop and can be adjusted within the palm of the user.
Approved by Curriculum Development Centre 27 Oasis Radiant Computer Science, Book 9 iii. Desktop: These computers can easily be placed on a desk. So, we call it a desktop computer. These computers are specially used as personal computers or PCs. Generally, we see these computers in schools. 3. On the basis of Brand On the basis of brand, there are three types of computers. They are: a. IBM PC b. IBM Compatibles c. Apple / Macintosh a. IBM PC IBM PC stands for International Business Machine Personal Computer, made by IBM company, established by Dr. Herman Hollerith in 1923 AD. It is the largest computer manufacturing company in the world even today. All the computers manufactured by this company are IBM PCs. These computers are reliable and durable. They have high processing capacity. They are also known as branded computers as all the parts of these computers are manufactured by IBM company itself. b. IBM Compatibles Compatible means something that can be adjusted to work together. So, all the computers that are not manufactured by IBM Company but are the same in appearance and manufacturing like IBM PCs are known as IBM Compatible computers. It is also called assembled PC as parts of different companies are assembled to make the computer. They are less powerful, less expensive and less
Oasis Radiant Computer Science, Book 9 28 Approved by Curriculum Development Centre durable than IBM branded PCs. They are the most popular computers of the world today. They are also known as duplicates of IBM. c. Apple/Macintosh Apple corporation is also one of the largest computer manufacturing companies of the USA. All the computers that are manufactured by Apple Corporation, USA are known as Apple/Macintosh computers. In these computers, monitor and system unit are attached with each other. These computers have their own hardware and software. They are mostly used in design works. 4. On the basis of Model On the basis of model, there are three types of computers. They are: a. XT (eXtended Technology). b. AT (Advanced Technology). c. PA/2 (Personal System-2). a. XT : The computers having 8086 and microprocessors are XT computers. XT stands for eXtended Technology. They have the processing speed of 4.77 MHz. b. AT : The computers having 80286, 80386, 80486 microprocessors are AT computers. AT stands for Advanced Technology. They have higher capacity than XT. In these computers, apart from AT processor, math co-processors are also used for additional calculations. c. PS/2 : The new model computers manufactured by IBM after 1990 are known as PS/2 (Personal system/2) computers. These computers are used for general purpose computation. They can run word processing, spreadsheet, database management and accounting packages and so no. The processing speed of these computers is higher than that of AT computers.
Approved by Curriculum Development Centre 29 Oasis Radiant Computer Science, Book 9 Points to remember • On the basis of size, computers are categorised as Mainframe, Mini and Micro computers. • On the basis of brand, computers are categorised as IBM PC, IBM compatibles and Apple/Macintosh computers. • On the basis of work, computers are categorised as Analog, Digital and Hybrid computers. • On the basis of model, computers are categorised as XT, AT and PS/2 computers. Exercises 1. Fill in the blanks: a. The……………………...computers are also called personal computers. b. Mainframe computers are the………………and most ………computers. c. The IBM Compatibles are also called as ……………….IBM. d. IBM PC uses microprocessor of ………………………………company. e. …………………………...computers have their own hardware and software. f. Laptop and palmtop are examples of ……………………..computers. g. Mainframe are ……………………………terminal system. h. Minicomputers are ………………………..than mainframe computers. 2. State whether the following statements are True or False. a. Motorola processor is used in IBM computers. b. Micro computer contains microprocessor as the main processor. c. Mini computers are bigger than Mainframe computers. d. IBM PC and IBM compatibles are the same computers. e. Only 10 terminals can be attached to a mainframe computer. f. Analog computers represent data in the form of physical quantity g. The mini computers are bigger than mainframe computers. h. Digital computers work in analog signal. i. Microcomputers are used in your school and homes.
