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    1. Components of a PC
      1. Hardware
      2. Processor
      3. Memory
      4. Input/Output Devices
        1. Keyboard
        2. Mouse and its variants
        3. Microphones
        4. Monitor
        5. Sound Systems
        6. Printers
      5. Storage
        1. Hard Disk
        2. Floppy Diskettes
        3. CD-ROMs
        4. Other Storage Devices
         6.    Software
                    1.   System Software
                    2.   Operating System
         7.    Application Software
                   1.    Word Processors
                   2.    Presentation Programs
                   3.    Database Management Software
                   4.    Others

    8.Turning the computer on and off
      Chapter 1.3: Components of a PC system

      Chapter Objective:
      Impart the ability to identify and work with various components of the PC

      As discussed in chapter 1.2, a computer is made up of Hardware and Software. In this chapter we will discuss these two components in detail, so that you are familiar with the functions of these components when you work with computers.

      TOPIC 1.3.1: Hardware

      Topic Objective: To discuss different Hardware components of a PC system

      We have already discussed, in Chapter 1.2, the external appearance of a personal computer appears. Besides these, there is a lot more that constitutes a computer. We will now discuss the important hardware components of a PC in detail.

      As we already know that computers transform raw data into information. This procedure is called processing and to perform this task two components are used: the processor and memory.

      TOPIC 1.3.2: Processor

      It is the most important part of the PC because this is where all the processing takes place. It is like the brain of the computer. It usually consists of one or more microprocessors. Microprocessors are thin chips of silicon or other material consisting of several tiny electronic circuits. Electricity is passed through these circuits to process data. Microprocessors of a computer are also called its central processing unit or CPU. The popular Pentium chip is a type of microprocessor manufactured by Intel corporation.

      The microprocessor is mounted on the computer's motherboard. Motherboard is a flat rectangular card containing the electronic circuits that connect the processor to the other hardware. Motherboard contains special slots to plug in different internal devices such as video cards, sound cards, disk controllers etc.

      The CPU consists of two parts: the control unit and the Arithmetic Logic Unit (ALU). The control unit contains the instructions for the CPU. These instructions are written in the form of computer programs and are carried out sequentially by the control unit. The ALU performs all arithmetic and logical operations.

      The measure of a CPU's processing capability is the speed and accuracy with which these instructions are carried out. The speed of a CPU is measured in MegaHertz (MHz) and it shows the amount of data processed in one operation. The speed of various microprocessors available these days is between 600 MHz and 1700 MHz. Intel manufactures the most popular microprocessors, Pentium and Celeron.

       Back to chapter outline

      TOPIC 1.3.3: Memory

      A computer system requires memory to launch and run programs as well as to store the results of the data processed by the CPU. System memory is of two types: Random Access Memory (RAM) and Read Only Memory (ROM).

      1. Random Access Memory (RAM) - This is the read/write memory of the computer. Data is written to and read from this memory. It is used to store data and application programs. However, RAM is volatile and requires constant supply of power. Whenever the system is turned off, all contents of RAM disappear. This is why it is necessary to frequently save data to a storage device. The amount of RAM in a computer directly affects its speed and power. The measurement unit to describe a computer's memory is the byte. A byte is the amount of memory needed to store a single character (a letter or numeral). To refer to larger amounts of memory, the following units are used:

      Unit Abbreviation Approximate Value in bytes Actual Value in bytes







      1,000,000 (1 million)

      1,048, 576



      1,000,000,000 (1 billion)


      Computers these days usually have 64 to 128 MB memory.

      One unit of Kilobyte - Abbreviation KB - Approximate Value in bytes = 1000 - Actual Value in bytes = 1024

      One unit of Megabyte - Abbreviation MB - Approximate Value in bytes = 1,000,000 [one million] - Actual Value in bytes = 1,048,576.

      One unit of Gigabyte - Abbreviation GB - Approximate Value in bytes = 1,000,000,000 [one billion] - Actual Value in bytes = 1,073,741,824.

