CCC, 'O' Level E-book Notes for preparation | Basic Computer Course Part 1 - Knowing Computer


What is Computer System?

  • A computer system is an electronic data processing device which can read and write, compute and compare, store and process large volume of data with high speed, accuracy and reliability.
  • A computer system has several components like Keyboard, Mouse, Processor, Memory, Monitor etc.
  • The basic Organization of a computer system includes the following:
    • Input Unit: The data is entered using an input device such as a Keyboard or a Mouse.
    • Processing Unit: The computer system processes the data according to a set of instructions called Program.
    • Output: The computer system returns the processed information in the form of output that can either be printed or displayed on the output devices like Printer or Monitor.
    • Memory: The computer system saves the data and the instructions in the memory for further retrieval.

Basic Applications of Computer System

  • Computers systems have a wide range of use in almost every field of our life.
  • They are specially used in the following fields:
    • Office Use
      • The work done in offices is mostly the preparation of letters, reports, memoranda, copy of advertisement, publicity, minutes, contracts, forms, notes etc.
      • This can be done through computer system in most efficient manner.
    • Data analysis
      • You can analyze the data through special software called spreadsheet programs.
      • You can also prepare the product sales, profits and investment reports.
      • You can also sort, merge and manipulate data (as needed) by accepting the data from other files.
    • Accounting and Investment Analysis
      • Accounting Programs are used for data entry, billing, inventory control, Sales Analysis.
      • Softxware packages for such analysis are available at a nominal price. Example: MS-Office Suite supported by Microsoft Corporation.
    • Graphics and Animation
      • Computers system can be used to make drawings, graphics and movies.
      • CorelDraw, Illustrator, Visio 2000 and Free Lance plus for Windows are some such software packages, which can help you in increasing your drawing capability.
    • Education
      • In educational institutions computers system are used as teaching aid, research tool and analyzing system.
      • When computer system is used as a teaching and learning aid it is referred to as computer-assisted instruction (CAI) or Computer Assisted Learning (CAL).
    • Banks
      • Banks use computer systems to provide online service to customers and to answer customer queries regarding their bank balance etc.
      • To handle cash, banks use cash dispensing machines (Asynchronous Transfer Mode (ATM)).
      • With the use of computer systems, electronic transfer of funds from one account to another has become possible.
    • Airlines and Railway Ticket Reservation
      • Indian Railways have computerized ticket reservation in almost all important railway stations.
      • The computer system stores all necessary information required for ticket processing such as
      • Train number,
      • Stations,
      • Distance between stations,
      • Number of seats available in each train for each class,
      • Train fare etc.
    • The computer system can also give information regarding train timings, fares etc. On telephone enquiry.
    • E-mailing
      • Electronic mail (E-mail) is a system whereby through computer system users can exchange messages, greetings etc. with each other via Internet, at a very cheap rate.
      • E-mail allows you to create, send, receive and store messages.
      • You can send mail to individuals or groups with a single click.

Components of Computer System

  • The main components of a computer system are:
    • Central Processing Unit.
    • Input Devices/media.
    • Output Devices/media.
  • Some special purpose devices and media are also available.

Central Processing Unit

  • The CPU is also called the brain of the computer system.
  • Its basic function is to perform calculations and various logical operations.
  • It consists of three parts:-
    • Control Unit
    • Arithmetic and Logic Unit (ALU)
    • Memory or Storage

Control Unit

  • Consists of electronic circuits.
  • Selects, interprets and executes instructions.
  • Governs input/output (I/O) operations,
  • Data transfer to and from storage and
  • Guides the routing of data between storage location and the arithmetic logic unit.

Arithmetic and Logic Unit (ALU)

  • Comprises of electronic circuits.
  • Performs calculations and comparisons.
  • Works at tremendous speed and executes millions of instructions per second (MIPS).

Memory or Storage

  • Also called internal storage or main memory or random access memory (RAM).
  • Consists of very fast memories like magnetic core memory or semiconductor memory.
  • Stores program instructions or part of data for immediate need.
  • Data is stored in a computer system memory in the form of words, bytes and bits.