Oasis Radiant Computer Science, Book 9 30 Approved by Curriculum Development Centre 3. Answer the following questions. a. List the main categories of computers. b. What are different types of computers according to size? c. Differentiate between mainframe and mini computers. d. Name the different types of micro computers. e. What is the difference between IBM PC and IBM Compatibles? f. Why do we call IBM Compatibles as duplicates IBM PCs? g. Differentiate between analog and digital computers. h. Give any two examples of hybrid computers. 4. Write the technical terms for the following. a. Computer that measures physical quantities. b. Computer that stores data in terms of digits. c. First computer brought in Nepal. d. Computers having 80286, 80368, 80486 microprocessor. e. Computer, also known as branded computer. f. Computer easily carried like a briefcase. 5. Match the following. Group “A” Group “B” a. Analog computer i. manufactured after 1990 b. Laptop computer ii. branded computer c. IBM PC iii. contains microprocessor d. PS/2 computer iv. measure physical quantities v. Portable computers
Approved by Curriculum Development Centre 31 Oasis Radiant Computer Science, Book 9 Chapter 3 Computer System ffl Discussion of the concept of computer system ffl Discussion of the architecture of computer ffl Discussion of the input and output devices ffl Description of the memory system of computer THIS CHAPTER COVERS :
Oasis Radiant Computer Science, Book 9 32 Approved by Curriculum Development Centre Computer System 3 Chapter Introduction Computer is an electronic device that processes data to give meaningful information. It is also known as data processor. It accepts transaction data and processes to convert them into meaningful form and then deliver the output to the user. Basically computer system has three components input, processing and output. Computer system has four basic elements: hardware, software, human ware and firmware. Hardware Hardware is the physical structure of the computer. Popular parts of hardware are: • Input hardware such as keyboard and mouse. • Output hardware such as monitor and printer. • Processing hardware such as Central Processing Unit and Memory System. Software Software is the group of programmes and application environment used in computer system. Popular software systems are: • Operating system software such as Windows and MSDOS. • Application programmes such as MS Word, Excel, and Access.
Approved by Curriculum Development Centre 33 Oasis Radiant Computer Science, Book 9 Humanware Humanware is the interaction between computer system and the user. It describes the instructions and user’s skill to operate the computer. This is possible due to the common working platform like operating system of computer. Firmware Firmware is a micro programme stored on the Read Only Memory (ROM) of computer -- for example, programmes stored on BIOS (Basic Input Output System) to configure the computer system. Architecture of Computer Architecture of computer is the internal structure of computer that shows the basic parts of the computer system. It is also called basic logical block diagram of computer. It explains the input, processing, output and storage units of the computer system.
Oasis Radiant Computer Science, Book 9 34 Approved by Curriculum Development Centre Central Processing Unit Computer architecture describes the computer system into three sections as given in the above figure. Different devices are attached on input, output and the processing sections of the computer for capturing input from the user, process it and give the result to the user. Input and output devices attached to the computer system are called computer peripherals. Input Unit It is the data entry unit of the computer. It accepts data and instructions from the user and converts them into machine code and deliver to the processing section of the computer. Popular input devices are: Keyboard, Mouse, Microphone and Scanner. Processing Unit It is the main part of the computer so sometimes it is called heart or brain of the computer system. The unit that performs logical and arithmetical processing is processing unit. It is popular as Central Processing Unit (CPU). It has three sections, MU (Memory Unit), ALU (Arithmetic Logic Unit) and CU (Control Unit) Central Processing Unit (CPU) As given in the figure alongside, CPU is the central processing unit of computer. It process data according to our instructions. Processing is a procedure that transforms raw data into meaningful information. It consists of three sections: a) Arithmetic Logic Unit (ALU) b) Control Unit (CU) c) Memory Unit (MU) The Arithmetic Logic Unit (ALU) It consists of a number of accumulators or registers in its constructions. It is the main computing part of CPU. It performs various arithmetic and logical operations of the programme. Operations are addition, subtraction, multiplication and division. The logical instructions performed are logical AND operation, logical OR operation and logical NOT