      2. Read Only Memory (ROM) - It is the permanent memory of the computer. It stores the instructions required to start up all computer parts while booting. It is non volatile and hence its contents do not disappear.

      Back to chapter outline

      TOPIC 1.3.4: Input/Output Devices

      Computers are useful because they accept data from users and deliver results to users. This interaction with users is possible through various input and output devices.

      1. Input Devices:
      These devices allow users to enter data and instructions. Some of the most common input devices are:

      A. Keyboard

      It is a typewriter- like device, with about 100 keys, that comes as part of the standard equipment with a computer. It allows the users to enter letters, numbers, and commands. The keys of a normal keyboard are classified under the following categories;

      1. Alphanumeric Keys - These are similar to those found on a typewriter and include letters, numbers, mathematical and punctuation symbols. There are certain other keys, viz, tab, caps lock, backspace and enter.

      2. Modifier Keys - These keys are used to modify or edit already entered data. These keys are Shift, Ctrl and Alt.

      3. Function Keys - These are usually found on the topmost row of the keyboard and allow the users to input commands with the press of one key. Each function key represents a specific command, but that depends on the program being used by the users.

      4. Numeric Keypad - These are found on the right hand side of the keyboard, and look like a calculator. Besides keys for numbers and mathematical symbols, there is a 'Num Lock' key, which when pressed activates the number keys.

      5. Cursor movement Keys - Cursor denotes your location on the screen. Cursor control keys help users to move around on the screen. These include the arrow keys - for up, down and sideward movements; Home key - to move to the beginning of a line; End key- to move to the end of a line; Page Up key - to jump to previous page; and Page down key - to jump to the next page.

      6. Special purpose Keys - For specialized functions there are keys, viz - Insert, Delete, Esc, Print Screen, Scroll Lock, Pause, Start and Shortcut.

      Instructor link: Classroom activity on keyboard

      B. Mouse and its variants

      Besides keyboard, mouse is another device that comes as part of the standard equipment when you buy a PC. Mouse is used as a pointing device, i.e. it allows you to move the cursor anywhere on the screen. It is used to select text, access menus, and draw graphics. Though it is not a welcoming thought for many, but this device actually looks like the back of a hunched white mouse. It is designed to fit within the grip of your palm. The most popular models a trackball at its base and two or three buttons where your fingers will be placed when you grip it. There are various models and variations of the mouse. These include:

      1. Trackball - In this design, instead of the base, the trackball is also on the top so that the users thumb rests on the ball, and the fingers are on the button.

      2. Trackpad - In Notebook computers, instead of a mouse there is a built-in touch sensitive small square pad. The movement of finger across this pad translates into pointer movement on the screen. There are two or three buttons which work exactly like the mouse buttons.

      3. Pointer - In some notebooks, instead of the touchpad, there is a small joystick like knob in the keyboard itself. This is knob or pointer, can be moved in any direction to move the pointer on the screen. There are two or three buttons which work exactly like the mouse buttons

      Instructor link: Classroom activity on mouse

      C. Microphone

      It is usually a long, slender, and cylindrical device with a bend and a base on which it can stand. Microphones are used to input your voice into a computer, for various purposes such as internet telephony, voice chat over the internet, or speech commands to operate your computer. Back to chapter outline

      2. Output devices:

      These devices deliver processed data back to the users. Some of the most common output devices are:

      A. Monitor - A monitor gives visual display of text, graphics and animations. These visuals or images are made up of tiny dots called pixels. The number of pixels on the screen make up the resolution of an image. The most common type of monitor used for desktop computing is called CRT (Cathode Ray Tube) monitor. It is a device similar to the television - it has a display screen towards the front, with a box towards the rear that contain electrical components of the monitor. It comes with a power button on the front side to turn the screen on or off.

      Monitors come in various sizes from 14 - inches to 21 inches; various resolution setting options such as 640 X 480 (640 pixels horizontally by 480 pixels vertically), 800 X 600, 1024 X 768, 1152 X 864, and 1280 X 1024; and in two types - CRT display and Flat screen display.