  • Keyboard is an input device.
  • Computer system keyboard is an electromechanical component designed to create special standardized electronic codes when a key is pressed.
  • Keyboards come in a variety of sizes and shapes.
  • Most keyboards having a number of features in common:
    • Standard Typewriter keys.
    • Function keys.
    • Special purpose keys.
    • Cursor Movement keys 5. Numeric keys.


  • The mouse is also an input device that is much in use in graphics as well as when working with a GUI (Graphic User Interface).
  • When a mouse is slid across a flat surface, the screen cursor also moves in the direction of the movement of the mouse.
  • With a click of the button, the system can be notified of the selected position.


  • Visual Display Unit is the most popular I/O device used nowadays for interactive processing.
  • A keyboard is used to enter data into a processor and a Video Display Unit, called Monitor.
  • It is used to display the keyed in data.
  • It also receives received processed information and messages from the computer system.

Other Input/Output devices

Other Input devices: MICR

  • Magnetic ink character recognition devices were developed to assist the banking industry.
  • It is used in the processing of cheques.
  • The most commonly used character set by MICR devices is known as E13B font that consists of numerals 0-9, and 4 special characters.


  • These are basically input devices that are capable of recognizing marks or characters.
  • They are used for direct entry of data into the computer system.
  • Different types of scanners are:
    • OCR,
    • OMR,
    • Bar Code Reader,
    • Desk scanning.

Optical Character Reader (OCR)

  • These are scanner devices that are capable of detecting alphabetic and numeric characters by comparing the shapes with internally stored patterns.
  • These are expensive and are used only for large-volume processing applications e.g. by credit-card companies.


  • These scanners are capable of recognizing a pre-specified type of mark made by a pencil.
  • These are normally used for validation of input documents, evaluating answer-sheets in objective-type tests e.g. GRE, GMAT.

Bar Code Reader

  • Data coded in the form of light and dark lines or bars are known as bar codes.
  • Bar codes are used particularly by the retail trade for labeling goods.
  • Bar code reader is a device used for reading bar code data which is performed by laser beam scanner which is linked to a computer system.

Desk Scanning

  • The scanning process involves application of the light source to the image.
  • The light is reflected back form the image into the scanner optics where the varying levels of light are interpreted.
  • The image is then reconstructed digitally and displayed on the screen.

Touch Screen

  • It is a computer system screen designed or modified to recognize the location of a touch on its surface.
  • By touching the screen, the user can make a selection or move a cursor.
  • The simplest type of touch screen is made up of a grid of sensing lines, which determine the location of a touch by matching vertical and horizontal contacts.

Light Pen

  • A light pen is a pointing device.
  • It is used to select a displayed menu option on the monitor.
  • It is a photosensitive pen like device.
  • It is capable of sensing a position on the CRT screen when its tip touches the screen.

Other Output devices: Printers

  • Printers are primary output devices used to prepare permanent documents for human use.
  • Printers are classified as:
    • Impact printers.
      • Letter Quality Printer.
      • Line Printer.
    • Non-Impact printers.

Impact Printers

  • These operate like a typewriter, pressing a typeface against paper and inked ribbon.
  • E.g. daisy-wheel printer, dot-matrix printer.
  • Letter Quality Printer:
    • These are also called character printers or serial printers because they print one character at a time.
    • They produce a very high quality print image (one that is very clear and precise) because the entire character is formed with a single impact such as a Daisy Wheel Printer or a Dot Matrix Printer.
  • Line printers
    • These are high speed printers, which cater to huge volumes of output requirements of large computer system organizations.
    • These are known as Line printers because they use impact methods to produce one line at-a-time printed output. E.g. chain printer, band printer, drum printer.