Approved by Curriculum Development Centre 35 Oasis Radiant Computer Science, Book 9 operation. It uses different operators such as +,- , * , ^ , / , IF, OR and AND. Control Unit It is a unit which controls the entire system of computer. This unit directs all operations inside the computer. It will make a proper sequence to direct the data and instructions from the memory to ALU (Arithmetic Logic Unit) for precise operations performed by ALU (Arithmetic Logic Unit). The control unit of the CPU (Central Processing Unit) consists of a small, high speed memory used to store temporary results and certain control information. It controls signals to various parts of the computer. The main functions of control unit are given below: • It performs the data processing operations with the aid of programme prepared by the users and sends control signals to various parts of the computer system. • It gives commands to transfer data from the input device to the memory to arithmetic logic unit. • It also transfers the results from ALU to the memory and then to the output devices. Output Unit The unit that gives the result to the user is output unit. The result from the processing unit is called output. Output section converts the result from machine code to user language and delivers it to the user. Popular output devices are: Monitor, Speakers, and Printers. Memory Unit It is a part of CPU where all the given instructions, data and the results are stored during the processing period. By using the unique address we can identify the locations of memory. There are different types of memory, among them the popular are RAM (Random Access Memory) and ROM (Read Only Memory). Memory refers to the electronic holding place for instructions and data where the computer’s microprocessors can reach quickly. Computer needs memory to store the data and process them. We can represent the memory using different units like: Bits = 0 and 1 8 Bits = 1 Byte (One Character) 1024 Byte = 1 Kilo Byte (KB)
Oasis Radiant Computer Science, Book 9 36 Approved by Curriculum Development Centre 1024 KB = 1 Mega Byte (MB) 1024 MB = 1 GB (Giga Byte) 1024 GB = 1 TB (Tera Byte) Points to remember • A computer system is the combination of different computer hardware and software that work together to achieve the common objectives. • A computer system performs mainly five basic operations in order to convert raw data into meaningful information. • Input devices accept data and instructions from the user. • The CPU is the brain of any computer system. • The speed of a microprocessor is measured in terms of MagaHertz (MHz) or GigaHertz (GHz). • ALU is designed to perform the four basic arithmetic operations-add, subtract, multiply, divide and logical comparisons such as less than, greater than or equal to. • Control unit manages and coordinates the entire computer system. • The memory unit or the primary memory is a part of the CPU where the instructions and data to be processed are stored temporarily. • Output unit supplies information and result of computation to the outside world.
Approved by Curriculum Development Centre 37 Oasis Radiant Computer Science, Book 9 Exercises 1. Write whether the following statements are True or False. a. Inputting, storing, processing, outputting and controlling are the five main basic operations of a computer system. b. Input unit accepts data and instructions from the user and convert them into human understandable from. c. The CPU contains arithmetic logic unit, control unit and memory unit. d. All the calculations and decisions are made in the ALU. e. Actual processing on the data is performed by the control unit. 2. Fill in the blanks. a. A………………..is the set of hardware and software which work together to achieve the common objectives. b. The speed of microprocessor is measured in terms of ……………….. or…………… c. The …………………..is a section of CPU where the actual execution of the instructions takes place during the processing. d. ………………………..and ………………………...are the example of primary memory or main memory. e. ……………………unit supplies the final results to the outside world. 3. Write the full form of the following abbreviations. CPU, ALU, MHz , RAM, ROM 4. Match the following. Group “A” Group “B” a. Inputting i. Saving data and instruction b. Storing ii. Producing useful information c. Processing iii. Entering data and instructions d. Outputting iv. Performing arithmetic and logical operations
Oasis Radiant Computer Science, Book 9 38 Approved by Curriculum Development Centre 5. Write the technical terms for the following. a. Directing the manner and sequence in which the operations are performed. b. The place where the actual execution of the instructions takes place during the processing. c. The unit that acts as a central nervous system. d. The unit of a computer that supplies information to the outside world. e. It acts as a central nervous system. f. It converts the result into human understandable from. 6. Answer the following questions. a. Define computer system. Name the five basic operations of a computer system. b. What are the functions performed by the input unit? c. Name any four input devices. d. What is the role of ALU in the computer system? e. What is memory unit? Why does a computer need primary memory? f. What is an output device? Name any four output devices. 7. Class Activity a. Identify the parts of a computer system. 8. Project Work a. Compare the computer system with TV and calculator in terms of input, processing, output and storage.