      B. Sound Systems - A desktop computer can provide audio output also. The sound system of a computer is controlled by a device called sound card. The sound card converts digital sounds into electric current, which is then passed on to the speakers. Sound cards can do the reverse also, that is convert external sounds into digital sounds.

      Speakers attached to these systems are similar to those coming with small stereos. In some models, the monitor has built in speakers, but usually the users need to attach external speakers.

      C. Printer - Printers are output devices used to produce copies of electronic documents on a paper. Printers are categorized into impact printers and non-impact printers. Impact Printers create images by pressing an inked ribbon against the paper, and using pins to shape the image. The most popular impact printer is a dot matrix printer that forms characters by creating a series of dots.

      Non-impact printers use different methods to create images. There are Inkjet printers that use a minute nozzle to spray ink on papers, while Laser printers use heat to bind microscopic ink particles on specific parts of a paper. There are printers available for taking output in Braille also.

      TOPIC 1.3.5: Storage

      We now know how processors, memory, input and output devices are essential for the functioning of a computer. However, there is another component that is equally important for the useful functioning of a computer. This is storage media. It is basically space where computer program files and electronic documents are kept.

      The following three points distinguish storage from memory:

      1. It has more space than memory

      2. It retains its contents when computer is switched off, while contents in memory disappear.

      3. It is slower than memory.

      The most commonly used storage medium is a magnetic disk. A magnetic disk is round and flat, and it spins around its center. It has read/write heads, similar to the head in a tape recorder, which are used to read data from the disk or write data on to it. While in use disks are held by devices called disk drives. Most PCs come with built-in non-removable disk called the hard disk or hard drive. Most computers come with hard disks with capacities ranging from 6 GB to 40 GB of memory space. Hard disks are the used as the primary medium for storage.

      Most PCs also come with a diskette drive, which allows the usage of removable diskettes called Floppy disks. Floppy disks have a plastic or vinyl cover that is square-shaped and they contain a circular magnetic strip on which data is stored. The most common floppy disks in use these days are 3.5-inch diskettes with a storage capacity of 1.44 MB. These are used to move files of programs or electronic documents between computers; loading new programs into a computer system, or as a back-up storage for programs or electronic documents. You can add data to and delete from a floppy disk.

      Instructor link: Classroom activity on floppy disk

      Lately, CD-ROMs (Compact Disks - Read Only Memory) have become very popular as storage devices. These are flat, round, about 4.5 inch in diameter and with a hole in between to hold them. These fall under optical storage devices because data is stored on a reflective surface which is then read by a beam of laser light. CD-ROMs can usually store 74 minutes of audio or 650 MB of data, about 450 times of what a floppy disk can store, and the data stored on a CD-ROM cannot be changed. A CD-ROM drive is required to read data from an already recorded CD-ROM. However to write data on a CD-ROM a different type of drive called CD-Recordable (CD-R) drive, and a special disk called CD-Rewritable disk is required.

      Instructor link: Classroom activity on CD-ROM

       Back to chapter outline

      Topic Exercises

      A. Complete the following sentences:

      1. Microprocessors are also called as _____.
      2. The actual value of a kilobyte is _____  bytes.
      3. Printers are categorised into _____ printers and _____ printers.
      4. The speed of CPU is measured in _____.
      5. Most used storage devices are _____ disk, _____ disks, and CD-ROMs.
      B. What is the difference between memory and storage?

      C. Explain the following terms

      1. Byte
      2. Cursor
      3. Processing
      4. Booting
      5. ROM
      D. What is a Motherboard?

      E. What is the function of the control unit and the ALU?

      F. List three output devices and three input devices.

      Back to Chapter Outline

      TOPIC 1.3.6: Software

      Topic Objective: To discuss different types of Software and their functions in a PC system

      A PC is so designed that it can perform different tasks. So, you can write a document, play an audio CD, send and receive emails, edit photographs and much more on the same computer. The hardware components of a computer, discussed in Topic 1.3.1, provide the infrastructure required to perform these tasks. It is the Software that enables a computer to perform a specific task. Software is a set of electronic instructions, called programs, which tell the hardware components what to do. Therefore, software provides the computer a direction and purpose to its functioning.

