An_Introduction_to_Computer_Science_ClassIX

Authors - Dr. Manojit Ghose Mr. Chandan Kalita Mr. Tarakk Karmaakar Ms. Abha Goswami Ms. Jiri Barman



Foreword Board of Secondary Education, Assam has been following the recommendations of National Cur- riculum Framework (NCF), 2005 for adopting/preparing textbooks of classes IX and X since 2013. As a part of this exercise, several books were prepared and those have been prescribed for class IX and X in Board’s curriculum. Recently, it had been decided to bring about some reforms in the ex- isting textbook of Computer Science for class IX. As such this new textbook of Computer Science has been prepared for class IX students so that they can have the opportunity to study about the latest developments in the subject. I am thankful to all the authors of this textbook for doing their level best in preparing this textbook which helped us to publish the same in time. Moreover, it is a humble request to all the teachers/subject experts/guardians to put their views and suggestions and point out errors, if any, so that we can take necessary steps for its corrections and present a correct version thereafter. The suggestions may be mailed at [email protected]. Secretary Board of Secondary Education, Assam Guwahati



Preface The world is undergoing a digital revolution and computer education has become one of the basic needs of human lives today. Computerization does not only expedite a transaction or improve its efficiency, it also brings accountability and transparency to the systems. Despite numerous challenges thrown to humankind by the recently occurred COVID-19 pandemic, it has indeed positively contributed in giving a major boost to this digital revolution. To embrace this revolution and to draw maximum benefits out of it, our students should be empowered with the fundamental knowledge of computers, recent developments in this field and the upcoming technologies surrounding it. Acquiring knowledge and developing coding skills at an early age will definitely help our students to become job-competent for the coming days in addition to developing logical thinking habits in them. Several innovative initiatives such as Atal Tinkering lab, Robotics lab, ICT in Schools, etc. are run by the govt. and this subject will truly help them there as well. The book “An Introduction to Computer Science” is written in simple English and provides an interactive reading experience. The topics are explained in a lucid manner so that students studying in a vernacular medium can easily understand. The book has 11 chapters in total. We begin every chapter with a relevant quote from a famous person. This is to encourage our students and to tell the significance of topics we discuss in the chapter. Chapter 1 gives an overall introduction of the computer systems: its parts and other basics. In Chapter 2, we discuss Operating Systems, the most important software present in every computer. Chapter 3 talks about office applications - this will enable the students to draft a letter, prepare a presentation, etc. Chapter 4 describes the basics and daily use of the Internet. Chapter 5 provides another aspect of using Information Technology - it talks about ethics, rights, and moral responsibilities while drawing tremendous benefits from these tech- nologies. We are living in a data-driven world and Chapter 6 explains how to store and retrieve data efficiently on computers. Next, in Chapter 7, we come to the popular term of today’s era, that is “coding”. Here, the role of a student changes from a user of the computer to an application developer or programmer. In Chapter 8, we introduce an important programming language called “C”, that is often known as the mother of all programming languages. We continue the discussion on C in Chapter 9 where we present some of the commonly used features of the language. Along with explaining the syntax of a programming language, we emphasize on “thinking like a programmer”. This will enable the young minds to develop programs from a given problem. Chapter 10 briefs some of the recent developments in the domain of computer science. Finally, Chapter 11 concludes the book with some case studies related to the daily applications of computer science in our regular lives.

We understand that students may make silly mistakes when they write programs for the first time. Keeping this in mind, we are making all the C programs presented in this book available online. Students and the teachers can download the C programs for Chapters 8 and 9 along with some additional resources from www.manojitghose.com/seba. We would like to thank the Honourable Chairman, Secretary and other officials of SEBA for providing us an opportunity to author this book. Since the book has been brought out with- in a short span of time, there may be some inadvertent mistakes. We sincerely apologise for that. Suggestions, comments, feedback, and criticism for the authors may kindly be emailed to [email protected]. - Dr. Manojit Ghose - Mr. Chandan Kalita - Mr. Tarakk Karmaakar - Ms. Abha Goswami - Ms. Jiri Barman

Contents CHAPTER - 1 : BASICS OF COMPUTER SYSTEM 1-30 Ü 1.1 Introduction Ü 1.2 Need of Computer Education in Today’s World Ü 1.3 What is a computer ? Ü 1.4 Evolution of Computers Ü 1.5 Generations of Computers Ü 1.6 Usage and limitations of Computers Ü 1.7 Components of Computer System Ü 1.8 Examples of I/O devices Ü 1.9 Hardware and Software Ü 1.10 Performance Measurements of Computer Ü 1.11 Data Representation: CHAPTER - 2 : OPERATING SYSTEM AND ITS IMPORTANCE 31-38 Ü 2.1 Why to Learn Operating System ? Ü 2.2 Need of Operating System : Ü 2.3 Function of Operating System Ü 2.4 Types of Operating Systems Ü 2.5 Some Common Operating Systems Ü 2.6 Difference Between 32-bit and 64-bit Operating Systems Ü 2.7 OS Directory Structure CHAPTER - 3 : OFFICE APPLICATION (MS-Word, MS-Excel, MS-PowerPoint) 39-103 Ü 3.1 What is Word Processor ? Ü 3.2 Features of a Word Processor Ü 3.3 Application of a Word Processor Ü 3.4 Introduction to Microsoft Word Ü 3.5 Introduction to Spreadsheet Ü 3.6 Basic Feature of Spreadsheet Programs Ü 3.7 Application of Spreadsheet Ü 3.8 Exp`loring Microsoft Excel Ü 3.9 Introduction to Presentation Ü 3.10 Features of Presentation Software Ü 3.11 Application of Presentation Software Ü 3.12 Introduction to Microsoft PowerPoint CHAPTER - 4 : INTRODUCTION TO INTERNET 104-116 Ü 4.1 What is internet ? Ü 4.2 Structure Ü 4.3 Client and Server Ü 4.4 Protocol Ü 4.5 History of the internet. Ü 4.6 Internet Connection Ü 4.7 Browser Ü 4.8 World Wide Web (WWW) Ü 4.9 Website Ü 4.10 Uniform Resource Locators (URL) Ü 4.11 Search Engine Ü 4.12 Electronic Mail CHAPTER - 5 : ETHICS IN IT 117-124 Ü 5.1 Introduction to Information Technology Ü 5.2 Ethics in Information Technology Ü 5.3 Plagiarism

Ü 5.4 Intellectual Property Rights Ü 5.5 Security and Integrity of Information Ü 5.6 Network Security Ü 5.7 Firewalls Ü 5.8 Antivirus Ü 5.9 Internet Security Ü 5.10 Password Security Ü 5.11 Users’ Privacy Ü 5.12 Cybercrime Ü 5.13 Software Piracy CHAPTER - 6 : DATABASE PART I 125-139 Ü 6.1 Introduction Ü 6.2 Need for a Database Ü 6.3 Contents of a database Ü 6.4 Uniqueness of Record Ü 6.5 Primary Key Ü 6.6 Super Key Ü 6.7 Candidate Key Ü 6.8 Relational Database Ü 6.9 Foreign Key Ü 6.10 What is MS Access? CHAPTER - 7 : C ODING AND ITS IMPORTANCE 140-145 Ü 7.1 An introduction to coding Ü 7.2 Programming languages Ü 7.3 Problem solving in computer Ü 7.4 Algorithm, Flowchart and Pseudocode CHAPTER - 8 : INTRODUCTION TO C PROGRAMMING 146-155 Ü 8.1 Introduction to C programming language Ü 8.2 The preliminaries Ü 8.3 Writing our first C program Ü 8.4 Understanding the C program Ü 8.5 Compilation of a C program: Behind the scene Ü 8.6: Using escape sequence in printf() CHAPTER - 9 : EXPLORING C PROGRAMMING LANGUAGE 156-169 Ü 9.1 Identifiers and keywords Ü 9.2 Variable, data types and format specifiers Ü 9.3 Operators in C Ü 9.4 Conditional statements CHAPTER - 10 : RECENT DEVELOPMENTS IN IT 171-179 Ü 10.1 Computer hardware Ü 10.2 Artificial intelligence and machine learning Ü 10.3 Recent application domains Ü 10.4 Computing as a utility service CHAPTER - 11 : CASE STUDIES : APPLICATIONS OF IT IN DAILY USE 180-181 Ü 1. Discussion of different career options and opportunities in Information Technology. Ü 2. Making your biodata in MS-Word Ü 3. Creating a brochure for your school in MS-Word Ü 4. Creating report chart in MS-Excel Ü 5. Creating a presentation in MS-PowerPoint with biography of great personalities of India.