Approved by Curriculum Development Centre 39 Oasis Radiant Computer Science, Book 9 Chapter 4 Computer Hardware ffl Discussion of the concept of computer system ffl Discussion of the architecture of computer ffl Discussion of the input and output devices ffl Description of the memory system of computer THIS CHAPTER COVERS :
Oasis Radiant Computer Science, Book 9 40 Approved by Curriculum Development Centre Computer Hardware 4 Chapter Introduction Physical parts of computer which can be seen and touched are known as hardware. All the peripheral devices attached to the computer are hardware: keyboard, mouse, monitor, system unit, CD, floppies, scanners and printer. All the power cables, data cables, connectors and chips are also hardware. Let’s discuss the main circuit board of a computer which is also known as printed circuit board or motherboard. Motherboard The motherboard is the main component inside the system case. It holds many of the crucial electronic components of the system such as the Central Processing Unit (CPU) and memory and provides connectors for other peripherals. CPU is also known as the brain of the computer which is present in motherboard. Since CPU is the brain of the computer, motherboard is the central nervous system of the computer. Components of a Motherboard Central Processing Unit (CPU) A central processing unit (CPU) is the hardware within a computer that carries out the instructions of a computer programme by preforming the basic arithmetical, logical and input/output operations of the system. Bus A computer bus (often simply called Bus) is an electronic pathway. Its role is to transfer data, signal or power from one part to another part of computer. Different types of buses are data bus, address bus and control bus.
Approved by Curriculum Development Centre 41 Oasis Radiant Computer Science, Book 9 Expansion Slot An expansion slot is a socket on the motherboard that is used to insert an expansion card (or circuit board) which allows us to connect additional devices to a computer such as video, sound, advanced graphics, Ethernet or memory. Cooling Fan Cooling fan is a fan present inside the system unit which keeps the computer cool by throwing the hot air outside and letting cool air into the system unit from outside. CMOS Battery CMOS batteries help in running the computer’s internal clock and help in changing the data of a computer regularly even if the computer is switched off. This is the reason why a computer regularly changes its data and time even when the computer is switched off. Lithium CR2032 batteries which last from 2 to 10 years depending upon the type of motherboard
Oasis Radiant Computer Science, Book 9 42 Approved by Curriculum Development Centre are best for computers. Higher temperatures and longer power off times shortens the cell life. ROM BIOS The ROM chip contains a small programme known as firmware which holds the booting instruction of a computer. It helps in starting up the computer. Parts of Motherboard Parallel Port A parallel port is a type of interface found on computers (personal and others) for connecting peripherals. In computing, a parallel port is a parallel communication physical interface. It is also known as a printer port. The parallel port interface was originally known as the LPT (Line Print Terminal) port. Serial Port As the name suggests, it allows the transfer of data in a serial way. In a serial port, only one line/wire is used to transfer data. It is used for slow speed peripherals such as keyboard, mouse and modem. Serial ports are faster than parallel ports. PS/2 Port PS/2 port was developed by IBM. It is also called mouse port. It is used to connect a computer mouse or keyboard. It is a round connector with 6 pins. A colour code is used to distinguish between the two ports. The keyboard port is purple and the mouse port is green. Universal Serial Bus (USB) Port USB was designed to standardise the connection of computer peripherals (including keyboards, pointing devices, digital cameras, printers, portable media players, disk drives and network adapters) to personal computers,