      When a computer is using a particular program, it is said to be running or executing the program. Software is classified into two types of categories based on their purpose, these categories are - system software and application software.

      1. System software - System software instructs the computer about how to interact with the user, how to use various hardware devices attached to it, how to run other software programs. Some of the system software programs are operating system, compilers, and sorting programs. We will discuss operating system in greater detail.

      2. Operating System - Operating system is the master control program of the computer. It translates the commands given by the user into codes that can be used by the computer, and then send the result of the processing done by the computer for output. Therefore, the functions performed by operating system are:

      1. Coordinate the functioning of programs with CPU, memory, input devices, output devices, and other hardware and software.
      2. Run programs, like word processors, by loading them into the memory so that users can start working on these programs.
      3. Provide instructions to display on-screen elements, which are called the user interface.
      4. Manage storing and retrieval of information from storage storage devices.
      Some of the most commonly used operating systems are DOS, Macintosh, Windows 95, Windows 98, Windows 2000, and UNIX. Windows are the most popular operating systems and we will learn the basics of this operating system in this course.

      Back to Chapter Outline

      TOPIC 1.3.7: Application software

      This software directs the computer to perform specific tasks for the user. For example, there are specific programs for word processing, calculations, making drawings, or editing images. We will briefly discuss some of the categories of application software.

      1. Word Processing Software - is also known as a word processor. It provides tools to users for creating and editing text-based documents. Word processors allow inclusion of tables, images, sounds, and video to documents. The advanced word processors even check spellings and grammar, automatically. Most popular word processors are Microsoft Word or MS-Word and Wordpad.
      2. Spreadsheet Software - This software is used for entering, calculating, and analysing sets of numerical information. These are used for variety of purposes from preparing and maintaining corporate budgets to financial resource planning. Spreadsheets allow text, numbers, images, graphs and charts. Most popular spreadsheets are Microsoft Excel, Lotus 1-2-3.
      3. Presentation Software  - These programs allow the user to create and edit colorful presentations that can be displayed to an audience in different ways. This software allows users to develop a series of single-screen images called slides, which contain text, numbers, and graphics. These are widely used by business executives to present information to a group of people, such as investors, seniors, colleagues, employees, or customers. Most popular presentation program is Microsoft PowerPoint.
      4. Database Software  - These programs are used for storing, retrieving and processing large amount of data. This could be anything from someone's address book to a mailing list to a daily log of technicians in a company. The repository of such data is called a database. A database management software allows adding new information, searching through previously stored data, printing out records, and conducting certain other programmed functions. One of the more popular database management programs is Microsoft Access.
      5. Other application programs  - There are innumerable application programs in use today by millions of computer users. It really depends on the type of work the user wants to do. So there are

        • Graphics software used to create and edit images in several different formats.
        • Multimedia authoring software to develop audio-visual presentations. These include audio commentaries, animation, simple games, or digital movies.
        • Entertainment and education software programs that use multimedia presentations to offer engaging animations, films, lessons, or self-help tutorials.
        • Web design tools help programmers develop documents that can be published on the Internet. Web browsers allow users to access web pages on the Internet. There are several Internet applications in use and many are being introduced as the Internet matures.
        • Networking and communication software allow users to connect with other computer users either on small networks, large corporate networks or on the Internet.

        Topic Exercises

        1. What is software? 2. The two categories of Software are _____ software and _____ software.

        3. List three system programs and three application programs.

        4. What are the four functions of a system software?

        5. The software that directs the user to do a specific task is _____ software.

        6. What is the purpose of a Database software program?

        7. When a computer is using a particular program, it is said to be _____ or executing it.

        8. Name two most popular Word processors and Spreadsheet programs.

        9. List three most common operating systems.

        10. What is the use of a web browser?

        Back to chapter outline 

        TOPIC 1.3.8: Turning a computer on and off

        Topic Objective: Teach the first step in using computers

        It is a simple and easy operation to turn a computer's power on and off. However, there is a particular way in which it should be done, otherwise you might damage the components of your computer.