BASICS OF CHAPTER 1COMPUTER SYSTEM “Computers are incredibly fast, accurate and stupid: humans are incredibly slow, inaccurate and brilliant: together they are powerful beyond imagination.” - Albert Einstein In this chapter, we will learn the definition and various features of computer and discuss about the need of computer education. We will see how computers have evolved and will also read about the major developments in technology that have led to the devices that we use today. We will see how computers are used in different areas of our day-to-day lives. In this chapter we will also learn about the basic components of a com- puter system. We will read about some I/O devices that are widely used these days. We will also focus on different types of software. This chapter also covers the different number systems used in digital computer and the tech- niques used in converting a number of one base to another base. So, the goal of this chapter is to familiarize you with the basics of a computer system. 1.1 INTRODUCTION Computer is the most versatile electronic machine man has ever created. Computers have made a great impact in our everyday life. Computers are transforming the way we communicate, learn and work. So, it is very essential for every person today to have basic knowledge of a computer system. Accordingly, this chapter includes the basic knowledge of a computer system. 1

1.2 NEED OF COMPUTER EDUCATION IN TODAY’S WORLD By computer education, we mean learning basic knowledge about computers as well as acquiring skills to operate computers efficiently to perform better jobs. A few decades ago, computer’s use was mostly relegated to a handful of professions. Today, computers are used in almost every field. Computers are widely used in educational institutions, government offices, businesses, banks, hospitals, railway stations, airports, entertainment, defense, transportation, reservation, for searching the Internet for information and in many other fields. With the advancement of technology and wide use of computers, the demand of computer literates is increasing everyday. Computer literacy is the need of the day today. So computer education is becoming an inseparable part of education. There are many clear advantages of being computer literate. Some of them are mentioned below to understand the need of computer education: „ Computer education enhances creativity and thinking skills of students. „ Computer education provides efficient and better use of technology. Most of the technology depends on computer systems. So computer education helps to use technology efficiently. „ Computer education provides more job opportunities. Computer education is very important to build up a strong career. „ Computer education proves beneficial for better communication. A significant part of communication in today’s world is done remotely over computer networks. To use the facilities of communication using a computer, computer education is needed. „ Computer education improves research skills and helps in communicating with different education institutions. Everybody should know how to use a computer system and the resources associated with it to improve their own research skills. „ Computer education helps in creating a better education environment. To use the facility of smart classroom, computer education is necessary. „ Computer education connects people to the online world. Everything today is becoming online. To use all the facilities of e-sites, computer education is required. As the time is passing, technology is evolving. So to cope with the advancement of technology, it has become important for all of us to gain computer education. Computer education increases efficiency of a person and helps us in being prepared for a digital future. 1.3 WHAT IS A COMPUTER ? A computer is an electronic device that performs a function based on a given set of instructions called a program. Programs enable computers to perform an extremely wide range of tasks. Computers cannot do anything without a program. A computer accepts data, processes it and produces information. Data means raw facts and figures. Information means processed data or meaningful data. Data can be anything. For example, marks obtained by a student in various subjects and his roll number form data. Computer prepares 2

result sheets using these data, which is the information. The process of turning data into information to increase their usefulness and adding values for a particular purpose is known as data processing. Input, processing and output- these three basic steps constitute the data processing cycle. Today, computers are used in almost every field. The first electronic computers were used to perform difficult numerical calculations. But now computers perform a diverse array of services and functions. The usefulness of a computer is mainly due to the following advantages or features: 1. Speed : Computers can carry out millions of instructions per second. The speed of computers is usually given in nanoseconds and picoseconds, where 1 nanosecond = 1x10-9 seconds and 1picosecond = 1x10-12 seconds. 2. Accuracy : Computers work at a very high speed without losing accuracy. It always gives accurate results, provided the correct data and set of instructions are provided as input to it. 3. Diligence : Unlike humans, computers do not get tired of performing repetitive tasks. 4. Storage capacity : Computers have the ability to store data and programs. The data and programs stored can be retrieved and used whenever required. 5. Versatility : Computers can do different types of tasks efficiently. 1.4 EVOLUTION OF COMPUTERS The present computer system has evolved after centuries of efforts from different intellectuals who contributed through their works during different periods of time. Let us take a look at the evolution of computer. The evolution started from the 3500 BC, when human being first started to learn to calculate with a calculating machine called abacus. Abacus (Figure : 1.1) : The abacus, also called a counting frame, is a calculating device that was used in Mesopotamia around 3500 BC. The Mesopotamians quite unknowingly laid the foundation of the computed era. An abacus consists of beads divided into two parts which are movable on the rods of the two parts. This device permits the user to represent numbers by the position of beads on a rack. Simple calculations can be carried out rapidly and efficiently by positioning the beads appropriately. Although, the abacus was invented around 3500 BC, it is interesting Figure : 1.1 to note that it is still used. Napier’s Bones (Figure : 1.2 ) : In the 17th century, the Scottish mathematician Sir John Napier invented this manually operated calculating device. Napier’s bones are numbered rods which can be used to perform multiplication of any number by a single digit number. This set is composed of ten bones; nine of which display the multiples of a given number between one and nine. Each bone is divided into ten squares. The tenth bone, known as the index, displays the numerals 1 through 9. It was used to Figure : 1.2 represent the multiplier. The digits of the multiplication table are split by a diagonal line. 3

Pascal’s adding machine (Figure : 1.3) : One of the first semi-automatic mechanical devices, Blaise Pascal, a French mathematician, developed it in 1642. It was based on gear wheels, with the digit 0 through 9 displayed around the circumference of each wheel. He designed the machine to add and subtract two numbers directly and to perform multiplication and division through repeated addition or subtraction. Figure : 1.3 Leibnitz’s calculator (Figure : 1.4) : Gottfried Leibnitz, a German mathematician improved an adding machine and constructed a machine called Leibnitz’s machine in 1671. It was able to perform multiplication and division also. The machine performed multiplication through repeated addition of numbers. Leibnitz’s machine used stepped cylinder each with nine teeth of varying lengths instead of wheels as was used by Pascal. Figure : 1.4 Jacquard’s Loom (Figure : 1.5) : The Jacquard Loom is a mechanical loom, invented by Joseph Jacquard, first demonstrated in 1801. He manufactured punched cards and used to control the looms. The entire control weaving process was automatic. The entire operation was under a program’s control. The invention of punched cards influenced the later advancements. Figure : 1.5 Babbage Difference Engine (Figure : 1.6) : Charles Babbage, an English mathematician, developed a machine called Difference engine in the year 1822.Charles Babbage is often called the father of the modern computer. The difference engine was made to calculate various mathematical func- tions. The machine was capable of evaluate polynomials using the method of difference. Figure : 1.6 Analytical Engine (Figure : 1.7) : In 1833, Charles Babbage designed Figure : 1.7 a machine Analytical Engine, which was to become a real ancestor of the modem general purpose computer. Analytical engine was capable of performing all four arithmetic operations as well as comparison. He included the concept of central process, storage area, memory and input-output devices in his design. 4