Approved by Curriculum Development Centre 43 Oasis Radiant Computer Science, Book 9 both to communicate and supply electric power. It has become a port for PDAs and video games. USB has effectively replaced a variety of earlier interfaces such as serial and parallel ports as well as separate power chargers for portable devices. Fire Wire Port FireWire interface is also known as IEEE 1394 port. IEEE stands for ‘Institute of Electrical and Electronic Engineers’. It is a serial bus interface especially created for high speed audio and video transmission. Microprocessor Microprocessor is a single chip with millions of components like transistors. It performs all the operations of the computer’s processor. It is made of VLSI(Very Large Scale Integrated Circuit) and ULSI(Ultra Large Scale Integrated Circuit). Intel Corporation of USA developed the first microprocessor named ‘Intel 4004’ in 1971 AD. The main responsibilities of microprocessor are : a. To control and coordinate all the operations and other components of the computer system. b. To carry out processing. c. To give commands to all the other components of the computer system. d. To control the sequence of operation in the computer system. e. To interpret the data, instruction and information in the computer system. Memory It is a part of CPU where all the given instructions, data and results are stored during the processing period. By using the unique address we can identify the locations of memory. There are different types of memory. Among them, the popular ones are RAM (Random Access Memory) and ROM (Read Only Memory). Memory refers to the electronic holding place for instructions and data where the computer’s microprocessors can reach quickly. Computer needs memory to store
Oasis Radiant Computer Science, Book 9 44 Approved by Curriculum Development Centre the data and process them. We can represent the memory by using different units like: Bits = 0 and 1 8 Bits = 1 Byte (One Character) 1024 Byte = 1 Kilo Byte (KB) 1024 KB = 1 Mega Byte (MB) 1024 MB = 1 GB (Giga Byte) 1024 GB = 1 TB (Tera Byte) Types of Memory Basically we have two types of memory used on a computer system. These are the primary memory which is known as the main memory or internal memory or simply memory and the secondary memory which is known as auxiliary memory or backup storage or external memory. Besides these two memories, we have internal processor memories such as cache memory, register and virtual memory. Primary Memory The CPU contains the basic instructions needed to operate the computer, but it doesn’t have the capability to store entire programmes or data permanently. The CPU contains registers, but these are small areas that can hold only a few bytes of data at a time. However, the CPU needs to have millions of bytes of space to hold programmes and the data being manipulated. This area is called memory. Physically, memory consists of chips either on the motherboard or on a small circuit board attached to the motherboard. There are two types of memory: 1. Permanent/Non-volatile Memory: Memory that stores data permanently. Example: ROM. 2. Temporary/Volatile Memory: Memory that will become empty after turning off the computer system. Example: RAM.
Approved by Curriculum Development Centre 45 Oasis Radiant Computer Science, Book 9 RAM (Random Access Memory) It is temporary memory. After the switch-off of the computer, its contents will be erased. RAM which is volatile in nature. It is a high speed memory that holds programmes and data only when in use. It requires constant supply of power. It is also called Read/Write Memory. The most important factor affecting the speed and power of a computer is the amount of RAM it has. The more RAM in a computer, the more it can do. The measuring unit of memory is byte, which is the amount of memory required to store a single character. RAM has the ability to access each byte of data directly, so it is named Random Access Memory. There are two types of RAM: SRAM (Static RAM) and DRAM (Dynamic RAM). ROM (Read Only Memory) These are non-volatile chips always holding the same data. Data in them can’t be changed, that is, the contents in ROM cannot be written or erased by the user; these are “hard-wired” or done only once by the manufacturer, hence they are called Read Only Memory or sometimes called permanent memory. Generally, ROM contains system programmes for handling the operating system. There are different types of ROM: Programmable Read Only Memory (PROM), Erasable Programmable Read Only Memory (EPROM) and Electrically Erasable Programmable Read Only Memory (EEPROM). Difference between permanent and temporary memory RAM and ROM both are primary forms of memory. S.N. RAM ROM 1. It stands for Random Access Memory. It is also called read/ write or volatile memory, because its contents can be emptied when refresh command is executed or computer is shut down. It stands for Read Only Memory. It is called- dead store, field store, permanent store and non-volatile memory.