Non-Impact Printers

  • These printers use thermal, electrostatic, chemical and inkjet technologies.
  • Thermal Printers
    • These printers use heat to produce an image on special paper.
    • No ribbon or ink is involved. For users who want the highest-quality desktop color printing, thermal printers are the answer.
    • The print mechanism, is designed to heat the surface of chemically treated paper so that a dot is produced based on the reaction of the chemical to the heat.
  • Ink Jet printer.
    • The ink jet printer ejects a steady stream of ink drop towards the printed page.
    • The drops are selectively discarded by electrostatic attraction to leave only those that are needed to form the desired symbol.
    • Those that are not needed are captured in a tiny gutter & filtered to remove impurities.
    • They are then re-circulated through the drop-generating mechanism.
  • Laser Printer
    • This printer is much less mechanical than impact printer (that is, no print heads move, no print hammers hit). resulting in much higher speeds and quieter operation.
    • The process resembles the operation of a photocopy machine.
    • The major advantages of laser printers are:
      • Very high speed.
      • Low noise level.
      • Low maintenance requirements.
      • Very high image quality.
      • Excellent graphics capabilities.

Display Devices

  • This is one of the most important Peripheral devices in the computer system.
  • The following different kinds of display devices are available:
    • Liquid crystal Display(LCD):
      • Earlier LCDs were used commonly in watches and clocks.
      • But nowadays LCD technology is used to manufacture LCD display devices for computer systems.
      • The major advantage of LCD is the low energy consumption.
      • They also have color capability but the image quality is relatively poor.
    • Projection Displays
      • A large screen upon which images are projected replaces a personal size of the previous displays.
      • These systems can be connected to computer system and whatever appears on the computer system terminal gets enlarged and projected on a large screen.
      • Another method is to connect a computer system to an LCD Flat screen and to project the LCD Image using Overhead projector.
      • These are popularly used for seminars, classroom lectures and presentations etc.

Memory Location

  • Memory of the computer system is divided into small parts called locations.
  • Each location has a unique address.
  • Location is further subdivided into bits.
  • Different computer systems have a different location size varying from 8 to 64 bits.

Computer Memory

  • Bit
    • Bit stands for one binary digit, which is either 0 or 1.
  • Byte
    • Number of consecutive bits combines to make a byte.
    • Most commonly used combination is of 8 bits.
    • Size of main memory is given in Kilobytes (KB), Megabytes (MB) and Gigabytes (GB).
    • Primary Storage / Internal Memory / Main Memory.
    • The main memory, also called random access memory (RAM) is the work area of the computer system.
    • It stores program instructions or part of data for immediate needs.
    • The storage capacity of RAM is limited.
    • A typical modern computer system can have a RAM size of 32MB or 64MB or greater up to 8GB or more.
    • It is volatile memory of the computer system and when the power goes, the contents stored in RAM are lost.
    • RAM can be classified as DRAM (Dynamic RAM) or SRAM (Static RAM).
    • SRAM (Static RAM):
      • SRAM (static RAM) is random access memory (RAM) that retains data bits in its memory as long as power is being supplied.
      • Unlike dynamic RAM (DRAM), which stores bits in cells consisting of a capacitor and a transistor, SRAM does not have to be periodically refreshed.
      • Static RAM provides faster access to data and is more expensive than DRAM. SRAM is used for a computer’s cache memory and as part of the random access memory digital-to-analog converter on a video card.
    • DRAM:
      • Dynamic random access memory (DRAM) is the most common kind of random access memory (RAM) for personal computers and workstations.
      • The network of electrically-charged points in which a computer stores quickly accessible data in the form of 0s and 1s is called memory.
      • Random access means that the PC processor can access any part of the memory directly rather than having to proceed sequentially from some starting place.
      • DRAM is dynamic in that, unlike static RAM (SRAM), it needs to have its storage cells refreshed or given a new electronic charge every few milliseconds.
      • Static RAM does not need refreshing because it operates on the principle of moving current that is switched in one of two directions rather than a storage cell that holds a charge in place. Static RAM is generally used for cache memory, which can be accessed more quickly than DRAM.