Hollerith’s Machine (Figure : 1.8) : In 1887, an American named Herman Hollerith invented the tabulating machine which was the first electromechanical calculating device. He used punched cards for storing and processing information. This machine was used by American Department of Census to compile their 1880 census data. Figure : 1.8 Mark I (Figure : 1.9) : In 1943, American Computer Engineer devised the first electromechanical computer named Mark-I. It was able to multiply two 10-digit numbers in 5 seconds. Mark-I was the first machine which could perform to pre programmed instruction automatically. It was the first operational general purpose computer. Figure : 1.9 1.5 GENERATIONS OF COMPUTERS Generation of computer refers to the different advancements of new computer technology. Generation of computer is often used in relation to the hardware of computers. With each new generation of computers, the circuitry becomes smaller and more advanced than that used in the previous generation. Each generation is characterized by a significant technological development. There are five definable generations of computers. There is no clear line of distinction between these generations, as there is a certain amount of overlapping in technologies between them. First generation (1939 - 1954) : The first generation computers used vacuum tubes for circuitry and magnetic drums for storage. Sizes of these computers were as large as the size of a room. The first-generation computers were very expensive and used for scientific purposes. First generation computers could be programmed in machine language, consisting of only 0s and 1s. These computers were limited to solving one problem at a time. Input was fed using punched cards and paper taps and output was generated as printouts. Some computers of this generation are given below : Atanasoff Berry Computer: It was the first electronic digital computer. It was a special-purpose computer and designed to solve systems of linear equations. ENIAC (Electronic Numerical Integrator and computer): It was the first fully electronic general- purpose computer. EDSAC (Electronic Delay Storage Automatic calculator): It was built on the stored program architecture for computers proposed by the scientist and mathematician John Von Neumann. The program was fed into its memory unit using paper tape. It was slightly faster than ENIAC. EDVAC (Electronic Discrete Variable Automatic Calculator): It could hold both a program and data in memory. UNIVAC I (Universal Automatic Computer I): It was one of the first commercially available computers. 5

Second Generation (1955 - 64) : Second-generation computers were manufactured using transistors instead of vacuum tubes. Transistors were highly reliable compared to tubes. Due to the properties of transistors, the second-generation computers were more powerful, more reliable, less expensive and smaller than the first-generation computers. Another major event during this period was the invention of magnetic cores for storage. Mag- netic disk and magnetic tapes were the main secondary storage in second generation computers. While the first-generation computers were programmed using machine language, the second-generation computers moved towards symbolic or assembly languages. High level languages like FORTRAN, CO- BOL, ALGOL and SNOBOL were also being developed. Examples of some second-generation computers include IBM604, IBM1401, IBM1620, IBM 7094, CDC 11604, CDC 3600, and UNIVAC 1108. Third Generation (1965 - 1975) : The third-generation computers replaced transistors with Integrated Circuits (IC), known as chips. The integrated chips drastically increased the speed and efficiency of computers. The third generation computers were more powerful, more reliable, relatively less expensive and faster. IBM’s 360 series and 370 series computers are examples of third-generation computers. Fourth Generation (1976 - Present): The next advancement in computer technology was the microprocessors. The microprocessor launched the fourth-generation computers. Semiconductor memories replaced magnetic core memories. IBM’s Personal Computer (PC) and Apple’s Macintosh are examples of fourth-generation computers. Fourth generation computers became more powerful, compact, reliable, and affordable. As a result, it gave rise to Personal Computer (PC) revolution. The faster accessing and processing speeds and increased memory capacity helped in many new operating systems. Graphical User Interface (GUI) made computers more user-friendly. Fifth generation (Present and beyond) : The fifth-generation computer system was an initiative by Japan’s Ministry of International Trade and Industry, begun in 1982. Fifth-generation computers are based on the concept of artificial intelligence (AI). AI is an emerging branch in computer science, which interprets the means and methods of making computers think like human beings. Parallel processing and superconductor technology have made AI a reality. In parallel processing, many processors are grouped to function as one large group processor. A super- conductor is a conductor through which electricity can travel without any resistance resulting faster transfer of information between the components of a computer. Fifth-generation computers are still in development, though there are some applications, such as voice recognition, programs that could translate documents from one language to another. 1.6 USAGE AND LIMITATIONS OF COMPUTERS Today, computers are used almost everywhere. Here are some of the areas where computers are in use widely. 6

¿ Education : Computers are used in education sector for taking online classes, online examinations, referring e-books, online tutoring etc. A computer is a powerful teaching aid. Teachers use computers to prepare lessons. Students use computers to access Internet, do projects and research works. ¿ Home : Computers are used at homes for several purposes like watching movies, online bill payment, home tutoring, playing games, internet access, social media access, etc. Computers help to avail work from home facility for corporate employees. ¿ Medical Field : Computers have become an important part in hospitals, labs and pharmacies. Computers are used to keep records of patients and medicines. Computes are used in diagnostic system and patient monitoring system. ¿ Business : Almost every business uses computers nowadays. Computers are used for maintaining staff records, transaction processing, sales forecasting, production planning, create presentation and reports, etc. ¿ Government : Various government department use computers to improve the quality and efficiency of their services. Computers are used to keep records on legislative actions, Internal Revenue Service, etc. ¿ Banking and Finance : In the banking sector, computers are used to store the details of customers and conduct transactions. People can also use computer to access information on stock markets, trade stocks, and manage investments. ¿ Communication : Computers are used to communicate through e-mails, chat, and video conferencing. ¿ Entertainment : Computers are used to listen to music, watch movies online, play games. Computers are used to create cartoons, animations, videos, etc. Computers are used in recording music. ¿ Reservations : Computers are used for airline/railway/bus tickets reservations. People can book their tickets irrespective of their location. For example, a person in Guwahati may book a ticket from Kolkata to New Delhi. ¿ Science and Engineering : Computers with high performance are used for engineering purpose and to stimulate dynamic process in Science. Computers are used by the scientists for research works, sending and launching artificial satellites. ¿ Military : Computers are largely used in defense. Computers are used in military communication, missile control, military operation and planning etc. Limitations of computer : The computer system does not have the power to make decisions on their own because they do not possess all the essentials of decision making. They can be programmed to take decisions. If a computer has not been programmed for a particular decision making situation, it will not respond due to lack of wisdom and evaluation faculties. It cannot respond in a particular situation unless that situation is already programmed into them. Computers are programmed to complete each and every task. A computer can do any task; all that it requires is the right program to do it. 7

1.7 COMPONENTS OF COMPUTER SYSTEM A COMPUTER BASICALLY PERFORMS FIVE MAJOR OPERATIONS : ¢ Accepting data or instructions ¢ Processing data ¢ Storing data ¢ Displaying results ¢ Controlling and coordinating all operations inside a computer A computer system consists of a unit to perform each of the above functions. Figure : 1.10 : Block diagram of a computer Input Unit : The Input unit consists of input devices that are attached to the computer. Examples of input devices are; keyboard, mouse, scanner, microphone etc. These components help the users to enter data and commands into a computer system. Input unit converts data into computer understandable form i.e. the binary code. Since computer is a electronic device, it can understand only two stages ON /OFF or High/Low voltage or the binary code that uses just two symbols: 1 for ON and 0 for OFF. Output Unit : The output unit consists of the output devices attached to the computer. These devices are needed to get output from the computer. The two most commonly used output devices are the monitor and the printer. 8