Oasis Radiant Computer Science, Book 9 46 Approved by Curriculum Development Centre 2. Its content is lost if the power is off. It retains contents even if the power is off. 3. RAM is divided into two categories: Static RAM and Dynamic RAM. ROM is divided into PROM, EPROM and EEPROM. 4. Costly Cheap Secondary Memory These are used to store large volumes of data permanently for future use. These are non-volatile in nature. These are less expensive, so most computers have a large amount of secondary storage. However, they don’t operate as fast as primary memory such as RAM. Secondary storage devices are often referred as back-up memory or external memory or additional memory. There are two types of secondary memory. They are: Secondary Memory Magnetic storage Optical Storage Magnetic Tape Magnetic Disk Magnetic Storage External memory where data and instructions are stored in terms of magnetic spot using magnetic coated area is magnetic storage. Basically we have two types of magnetic storage: magnetic tape and magnetic disk. Magnetic Tape It is a plastic ribbon, usually 0.5 inch or 0.25 inch wide and 50 feet to 2400 feet long, with magnetic coating (such as iron oxide) on one side. The tape ribbon is again covered inside reels or on a small cassette. Magnetic tape is the most popular storage medium for long time storage. The tapes can also be erased and reused several times. Old data on the tape are automatically erased and overwritten as new data are recorded in the same area, just like in audio or video tape.
Approved by Curriculum Development Centre 47 Oasis Radiant Computer Science, Book 9 Magnetic Disk Magnetic disk is most popular storage medium for direct access backup storage. It is a thin, circular metal plate or flat rotating disc coated with magnetic material on both sides. Like tapes, disks can also be erased and reused several times. The surface of a disk is divided into a number of concentric circles, called tracks. Each track is further sub-divided into sectors. Each sector typically contains 512 bytes and all are assigned a unique number called sector number. Popular disks are: Hard disk and Floppy disk. Floppy Disk It is a thin, round, flexible plastic, coated with metallic oxide, encased in a square plastic or vinyl jacket cover for protection. It comes in various sizes: 3.5 inches (Micro-floppy) and 5.25 inches (Mini-floppy) in diameter. The advantage of diskette is that it is highly portable and very cheap compared to other secondary storage devices. But now-a-days, people are not using this storage frequently. The capacity of floppy disk varies from 1.44 MB to 2.0 MB. Hard Disks These are most popular secondary storage devices. These are made up of a set of rigid metal diskettes (mostly aluminium) which is permanently sealed in an air-tight metal case. Now-a-days, removable hard disks have been introduced. We can use hard disks externally. The capacity of hard disks varies from some GB to TB. Optical Storage Secondary storage where data is stored in terms of optical spot is optical disk. Due to the use of laser beam technology for writing/reading of data on the disk, these devices are called optical storage devices. This consists of a rotating disk coated with a thin metal or some other material that is highly reflective. The information stored in the disk can be accessed by detecting the light.