Secondary Storage

  • The secondary storage devices are used to store programs and data on a permanent basis.
  • Their storage capacity is much higher compared to main memory of the computer system.
  • Secondary Storage devices accept data or program instructions from the processor retain them and then write them back to the processor as and when needed.
  • The examples of secondary storage devices are Hard Disk, Magnetic tapes, and Pen drives etc.
  • Hard Disk
    • These are specific kind of storage devices that cannot be removed and are fixed inside the computer system.
    • That is why these are also called as fixed disks and store programs permanently.
    • The storage capacities of the disks that are used these days are having Gigabytes of storage and these are faster in comparison to Floppy disks.
  • Magnetic Tape
    • This is also a magnetic media which stores data sequentially in them.
    • Though they provide unlimited storage capacity they suffer from a very serious problem.
    • Since the data stored in them is sequential in nature, retrieval of data takes a very long time.
    • These are used for archival backup storage.
  • CD-ROM
    • Compact disk, read-only memory optical disks have a very large storage density and the access time is relatively low.
  • Digital Versatile Disc
    • Digital Versatile Disk is in genre of optical discs with same overall dimension of CDs but much higher capacity.
    • These can store at least 7 times more data than CD ROM.
    • Static Memory and Memory Sticks.
    • Also commonly known as pen drive or jump drive or flash drive.
    • Static memory devices use memory chips to store information.
    • This information is retained even after power is turned off.
    • They connect to a USB port on the computer system and offer capacities of 128 MB or more.
    • Due to their size and shape, these devices are known as USB memory keys or flash drives and have widely replaced floppy disks for transportation of files between systems.
    • Many portable and hand-held devices rely entirely on static memory for storage.

Semiconductor Memory

  • These days, internal memory consists of extremely small bit storage circuits (flip-flops) etched on a silicon chip.
  • All the electronic elements to store a bit are placed in such a small area of the chip that a single chip can store millions of bits.
  • The individual chips are arranged in groups to form a memory module.

Types of Semiconductor Memory - Random Access Memory (RAM)

  • Any information can be read from and written into a RAM.
  • It is a read/write memory.
  • It is a volatile memory i.e. its contents are lost if the power supply is interrupted or turned off.
  • The main memory of the computer system is RAM.

Read Only Memory (ROM)

  • It is thus completely non-volatile.
  • ROM is permanently programmed with information during manufacture, by implementing the appropriate pattern of two state values.
  • It cannot be changed subsequently by a normal write operation.
  • It is mainly used to hold those programs, which are required permanently.

Cache Memory

  • It is a small capacity high-speed memory used to make processing faster.
  • The main memory can process information very fast, but it takes much longer to transfer data to and from the input/output devices.
  • The cache memory compensates for this mismatch in operating speeds.
  • It holds those parts of data and the active program, which are most frequently used.
  • Thus, the performance rate of the CPU improves.

Concept of Hardware and Sofware


  • Hardware refers to the physical components of a data processing system.
  • Input, storage, processing and control devices are hardware such as Hard disk, Printer, Keyboard etc.
  • Without any hardware your computer system would not exist and software would have nothing to run on.
  • Computer system software is something that executes within the hardware.
  • The hardware of a computer system is infrequently changed, in comparison with software and data.
  • Hardware professionals deal with the manufacturing and maintenance of computers system.
  • Many manufacturers mass produce computer systems and sell them either through direct marketing or retail chains.
  • There are also a number of vendors that can custom assemble computer systems to the end-user′s specifications.
  • It is also possible to purchase the individual parts and component of a computer system and build it.
  • Some of the items to consider when purchasing a computer system include:
    • The motherboard.
    • Processor.
    • RAM.
    • Storage.
    • Adapter cards.
    • Power options.