The output coming from the CPU is in the binary form, it must be converted to human readable form, before supplying the results to the outside world. This function of conversion is performed by output units. Central Processing Unit (CPU) : The CPU is the brain of the computer system. In a computer system, all calculations and com- parisons are made inside the CPU and the CPU is also responsible for activating and controlling the operations of other units of a computer system. The CPU, also the processor, is the most important part of the computer. The CPU consists of three basic components: i. Arithmetic and Logic Unit (ALU) ii. Control Unit (CU) iii. Registers Arithmetic and Logic Unit (ALU) : The ALU does arithmetic calculation and takes logical decisions. ALU performs all the arithmetic (+, -, x, /) and logical (<, >, =, <=,>=) operations. Control Unit (CU) : The control unit of a computer system manages and coordinates the operations of all the other components of the computer system. It acts like our central nervous system. It does not process the data but it controls the entire processing of data inside the computer. Registers : Registers are high speed temporary storage area. Registers are used to quick accept, store, and transfer data and instructions that are being used immediately by the CPU. The registers are very fast computer memory which is used to execute programs and operations efficiently. Reg- isters work under the direction of the control unit. These parts are connected to the rest of the computer through buses. The buses are electrical wires which connects the various components and transfer data between them. There are three main buses. These are : Data bus : It carries data from the memory to the CPU and the CPU to the memory. Address bus : It carries address from the CPU to the memory. Control bus : It carries instructions between the CPU and other parts of the computer. Memory Unit : Computer memory is the storage space in the computer. The memory unit provides space for storing data and instructions, space for intermediate results, and also space for the final results. Units of Memory : A bit is an elementary unit of memory. Bit is the short form of binary digit. A bit can be ei- ther 0(representing OFF/Low voltage) or 1(representing ON/High voltage). Data in a computer are stored in the form of strings of 0s and 1s. A group of four bits is called nibble. It can store one decimal digit in its binary form. A group of eight bits is called a byte. One byte is the smallest unit which can represent a data item or a 9

character. A word, like a byte, is a group of fixed number of bits processed as a unit, which varies from computer to computer depending on architecture of the computer. A word may be of 8, 16, 32, or more bits. Each word of information is retrieved or stored as a unit in the computer. Table 1.1 : Units of Memory measurements Types of Memory There are broadly two types of memories in a computer system: 1. Internal memory or Main memory or Primary memory : All computers have internal memory to store programs and data while the computer is running. Primary storage area does the following operations: i. It holds input data and instructions. ii. It holds data that is being processed and the processing instructions. iii. It holds intermediate results of processing. iv. It holds final result of processing. The main memory of a computer is made up of two parts: i. Random Access Memory (RAM) (Figure : 1.11) : RAM holds data, programs and instructions for computer. The CPU can access data directly from RAM almost immediately. The contents of RAM can be accessed randomly, i.e., in any order. It is also called Read/Write memory. Read/Write memory means that we can read from this memory and can also write on it.RAM is temporary or volatile. Volatile means that, its contents are lost as soon as soon as the power to the computer is switch off. 10 Figure : 1.11

RAM may be classified as dynamic and static. Static RAM (SRAM) retains the stored informa- tion as long as the power supply is on. Dynamic RAM (DRAM) slowly loses the stored information even when the power supply is on, and has to be refreshed periodically. ii. Read Only Memory (ROM) (Figure : 1.12) : In ROM, information once stored remains fixed i.e., it cannot be changed. So, ROM can only be read and used. The contents of ROM are written by the manufacturer and come along with the computer. ROM stores basic input/output instructions to operate the computer. ROM only allows reading; we cannot write on it. ROM is non-volatile i.e., its contents are retained even when the power supply to the computer is switched off. Figure : 1.12 Various types of ROMs : PROM (Programmable Read Only Memory) is read-only memory that can be programmed to store information only once by a user. It is not erasable. EPROM (Erasable Programmable Read Only Memory) can be reprogrammed to record different information. The recorded information can be erased by exposing it to ultra-violet light. EEPROM (Electrically Erasable Programmable Read Only Memory) can be programmed and erased electrically. 2. External memory or Secondary memory or Auxiliary memory : Since the computer’s primary memory is temporary, secondary memory devices are used to store data and programs permanently for later use. The secondary memory is non-volatile. Primary memory has a limited storage capacity. So secondary memory devices are used to store large amount of data. There are various types of secondary storage devices. These storage media can be broadly divided two categories: magnetic and optical media. Magnetic media is coated with a magnetic layer. In optical media information is stored and read by laser beam. Some most common secondary storage devices are: Magnetic media : i. Floppy disks A floppy disk is a flexible disk with a magnetic coating on it. These are one of the oldest type of portable storage devices that could store up to 1.44 MB of data. Now floppy disks are not used due to very less memory capacity storage. ii. Hard disks (Figure : 1.13) : A hard disk is a basically a set of disks known as platters, each with its own read/write head. These rotating disks are coated with a magnetic material and stacked with space between them. Data is recorded on the surface of the disks magnetically. Figure : 1.13 11

iii. Magnetic tapes Magnetic tapes can hold a large amount of data. Magnetic tapes are available in the form of cassettes, reels, and cartridges. Optical media : i. Compact Disk (CD) (Figure : 1.14) : The CDs have storage capacity of upto 700 MB. There are three types of CDs: CDROM (CD-Read Only Memory), CD-R (CD-Re- cordable) and CD-RW (CD-Rewritable). ii. Digital Versatile Disk (DVD) Figure : 1.14 DVDs can store six times more data than CDs. A DVD can hold upto 17 GB of data. There are three types of DVDs: DVDROM (DVD-Read Only Memory), DVD-R (DVD-Recordable) and DVD-RW (DVD-Rewritable). iii. Blue-ray disk (Figure : 1.15) : It is similar to a CD or DVD but can store upto 17 GB of data. iv. Solid State : Some examples of solid state storage devices are pen drive, memory stick and smart card. Pen drive, also called USB drive can be used to store, access, and transfer data. It is popular because it is easy to use Figure : 1.15 and small in size. A memory stick and card is used as a storage media for a portable device like a mobile phone and digital camera. These storage devices use flash memory. Flash memory is an electronic non-volatile storage medium that can be electrically erased and reprogrammed. memory cards are also a solid state devie which are very small storage device. These can be used im Mobile Phones, Laptops, Digital Camera etc. Memory Card can be easily inserted or removed from the device. 1.8 EXAMPLES OF I/O DEVICES Figure : 1.16 INPUT DEVICES Keyboard (Figure : 1.16) : The keyboard is a basic input device used to enter data into a computer. The layout of the keyboard is like that of a typewriter, with some additional keys. Each key, when pressed, sends a digital code to the computer. The computer uses these codes to represent a quantity. Mouse (Figure : 1.17) : Figure : 1.17 The mouse is the most popular pointing device. A pointing device helps users to have control over the movements of an on-screen pointer. 12

Trackball (Figure : 1.18) : A trackball is an alternative to a mouse. It is usually used in laptops, where it is placed on the keyboard. Figure : 1.18 Joystick (Figure : 1.19) : A joystick consists of a vertical stick that can be moved in all directions to control the movement of the pointer on the screen. It is used to play computer games. Figure : 1.19 Figure : 1.20 Scanner (Figure : 1.20) : A scanner is used to convert a written document or a photo graph into digital file. There are different types of scanners : i. In flatbed scanner, the document to be scanned is placed face-down of a flat glass surface. ii. A drum scanner uses rolling drum. The sheet to be scanned is fed through the scanner so that the drum rolls over the entire sheet. iii. Hand-held scanner performs scanning documents just like a flatbed scanner, but it is very small which can be held in a hand. Microphone (Figure : 1.21) : A microphone is an input device which converts human speech into electrical signals. Figure : 1.21 Barcode reader (Figure : 1.22) : A barcode reader is used to read information stored in a barcode. Barcode is a system of representing data using machine-readable lines. Figure : 1.22 13

Figure : 1.23 Light Pen (Figure : 1.23) : It is a light-sensitive input device shaped like writing pen. It is used to draw on the computer screen or to make menu selections. Touch screen : Now a days touch screen are used as input device in mobiles and tablets. OMR (Optical Mark Reader) It can recognize a pre-specified type of mark made by pencil or pen. It is commonly used for evaluating specially designed multiple-choice question answer sheets. MICR (Magnetic Ink Character Reader) It can read the magnetized ink characters. It is used to read the characters printed on bank cheques. OUTPUT DEVICES Figure : 1.24 Monitor (Figure : 1.24) : The VDU (Visual Display Unit) or monitor is similar to a television screen. It displays both text and graphics. The output produced on a VDU is called a soft copy. The picture on a monitor is made up of thousands of tiny dots called pixels. Cathode ray tube (CRT) and liquid crystal display (LCD), Plasma monitor, touch screen monitors are different types of monitors available now a days. LCD screen are also used in mobiles and tablets displays. Printer (Figure : 1.25) : A printer is a device that takes the text and graphics information obtained from a computer and prints it on to a paper. The output produced on a paper is called the hard copy. Figure : 1.25 Printers can be divided into two distinct categories: i. Impact printer In these printers, there is a physical contact between the print head and paper. Impact printers are subdivided into line printers and character printers. 14