        A. Turning it on

        Before turning on the computer, ensure that all necessary cables are connected appropriately to the system unit. Also, ensure that there is no floppy disk in the floppy diskette drive. Now follow the following steps:

        1. Your computer must be connected to a switch box from which it gets the power. Put this switch in the ON position.
        2. If you are using a stabilizer or UPS, turn its switch in ON position. Also, keep the other devices, such as Monitor and printer, also switched on.
        3. Now find the power button in the front part of the system unit, and push it once. A light on the system unit will glow indicating that the system has been switched on successfully. There will be a whirring sound to indicate that the system is booting up.
        4. It will take a few minutes for the compute to complete the start-up process. At the end of this process Windows desktop will appear on the screen.

        B. Turning it off

        It is important to shut down the system properly, especially in Windows based systems. This is because Windows creates many temporary files on the computer's hard disk, while you are running an application. By shutting properly, the computer erases these temporary files properly. To turn off the computer follow the following steps:

        1. Close all applications that might be running on the computer screen and then remove any disks from floppy diskette drive or CD-ROM drive.

        2. Now on the bottom left of the screen there is a 'Start' button. Click on this button. To do so, you may use the mouse by moving the screen pointer on the Start button and then click the left button of the mouse (left-click). Alternatively, you may use the 'Start' key on your keyboard.

        User Tip: Start Key

        3. 'Start' menu will appear immediately on clicking the 'Start' button. On this menu there will be a list of options. The first option from the bottom is 'Shut Down'. Click this option. To do so, you may use the mouse by moving the screen pointer on the 'Shut Down' option and then left-click over it. Alternatively, after the Start menu appears you may click the 'U' key on the keyboard.

        4. The shut down windows dialog box will appear. This dialog box asks you the task you want to perform. There will be four options to select from - Stand by, Shut Down, Restart, and Restart in MS-DOS mode. The Shut Down option will appear automatically selected. There will be three buttons on this dialog box, labeled OK, Cancel and Help.

        5. Now, click the 'OK' button. You can use the mouse to do so, by moving it over the 'OK' button and then left- click over it. If you are using the keyboard, press the 'Tab' key on the keyboard once, and then click the 'Enter' key.

        User Tip: Tab Key

        6. Windows will begin the shut down process. The following message will be displayed on the screen - 'Windows is shutting down'. When the process is completed, the following message will be displayed 'It is now safe to turn off your computer'. When this message appears, turn off the computer by pushing the power button at the front of the system unit.

        Topic Exercises

        1. Why is it important to shut down a computer properly, especially Windows-based computer?
        2. What is the indication that the system is booting up?
        3. What message would the computer display after the shutting down process is completed?
        4. Which button do you have to press to start the computer?
        5. The four options that appear in the shut down dialog box are Shut down, _____,_____, and _____.

        Back to chapter outline

        Term Explanation


        Whenever computer is switched on it is called booting the computer.

        Back to text

        Sound Card

        The sound card is a flat and thin card that is mounted on the motherboard and it converts external sounds into digital sounds, and digital sounds into electric current which is then passed on to the speakers.

        Back to text

        Video Card

        The video card is a flat and thin card that is mounted on the motherboard and it converts external images into digital images, and digital images into electric current which is then passed on to the monitor.

        Back to text

        Classroom Activities


        The instructor may explain the operation of all the keys on a keyboard in detail and ask the students to operate the same under supervision.

        Back to text


        The instructor may explain the various operations of a mouse in detail and ask the students to operate the same under supervision.

        Back to text

        Floppy Disk

        The instructor may open a used floppy disk to explain the various parts of a floppy to the students.

        Back to text


        The instructor may explain to the students a CD-ROM while students touch and feel it.

        Back to text

        User Tip

        Start Key

        'Start' Key is the second key from left, on the first row from bottom, on the alphanumeric part of your keyboard.

        Back to text

        Tab Key

        Tab key is the first key from the left, in the third row of keys from the top of the keyboard.

        Back to text

        Back to Chapter Outline

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