  • A computer system can only do what a programmer asks it to do.
  • To perform a particular task the programmer writes a sequence of instructions, called the program.
  • An instruction is a command given to the computer system to perform a certain specified operation on the given data.
  • A set of programs written for a computer system is called software.
  • Without software, hardware is of no use.
  • It cannot produce any results on its own.
  • It is a general term used to describe a collection of computer system programs, procedures and documentation that perform some task on a computer system.
  • Usually written in high-level programming languages software are easier and more efficient for humans to use (closer to natural language) than machine language.
  • High-level languages are compiled or interpreted into machine language object code.
  • Software engineers (programmers, systems analysts) develop and maintain software.
  • With technological changes, software changes take place faster than hardware changes.
  • Practical computer systems divide software systems into two major classes:
    • Application Software.
    • System software.

Application Software

  • Software that allows you to do things like create text documents, play games, listen to music, or surf the web is called application software.
  • In general, application programs are software that enable the end-user to perform specific, productive tasks, such as word processing or image manipulation.

Systems Software

  • Systems software comprises of an Operating System and all utility programs (like Compiler, Loader, Linker, and Debugger) that manage computer system resources at a low level.
  • Operating systems, such as GNU, Microsoft Windows, Mac OS X or Linux, are prominent examples of system software.
  • System software is software that basically allows the parts of a computer system to work together.
  • Without the system software the computer system cannot operate as a single unit.
  • System software performs tasks like transferring data from memory to disk, or rendering text onto a display device.

Data and information

  • In general, raw data that has been verified to be accurate and timely, is specific and organized for a purpose, is presented within a context that gives it meaning and relevance.
  • And which leads to increase in understanding and decrease in uncertainty.


  • Collection of facts.
  • Raw Information.
    • Processing.
    • Sequence of actions required to be performed on data to convert it into results.
    • For example, a merit list is generated after processing the raw information available about the marks of each student.
    • Results.
    • Useful Information.
    • Facts in organized manner.
  • The computer system is an electronic data processing device.
  • It is capable of taking input, processing it to generate useful information (output) and store both input as well as the output.
  • The data processing cycle comprises of following 4 distinct stages viz. :-
    • Input: Data is collected and entered into the computer system. This is called input process.
    • Storage: What is entered into the computer system is stored in its main memory.
    • This storage is temporary i.e. the contents of the memory are lost when the power is switched off.
    • Another memory, called secondary memory, is used to store the information of the main memory permanently.

Processing & Output

  • Processing :
    • The sequence of actions that are performed on the data stored in the main memory, to get results is called processing.
    • Results are stored in the main memory till they are transferred to an output device.
  • Output:
    • Stored results are taken out of the main memory.
    • This process is known as output process.

Applications of IECT

  • IECT or Information, Electronics and Communication Technology are used in various sectors.
  • IECT can be used to generate quality manpower.
  • Example of some of the sectors are
    • e-Governance,
    • Entertainment Multimedia and
    • Education etc.,


  • e-Governance is a key to make information technology (IT) relevant to ordinary citizens.
  • It allows citizens to communicate with Government and participate in the Governments′ policy-making.
  • It is a network of organizations to include Government, nonprofit and private-sector entities.
  • In e-Governance, there are no distinct boundaries.
  • The model for e-Governance is a one-stop portal, such as, where citizens have access to a variety of information and services.
  • An ideal portal would be one for employment where a citizen creates a profile and is presented with employment opportunities at the federal, state, local, non-profit and private-sectors.
  • The primary delivery models of e-Governance can be divided into:
    • Government-to-Citizen or Government-to-Customer (G2C).
    • Government-to-Business (G2B).
    • Government-to-Government (G2G).
    • Government-to-Employees (G2E).
  • Within each of these interaction domains, four kinds of activities take place:
    • Pushing information over the Internet e.g.: regulatory services, general holidays, public hearing schedules, issue briefs, notifications etc.
    • Two-way communications between the agency and the citizen, a business, or another Government agency.
    • In this model, users can engage in dialogue with agencies and post problems, comments or requests to the agency.
    • Conducting transactions e.g.: lodging tax returns, applying for services and grants.
    • Governance e.g.: online polling, voting and campaigning.
    • The primary delivery models of E-Government are classified depending on who benefits.
    • In the development of public sector or private sector portals and platforms, a system is created that benefits all constituents.
    • Citizens needing to renew their vehicle registration have a convenient way to accomplish it while already engaged in meeting the regulatory inspection requirement.
    • To develop these public sector portals or platforms, Governments have the choice to internally develop and manage, outsource or sign a self-funding contract.
    • The self-funding model creates portals that pay for themselves through convenience fees for certain e-Government transactions, known as self-funding portals.