Line printer prints one line of text at a time. Examples of line printers are- drum printer and chain printer. Character printer prints one character of text at a time. Examples of character printers are - Dot matrix printer, letter-quality printer. ii. Non-impact printer In these printers, there is no physical contact between the print head and paper. Non-impact printers are faster than impact printer. The main types of non-impact printers are inkjet printer, thermal printer, electromagnetic printer, and laser printer Speaker (Figure : 1.26) : A speaker is an output device that allows us to hear sounds from the computer. It receives the sound in the form electric current from the sound card and then converts it to sound. Figure : 1.26 Plotter (Figure : 1.27) : The plotter is a graphics output device used to create graphics on a paper. Plotters are widely used to draw maps, to draw engineering and architectural drawings. Figure : 1.27 Projector (Figure : 1.28) : Figure : 1.28 A projector is an output device that takes the display of a computer and projects a larger version of it onto a screen. It may be used as an alter- native to a monitor when showing video or images or presentations to a large group of people. 1.9 HARDWARE AND SOFTWARE A computer system comprises of both hardware and software. Hardware represents to the physical components of a computer system. These components can be seen and touched. Input devices, output devices, CPU, memory devices etc are examples of hardware. Software represents the set of programs that directs the computer how to work. A program is a set of instructions to perform a specific task. Computer hardware cannot do anything on its own. It needs software to instruct what to do. Computer software is written by programmers using programming languages. 15

Computer software can be classified into two categories : 1. System software 2. Application software System software System software is a set of programs designed to operate hardware and control the internal operations of a computer. System software provides a platform for running application software. System software can be further classified into Operating system, languages processors and Utilities. Operating System An operating system is an interface between a computer user and computer hardware. It runs the computer. The purpose of operating system is to provide an environment in which a user can execute a program in a convenient and efficient manner. Every computer system must have at least one operating system to run other programs. Examples of operating system: Windows, Linux, Android etc. Language processors (Translators) Computer does not understand any language other than binary or machine language. Language processors are system software that translate programs written in assembly level language or high level language into its equivalent machine language program. Assembler, compiler and interpreter are language processors. An assembler converts the program written in assembly language into machine language. A compiler and an interpreter convert the program written in high level language into machine language. A key difference between compiler and interpreter is that a compiler converts the program in one go while an interpreter translates the program line by line. Utility software (Utilities) Utilities are programs that add functionality to the computer system. Utilities ensure the smooth functioning of the computer. Some examples of utility programs: I. Antivirus software used to scan the computers for viruses. II. Backup utilities used to make a copy of all information stored on disk. III. File management program that manages the files and folders on a computer system. IV. Encryption / Decryption software used to encrypt or decrypt data. Encryption is the process that coverts data into coded form, which cannot be understood by unauthorized user. Decryption is a process that converts coded data to readable form. Application software (App) Applications software is a set programs developed to carry out complete operations for a specific purpose. These are the programs written by the programmers to perform a specific task. Payroll processing software, examination processing software etc. are examples of application software. 16

Application software can be further divided into two categories : 1. General-Purpose Application software (Packages) General-purpose application software is designed to perform a wide range of tasks. Examples of general-purpose packaged software are as follows : I. Word-processing software, used to entering, editing, formatting and printing text. Examples: Microsoft Word, Google Docs, Wordperfect, Abiword etc. II. Spreadsheet software, used to enter data values in a tabular form, specify formulae and ma nipulate large amount of data. The spreadsheets are used to calculate, compare, analyze data, and to generate graphs and charts. Examples: Microsoft Excel, Lotus1-2-3, QuattroPro etc. III. Presentation software, used to create slide show presentations. Examples: Microsoft PowerPoint, Google slides etc. IV. Database management software, used to manage a database. A database refers to a collection of logically related data. A database management software provides the necessary tools to create and manipulate the data in the database. Examples: Microsoft Access, Oracle etc. V. Thousands of Apps on mobiles. 2. Specific-Purpose Application Software Specific-purpose application software are designed to perform specific tasks. Examples of specific-purpose packaged software are as follows: I. Accounting Management Software, used to manage the entire financial records of a business. II. Payroll System, used to calculate the salary of employees and generates payslips. III. Reservation System, used for online reservation of railway and airline tickets and also for movies etc. IV. School inventor control system, used to manage the school assets. 1.10 PERFORMANCE MEASUREMENTS OF COMPUTER Computer performance is the efficiency of a given computer system, or how well the computer system performs. It depends on response time, throughput and execution time of a computer system. Response time is the time from start to completion of a task. Throughput is the total amount of work done in a given time. CPU execution time is the total time a CPU spends computing on a given task. Performance is inversely proportional to CPU execution time. How to improve the performance ? There are many factors that can affect performance of a computer system. Three of them are discussed below: i. CPU speed The speed of the CPU is measured in either Megahertz (MHz) or Gigahertz (GHz). A 1 MHz CPU can carry out one million instructions per second. A 1 GHz CPU can carry out 1 billion instructions per second. So upgrading CPU to faster one is one way to improve computer per formance. ii. Memory size Another way to improve the speed of the computer system is to upgrade RAM. If your com puter has a small amount of RAM, you could add extra RAM chips. 17

iii. Number of Programs If you open more programs, files and documents, the RAM will fill faster and your computer will appear to slow down. So to improve the performance of your computer, you have to limit the number of programs running at a time. You have to limit the number of files/documents opened at one time. 1.11 DATA REPRESENTATION: Data representation refers to the form in which data is stored, processed, and transmitted. Computers store data in digital formats that can be handled by electronic circuitry. The user input is first converted and transmitted as electrical pulses that can be represented by two unique states ON and OFF. These two states are represented by the binary 0 and 1. A binary digit is also called a bit. So, a bit can either be 0 or 1. When data is entered into a computer, it must be converted into the bits of memory. For example, if we input a number 197, the number 197 will first converted into its equal binary form 11000101 and then stored into the memory. Similarly, if we input a character ‘A’, then its binary equivalent form 01000001 is stored in the memory. Digital Number System : In digital system like computers, the quantities are represented by symbols called digits. Many number systems are in use in digital technology that represent the digits in various forms. The most common number systems used are- decimal, binary, octal, and hexadecimal systems. Let us discuss these number systems briefly. Decimal Number System : The decimal system is composed of ten digits or symbols. These symbols are 0,1,2,3,4,5,6,7,8,9. The decimal system is also called the base-10 number system because it has 10 digits. The decimal system is a positional-value system in which the value of a digit depends on its position. For example, consider the decimal number 524. Here, the digit 5 actually represents 5 hundreds, the 2 represents 2 tens, and the 4 represents 4 units. In decimal numbers, the place value goes up in factors of ten. The 5 carries the most weight of three digits and it is referred to as the most significant digit (MSD). The 4 carries the least weight and is called the least signifi- cant digit (LSD). Binary Number System : In the binary system there are only two symbols, 0 and 1.The binary number system uses base 2. This base-2 system can be used to represent any quantity that can be represented in a decimal or other number system. The binary system is also a positional-value system. Each binary digit has its own value or weight expressed as a power of 2. For example, consider the binary number 1011. The rightmost digit has a place value of 1x20 while the leftmost has a place value of 1x23. The leftmost bit of a binary number carries largest weight and hence, is called the most significant bit (MSB). The rightmost bit of a binary number carries the smallest weight, and hence called least significant bit (LSB). 18