Oasis Radiant Computer Science, Book 9 48 Approved by Curriculum Development Centre Optical disks have one long track, starting at the outer edge and growing inwards to the centre. The spiral track is best for reading large blocks of sequential data, such as music. The track of an optical disk is divided into equal length sectors. These are available on various sizes, and the most popular is of 5.25 inch in diameter, whose capacity is around 650 MB, which is roughly equivalent to the total capacity of 550 floppies. So optical disks are the most suitable storage media for multimedia applications: music, movies, clips, and video-games. Types of Optical Disks Popular types of optical disks available in the market are CD-ROM and DVD. CD-ROM (Compact Disk Read Only Memory) It is a shiny, silver colour metal disk of 5.25” diameter. The storage capacity of the disks is 660 MB. These are not reusable disks because we can record the information only one time and can read many times so these are called WORM (Write Once Read Many Times) disk. These are applicable to store applications like dictionaries, music, audio and graphics. Now-a-days we have CDRW. These are modified form of CD’s. Users can rewrite the information on this disk. These are reusable in nature. DVD (Digital Versatile Disk or Digital Video Disk): It is very versatile and capable to store a full-length movie on a single disk. It uses both sides of the disk. Each DVD can store up to 9.4 GB of data . COMPARISON BETWEEN PRIMARY AND SECONDARY MEMORY S.N. Primary Memory Secondary Memory 1. It is a semiconductor memory. It is a magnetic and optical memory. 2. It is high speed, high cost and small sized memory. It is low speed, low cost and large sized memory. 3. Its storing capacity is small. Its storing capacity is very large.
Approved by Curriculum Development Centre 49 Oasis Radiant Computer Science, Book 9 4. Processor directly accesses primary memory. Processor does not directly access secondary memory. It is accessed through I/O interface or I/O Processor. 5. Example: RAM, ROM, etc. Example: Floppy, ZIP- Floppy, Hard Disk, CD-ROM, VCD, etc. Blue Ray It is a new technology replacing DVDs in the future. A blue laser is used to record more data onto a disc which is the same physical size as a DVD. It can store large amounts of data compared to DVDs -- up to 50 GB for dual layered discs. But it is currently expensive compared to DVDs and most computers don’t have Blue ray players/recorders as a standard. Cloud storage Cloud storage means “the storage of data online in the cloud,” wherein a company’s data are stored in and accessible from multiple distributed and connected resources that comprise a cloud. Cloud storage can provide the benefits of greater accessibility and reliability; rapid deployment; strong protection for data backup, archival and disaster recovery purposes and lower overall storage costs as a result of not having to purchase, manage and maintain expensive hardware. However, cloud storage does have the potential for security and compliance concerns. Units of memory measurement The smallest unit of memory measurement is bit (binary digit- 0 or 1). The data stored in a computer is a binary digit, byte, kilobyte, megabyte, gigabyte, terabyte, etc. Bit Bit stands for binary digit. The value of the binary digit is 0 or 1. Nibble Nibble is the combination of 4 bits. Byte Byte is the combination of 8 bits. The units of memory measurements are as follows:
Oasis Radiant Computer Science, Book 9 50 Approved by Curriculum Development Centre S.N. Memory Unit Description 1 Bit 1 Bit = 0 or 1 2 Nibble 1 Nibble = 4 Bits 3 Byte 1 Byte = 8 Bits 4 Kilobyte (KB) 1 Kilobyte (KB) = 1024 Bytes 5 Megabyte (MB) 1 Megabyte (MB) = 1024 KB 6 Gigabyte (GB) 1 Gigabyte (GB) = 1024 MB 7 Terabyte (TB) 1 Terabyte (TB)= 1024 GB 8 Petabyte (PB) 1 Petabyte (PB) = 1024 TB Input Devices Devices which can capture the input from the user are called input devices. Data instructions and programme are given to the computer in the form of input that helps to perform the processing in a computer system. Popular input devices are: Keyboard, Mouse, Scanner, Digital Camera, Digitising tablet, etc. Keyboard Keyboard is a standard input device. The layout of the keyboard is like that of traditional QWERTY typewriter. But it has extra commands and function keys. It has some popular keys for internet, multimedia, operating system and software operation. Some types of standard keyboard: • AT(Advanced Technology): 101 keys • XT(Extended Technology): 83 keys • Enhanced Technology: 103 keys In Apple Macintosh, ABD (Apple Desktop Bus) keyboard is used. It is connected to Apple Desktop Bus. Besides the above types we have wired and wireless keyboard also. Mouse It is a popular pointing device used in a computer. It is also called point and click input device. It has two clicking and one scrolling buttons. There are many technologies