It is very easy to design electronic circuit that operates with only two voltage levels. Therefore, almost every digital system uses the binary number system. Octal Number System : The octal number system has eight unique symbols: 0, 1, 2, 3, 4, 5, 6, 7. Thus, octal number system is base-8 number system. The octal number system is also a positional value system. Each octal digit of an octal number has its own value or weight expressed as a power of 8. Hexadecimal Number System : The hexadecimal number system is the base-16 number system. This number system uses 16 possible digits or symbols. It uses the digits 0 to 9 and the symbols A to F. The symbols A, B, C, D, E, and F represent the decimal values 10, 11, 12, 12, 14, and 15 respectively. In the hexadecimal number system, therefore, the letters A through F are number digits. The number A has a decimal equivalent value of 10 and the number F has a decimal equivalent value of 15. The hexadecimal number system is also a positional-value system. Each hexadecimal digit has its own value or weight expressed as a power of 16. Number conversions : In a digital system, three or four of these number systems may be in use at the same time. So we need to know the conversion technique between them. There are many methods or techniques which can be used to convert numbers from one base to another. Decimal to Binary conversion : The conversion of decimal to binary can be done by repeated-division method. In this method, the number is successively divided by 2 and its remainders recorded. The final binary result is obtained by assembling all the remainders, with the last remainder being the most significant bit (MSB). 19

Decimal Fractions to Binary: To convert a decimal fraction into binary, the procedure is to successively multiply the decimal fraction by 2 (the base) and record all the numbers to the left of the decimal point. Reading down these numbers, the final binary result is obtained. Binary to decimal conversion : In order to convert binary number into its decimal equivalent, the procedure is to find the products of each digit value (0 or 1) and its positional value, and then to add all the products. Binary Fractions to Decimal Conversion : In order to convert binary fraction into its decimal equivalent, the procedure is to find the products of each digit value (0 or 1) and its positional value, and then to add all the products. 20

Decimal to Octal Conversion : A decimal number can be converted to octal by using the same repeated-division method that is used in the decimal to binary conversion. But here the division is done by 8 instead of 2. The first remainder becomes the least significant digit (LSD) and the last remainder becomes the most significant digit (MSD) of the octal number. Decimal Fraction to Octal Conversion : To convert a decimal fraction into octal, the procedure is to successively multiply the decimal fraction by 8 (the base) and record all the numbers to the left of the decimal point. Reading down these numbers, the final octal number is obtaine Octal to Decimal Conversion : In order to convert octal number into its decimal equivalent, the procedure is to find the products of each octal digit and its positional weight, and then to add all the products. 21

Decimal to Hexadecimal Conversion : Like decimal to binary and decimal to octal conversion, decimal to hexadecimal conversion can be done using repeated-division method by 16. Note that, any remainder that is greater than 9 are represented by letters a through F. Example : Convert 42410 into Hexadecimal Solution : Decimal Fraction to Hexadecimal Conversion : Like decimal fraction to octal conversion, to convert a decimal fraction into hexadecimal, the procedure is to successively multiply the decimal fraction by the base (16 here) and record all the numbers to the left of the decimal point. Reading down these numbers, the final hexadecimal number is obtained. Hexadecimal to decimal Conversion: Try to recall what we did to convert octal number into its decimal equivalent; the same procedure will be applied to convert a hexadecimal number into to decimal equivalent. The only difference is that here we will use base 16 instead of 8. In order to convert octal number into its decimal equivalent, multiply each hexadecimal digit by its positional weight, and then add all the products. 22

Octal to Binary Conversion : Since there are only 8 digits in the octal number system, 3 bits (23=8) are sufficient to represent any octal digit in binary. In order to convert octal number into its binary equivalent, the procedure is to convert each octal digit to a 3-bit binary equivalent and combine all the resulting binary groups (of 3 digits each) into a single binary number. Binary to Octal Conversion : To convert binary into octal number, the bits of the binary number are grouped into groups of three bits starting at the LSB. Then each group of three bits is converted to its octal equivalent digit. Since decimal digits 0 to7 are equal to octal 0 to 7, binary to decimal conversion can be used in this conversion. 23

Hexadecimal to Binary Conversion : Since there are only 16 digits in the hexadecimal number system, 4 bits (24=16) are sufficient to represent any hexadecimal digit in binary. In order to convert hexadecimal number into its binary equivalent, the procedure is to convert each hexa- decimal digit to a 4-bit binary equivalent and combine all the resulting binary groups (of 4 digits each) into a single binary number. Table : Binary equivalents of hexadecimal digits 24

Binary to Hexadecimal Conversion : To convert binary into hexadecimal number, the bits of the binary number are grouped into groups of four bits starting at the LSB. Then each group of four bits is converted to its hexadecimal equiv- alent digit. Hexadecimal digits 0 to 9 are equal to decimal values 0 to 9, and hexadecimal digits A to F are equal to decimal values 10 to 15. Hence, here the binary to decimal conversion procedure can be used. But the decimal values 10 to 15 must be represented as hexadecimal A to F. Keywords learned in this chapter Artificial Intelligence Superconductor Parallel processing Data Information Input Unit Output Unit CPU ALU CU Memory Registers Bit Byte RAM SRAM DRAM ROM PROM EPROM EEPROM Auxiliary memory Flash memory Hard dis VDU Hard copy Soft copy Hardware Software Program System software Assembler Interpreter Compiler Utilities Operating system 25

Exercises : 1. Choose the correct option. a. Which of the following is not an output device ? i. Speaker ii. Mouse iii. Printer iv. Monitor b. Which one of the following is the “brain” of a computer ? i. CPU ii. ALU iii. CU iv. MU c. A collection of eight bits is called ______. i. Byte ii. Word iii. Record iv. Nibble d. Second-generation computers were manufactured using which technology ? i. Vacuum tubes ii. Transistors iii. ICs iv. None of these e. Storage of 1KB means the following number of bytes : i. 1000 ii. 1024 iii. 1064 iv. 1012 f. Which of the following is not hardware ? i. Hard disk ii. Printer iii. Assembler iv. CPU g. Fourth generation computers used iii. Microprocessors iv. ICs i. Vacuum tubes ii. Transistors h. Which one of the following is a special-purpose application software ? i. Word-processing software ii. Operating system software iii. Compiler iv. Payroll system i. The base of Octal Number System is___. i. 2 ii. 10 iii.16 iv. 8 j. Who is known as the father of the modern computer ? iv. John Atanasoff i. Charles Babbage ii. Blaise Pascal iii. Herman Hollerith 26

2. Fill in the blanks. a. The first- generation computers used ______ for storage. b. The third- generation computers replaced _______ with ______. c. ________ are high speed temporary storage area. d. ______ is the short form of binary digit. e. A group of four bits is called _____. f. _____ holds data, programs and instructions for computer. g. A microphone is _____ device. h. A _____ is set of instructions to perform a specific task. i. _________ software are used to scan the computers for viruses. j. The decimal system is composed of ____ digits. k. ___________ was the first fully electronic general-purpose computer. l. __________ was one of the first commercially available computers. m. An _______ converts the program written in assembly language into machine language. n. Processing takes place in the _______. o. The ALU performs the _________ and ___________ operations. p. RAM is ___________. q. ROM stores basic _________ instructions to operate the computer. r. _________ memory is an electronic non-volatile storage medium that can be electrically erased and reprogrammed. s. Data and instructions are given to the computer through its _____ device. t. Raw data is processed by the computer to produce _______. u. Results are obtained from the computer through its ________ device. v. 1 MB = _______ KB. w. __________ is an example of primary memory. x. The octal number system uses the digits from _____ to ______. y. A computer system comprise of both _______ and ________. z. _________ represents the set of programs that directs the computer how to work. 3. State true or false. a. Another name for internal memory is primary memory. b. A hard disk can store less data than CD. c. Software represent to the physical components of a computer. 27

d. A projector is input device. e. Interpreter is an utility software. f. The first-generation computers used transistors. g. Atanasoff Berry Computer was the first electronic digital computer. h. IBM 604 is an example of second-generation computers. i. UNIVAC I was one of the first commercially available computers. j. ROM is volatile. k. A group of eight bits is called nibble. l. Computer does not understand any language other than machine language. m. Pen drives use flash memory to store data. n. The monitor is a soft copy output device. o. A compiler translates a program written in machine language into a program written high level language. p. Bit is the smallest unit of data in a computer. 4. Short answer questions a. Who is known as the ‘father of the modern computer’? b. What is a computer? c. Name a popular pointing device. d. Who invented Jacquard’s loom? e. Give the full form of ENIAC and EDVAC. f. Give two examples of second-generation computers. g. What is AI? h. Give two examples of secondary memories. i. What does the CPU do? j. Why we use secondary memory? k. Give two examples of pointing devices? l. Which input device is used to record sound? m. What is the use of barcode reader? n. What is system software? Give two examples. o. What is the role of CU? p. What is the function of ALU? q. What do you understand by memory word? 28

r. What is the function of compiler? s. What is the main limitation of a computer? t. Mention three main features of a computer. u. What is a computer program? v. What are the fundamental components of a computer system? w. What is application software? x. Mention various categories of application software. y. What do you understand by computer memory? z. What is the binary equivalent of hexadecimal 15? 5. Long answer questions a. Mention four features of a computer system. b. Mention the characteristic features of third-generation computers. c. What do you understand by generation of computers ? Mention two disadvantages of first-generation computers. d. Describe the functioning of CPU. e. Draw a block diagram of a computer system. f. What are the categories of printers? Explain. g. What is a bus? Explain three types of buses. h. What are functions of primary storage area? i. Explain three types of ROM. j. What is a purpose of a language processor? Explain the three language processors. k. Differentiate between data and information. l. Write short note on fifth-generation computers. m. What are basic differences between the four generations of computers? n. Write a short note on MARK I. o. Explain the two main types of secondary memory. p. Describe various types of magnetic media. q. Mention some areas where computers are used widely. r. What are the major operations performed by a computer? s. Differentiate between the following pairs: I. Input unit and Output unit II. RAM and ROM 29

III. Soft copy and hard copy IV. Primary memory and secondary memory V. Impact-printer and non-impact printer VI. Assembler and Compiler VII. Hardware and software VIII. System software and application software 6. Carry out the following conversions: 30

2CHAPTER OPERATING SYSTEM AND ITS IMPORTANCE William Henry Gates III (born October 28, 1955) popularly known as Bill Gates is an American business magnate, software developer, and philanthropist. He is the founder of Microsoft Corporation. During his career at Microsoft, Gates held the positions of chairman, chief executive officer (CEO), president and chief software architect. Microsoft Windows Operating System has seen 10 major versions since its release in November 1985.Over 35 years later, Windows looks very different but somehow familiar with elements that have survived the test of time and most recently - a shift from keyboard and mouse to touchscreens. In this chapter, we will learn about what is an operating system, its function and types, some commonly used operating system and operating system directory structure. 31

2.1 WHY TO LEARN OPERATING SYSTEM ? In the Computer System (comprises of Hardware and software), Hardware can only understand machine code (in the form of 0 and 1). So, we need a system which can act as an intermediary and manage all the processes and resources present in the system. An operating system (OS) is a program which acts as an interface between a user and the hardware i.e., all computer resources and controls all components of the computer system. Its main goal is to make the computer system convenient to use. An operating system is a software which performs all the basic tasks like file management, memory management, process management, handling input and output, and controlling pe- ripheral devices such as disk drives and printers. Some popular Operating Systems include Linux Operating System, Windows Operating System,iOS Operating System etc. 2.2 NEED OF AN OPERATING SYSTEM : ¿ OS as a platform for Application programs : Operating system provides a plaform, on top of which, other programs, called application programs can run. These application programs help the users to perform a specific task easily. It is designed in such a manner that it operates, controls and executes various applications on the computer. ¿ Booting : Booting is basically the process of starting the computer. When the CPU is first switched ON it has nothing inside the memory. So, to start the computer, we load the operating system into the main memory. Therefore, loading the OS to the main memory to start the computer is booting. Hence, the OS helps to start the computer when the power is switched ON. ¿ Consistent user interface : Operating System provides the user an easy-to-work user interface, so the user doesn’t have to learn a different user interface every time and can focus on the content and be productive as quickly as possible. ¿ Managing the input/output devices : The OS helps to operate the different input/ output devices. The OS decides which program or process can use which device. Morever, it decides the time for usage. In addition to this, it controls the allocation and deallocation of devices. ¿ Multitasking : Operating System manages memory and allow multiple programs to run in their own space and even communicate with each other through shared memory. Multi tasing gives users a good experience as they can perform several tasks on a computer at a time. 32

¿ Platform for other application software : Users require different application programs to perform specific tasks on the system. The OS manages and controls these applications so that they can work efficiently. In other words, it acts as an interface between the user and the applications. Some other uses for operating system are: ¿ Manages the memory : It helps in managing the main memory of the computer. Moreover, It allocates and deallocates memory to all the applications/tasks. ¿ Manages the system files : It helps to manage files on the system. As we know, all the data on the system is in the form of files. It makes interaction with the files easy. ¿ Provides Security : It keeps the system and applications safe through authorization. Thus,the OS provides security to the system. 2.3 FUNCTIONS OF AN OPERATING SYSTEM The main important functions of an operating system are listed below : n Processor Management : The operating system decides which job should use the processor and for how long. It allocates the processor to a process and de-allocates processor when a process is no longer required. n Memory management : An Operating System keeps track of primary memory, i.e., what part of it are in use by whom and what part are not in use. It decides which process will get memory when and how much. It allocates the memory when a process requests it to do so and de-allocates the memory when a process no longer needs it or has been terminated. n Device Management : An Operating System manages device communication via their respective drivers. It keeps track of all devices and decides which process gets the device when and for how much time. It allocates and de-allocates the device in the efficient way. n Information Management : A computer System works with ‘information’. It stores information, processes information and provides information etc.Thus, managing this information is also an important task performed by an operating system. n File Management : The operating System manages the files, folders and directory systems on a computer. 2.4 TYPES OF OPERATING SYSTEMS „ Batch Processing OS : This type of operating system does not interact with the computer directly. There is an operator which takes similar jobs having the same requirment and groups them into batches. It is the responsibility of the operator to sort jobs with similar needs. Examples are Payroll System, Bank Statements etc. „ Distributed OS : This type of operating system is designed to share its work load over multiple servers (mostly at multiple locations). It shares data and resources among its multiple servers to get maximum efficiency. Examples are Unix, Linux etc. 33

„ Real Time OS : In real time OS, the jobs have fixed deadlines and the jobs have to be completed within their deadlines. The system performance is measured by its ability to complete its jobs within the specified deadlines. Examples are LynxOS, Windows CE etc. „ Interactive OS : Interactive operating systems are computer systems characterized by significant amounts of interaction between humans and the computer. Most users have grown up using Macintosh or Windows computer operating systems, which are prime examples of graphical interactive systems. Games and simulations are interactive systems. „ Time sharing OS : A time sharing operating system allows many users to share the computer resources simultaneously. In other words, time sharing refers to the allocation of computer resources in time slots to several programs simultaneously. The time allowed is extremely small and the users are given the impression that they each have their own CPU and they are the sole owner of the CPU. „ Network OS : These systems run on a server and provide the capability to manage data, users, groups, security, applications, and other networking functions. These types of oper -ating systems allow shared access of files, printers, security, applications, and other net working functions over a small private network. Examples are UNIX, Linux, Mac OS X erc. 2.5 SOME COMMON OPERATING SYSTEMS l Windows : Microsoft created the Windows operating system in the mid-1980s. There have been many different versions of Windows, but the most recent ones are Windows 10 (released in 2015), Windows 8 (2012), Windows 7 (2009), and Windows Vista (2007). Windows comes pre-loaded on most new PCs, which helps to make it the most popular operating system in the world. l Unix : Unix was originally developed in 1969 by a group of AT&T employees Ken Thompson, Dennis Ritchie, Douglas McIlroy, and Joe Ossanna at Bell Labs. The Unix operating system is a set of programs that act as a link between the computer and the user. Several people can use a Unix computer at the same time and therefore it is called a multiuser system. It was originally written in assembly language but was re-written in C language. l Linux : Linux is a family of open-source operating systems, which means they can be modified and distributed by anyone around the world. This is different from proprietary software like Windows, which can only be modified by the company that owns it. The advantages of Linux are that it is free and there are many different versions you can choose from. l macOS : macOS (previously called OS X) is a line of operating systems created by Apple. It comes preloaded on all Macintosh computers, or Macs. Some of the specific versions include Mojave (released in 2018), High Sierra (2017), and Sierra (2016). macOS users account for less than 10% of global operating systems. One reason for this is that Apple computers tend to be more expensive. However, many people do prefer the look and feel of macOS over Windows. l iOS : iOS stands for the iPhone Operating System. It is Apple’s mobile operating system developed and distributed by Apple Inc. It is designed to run on Apple devices like iPhone, 34

iPad, iPod, etc. The first version of Apple iOS was released on 29 July 2007. l Android : Android is a mobile operating system based on a modified version of the Linux kernel and other open-source software, designed primarily for touchscreen mobile devices such as smartphones and tablets.Android has over two billion monthly active users, the largest installed base of any operating system. l BOSS (Bharat Operating System Solutions) : BOSS is an operating system developed by Centre for Development of Advanced Computing (C-DAC), Chennai, in order for enhancing and gain benefit from the usage of Free and Open-Source Software throughout India. BOSS GNU/Linux is an Indian Linux distribution derived from Debian operating system. The latest stable version 8.0 (“Unnati”), was released on 15 October 2019. 2.6 DIFFERENCE BETWEEN 32-BIT AND 64-BIT OPERATING SYSTEMS A 32-bit system can access 232 memory addresses, i.e 4 GB of RAM or physical memory ideally, it can access more than 4 GB of RAM also. A 64-bit system can access 264 memory addresses, i.e actually 18-Quintillion bytes of RAM. 2.7 OS DIRECTORY STRUCTURE A directory is a container that is used to contain folders and file. It organizes files and folders into a hierarchical manner. There are several logical struc- tures of a directory. A File system contains thousands and millions of files, owned by several users. The directory structure organizes these files by keeping entries of all the related files. To get the benefit of different file systems on the different operating systems, A hard disk can be divided into the number of partitions of different sizes. The partitions are also called volumes or mini disks. Each partition must have at least one directory in which, all the files of the partition can be listed. A directory entry is maintained for each file in the directory which stores all the information related to that file. The file entries have information like file name, type, location, the mode in which the file can be accessed by other users in the system. The two important features that must be taken care while maintaining a directory are given below: 35

1. A user must have freedom of giving the desired name to the file, without taking into consideration that the same file names are used by other users on the system. 2. A user must be able to share the files he creates and he must also be able to access the files, created by other users. A directory always has information about the group of related files. Whenever a user or a process request for a file, the file system search for the file’s entry in the directory and when the match is found, it obtains the file’s location from there. There are various types of information which are stored in a directory : Name, Type, Location, Size, Position Protection, Usage etc; 1. Name : – Name is the name of the directory, which is visible to the user. 2. Type : – Type of a directory means what type of directory is present such as single-level directory, two-level directory, etc. 3. Location : – Location is the location of the device where the header of a file is located. 4. Size : – Size means number of words/blocks/bytes in the file. 5. Position : – Position means the position of the next-read pointer and the next-write pointer. 6. Protection : – Protection means access control on the read/write/delete/execute. 7. Usage : – Usage means the time of creation, modification, and access, etc. Keywords learned in this chapter Operating System Multiuser Multitasking Directory 36

Exercises 1. Choose the correct option. a. Which of the following is an operating system ? i. Windows ii. Linux iii. Unix iv. All of these b. Which Operating System is developed by CDAC, Chennai ? i. Windows ii. BOSS iii. Unix iv. None of these c. Which OS has fixed deadlines ? i. Distributed ii. Real-time iii. Interactive iv. Batch Processing d. Name a multiuser Operating system. i. MS-DOS ii. BOSS iii. Unix iv. None of these e. Name a version of macOS. iii. Sierra iv. All of these i. Mojave ii. High Sierra f. In which year was Windows OS released ? i. 1980 ii. 1985 iii. 1983 iv. 1987 2. Fill in the blanks. a. ____________ is the founder of Microsoft Corporation. b. An operating system is a program which acts as an _______ between a user and the hardware. c. The operating system decides which job should use the _______ and for how long. d. A computer System works with __________. e. Windows is an example of _______ operating system. f. Unix was originally developed in _______ by a group of AT&T employees. 3. State True or False. a. Microsoft Windows has 15 versions since its first release in 1985. b. Linux is different from proprietary software like Windows, which can only be modified by the company that owns it. 37

c. iOS is Apple’s mobile operating system. d. The latest version of Android is Unnati. e. Windows comes pre-loaded on most new PCs. f. macOS is Apple’s mobile operating system. 4. Short Answer Questions 1. What is an Operating System? 2. Mention the names of any two commonly used operating system. 3. When was the first version of Apple iOS released? 4. What do you mean by multitasking? 5. What is real-time operating system? 6. What is time sharing and distributive operating system? 5. Long Answer Questions 1. Explain any two functions of an Operating System? 2. Explain any two-operating system used in mobile phones 3. Write a short note on Windows operating system. 4. Write a note on the operating systems created by Apple. 5. What is BOSS? 6. Write a short note on Bill Gates. 7. What is Interactive Operating System? Where is it used? 8. What are the two important features that must be taken care while maintaining a directory? 38

OFFICE 3CHAPTER APPLICATION (MS-WORD, MS-EXCEL, MS-POWERPOINT) “I am not in competition with anyone but myself. My goal is to improve myself continuously.” – Bill Gates In this chapter, we will get a collection of office applications. Each application serves a unique purpose and offers a specific service to its users. It is de- signed to address specific tasks, such as word processing, data management, making presenta- tions and organizing emails. 3.1 WHAT IS A WORD PROCESSOR ? A word processor is a type of software application used for composing, editing, formatting and printing documents. Using word processors, one can modify the documents with the required changes and can print the hard copy when needed. Using these programs, images can also be included in the documents. They provide various tools like spell checker, mail merge, tables etc to provide with a pre- sentable documents. Commonly used word processors are : Microsoft Word, Word Star, OpenOffice. org-Writer, etc. 3.2 FEATURES OF A WORD PROCESSOR Word processing typically implies the presence of text manipulation functions that extend be- yond a basic ability to enter and change text. Let us discuss some of the features: 1. Speed : Typing is easier and quicker in word processing applications. 2. Editing Features : Any types of mistake, if any, are easier to handle in a word processor after typing the documents. If you want to insert, delete or modify some contents, it can be 39

easily done without creating the document again. 3. Formatting Features : Various text formatting options are available which can be used for making the document more attractive like changing font, text colour, alignment, spacing etc. 4. Graphical Features : Pictures, images or graphics are a very useful way of brightening up a document and making it more appealing and interesting for the end user. 5. Storage : Documents can be stored permanently into the storage device for later use. The saved document can be opened, modified and printed anytime. 6. Other useful tools : There are many built – in – tools like spelling and grammar, mail merge, print preview, tables etc. which helps to create a presentable document. 3.3 APPLICATION OF A WORD PROCESSOR Word processors have a variety of uses and applications within the business world, home and education. l Businesses tend to have their own format and style for any documents produced. In Busi- ness word processing is used for: Ü legal copies Ü letters and letterhead Ü memos Ü reference documents l Many homes have word processors on their computers, in the home word processing tends to be educational, planning or business related, dealing with assignments or work being completed at home, or recreational. Examples include: Ü writing short stories Ü letter writing Ü résumé/CV creation Ü card creation l In education word processing is used in a variety of different ways – Ü in the production of assignments, notes and exams 3.4 INTRODUCTION TO MICROSOFT WORD Microsoft Word is a word processing application that runs on a personal desktop, laptop, or mobile computing device. Because word processing tasks are so pervasive in our lives today, you have probably already been using Word. You can use Word to : u Create professional-looking documents that incorporate impressive graphics. u Give documents a consistent look by applying styles and themes that control the font, size, color, and effects of text and the page background. u Store and reuse pre-formatted elements such as cover pages and sidebars. 40