Entertainment Multimedia

  • Multimedia is a combination of sound and images with text and graphics.
  • This would include movies, animations, music, people talking, sound effects like the roar of a crowd and smashing glass.
  • The field of entertainment uses multimedia extensively.
  • One of the earliest applications of multimedia was for games.
  • Multimedia made possible innovative and interactive games that greatly enhanced the learning experience.
  • Games could come alive with sounds and animated graphics.

Sound Input

  • Recording sounds for your computer system requires special equipment.
  • Microphones can capture sounds from the air, which is good for sound effects or voices.

Voice Input

  • Talking data into the computer system when your hands and eyes are busy should certainly be more efficient.
  • You can tell the computer system what to do instead of typing commands, like saying "Save file".
  • One has to be careful enough while giving the sound input with regard to pronunciation of words.
  • Also there could be a problem that dictionary of understood words does not include some of the more "forceful" words.

Video Input

  • A Digital Camera takes still photos but records the pictures on computer system disks or memory chips.
  • The information contained can be uploaded to a computer system for viewing.
  • A Video Camera or Recorder (VCR) can record data that can be uploaded to the computer system with the right hardware.
  • Though it is not digital data, you can still get good results with the right software.
  • Both of these take huge amounts of storage.
  • Photos make for very large files.
  • A Web Cam is a tiny video camera designed especially to sit on your computer system.
  • It feeds pictures directly to the computer system as there would be no tape or film to develop.
  • Of course the length of the cable that connects the camera to the computer system would be a limiting factor.
  • But like any camera, it will take a picture of what you point it at.

Multimedia Business

  • Even basic office applications like a word processing package or a spreadsheet tool becomes a powerful tool with the aid of multimedia business.
  • Pictures, animation and sound can be added to these applications, emphasizing important points in the documents.

Virtual Reality

  • Virtual reality is a truly absorbing multimedia application.
  • It is an artificial environment created with computer system hardware and software.
  • It is presented to the user in such a way that it appears and feels real.
  • In virtual reality, the computer system controls three of the five senses.
  • Virtual reality systems require extremely expensive hardware and software and are confined mostly to research laboratories.


  • Another multimedia application is Videoconferencing.
  • Videoconferencing is conducting a conference between two or more participants at different sites by using computer system networks to transmit audio and video data.

Connecting Keyboard, Mouse, Monitor and Printer to CPU and Checking Power Supply

  • Connecting keyboard:
    • Keyboard has two models of connectors.
    • They are PS/2 keyboard and USB keyboard.
    • One can connect the keyboard to any one of the two ports depends on the model.
  • Connecting Mouse
    • Mouse has three models of connectors.
    • They are PS/2, serial mouse, USB mouse.
    • One can connect the mouse to any one of the three ports depending on its model.
  • Connecting monitor:
    • Monitors are connected to the video port of the CPU.
    • This port is also called VGA port.
    • The VDU’s connector wire is connected to the VGA port. (blue in color)
  • Connecting Printers:
    • Printer has two models of connectors.
    • They are parallel port printer and USB printer.
    • One can connect the printer to any one of the two ports depending on its model.

Checking Power Supply

  • The computer system gets its power from the external power supply to system through SMPS (Switch Mode Power Supply), which is the power supply unit of the computer system.
  • The external power chord is to be connected to the power supply plug in the computer system.
  • Switch on the mains.
  • Switch on the ‘Power On’ switch of the computer system usually located in the bottom side of the front panel.
  • The computer system should be switched on and the power supply fan must be running.
  • Thus, one can be assured that the computer system is getting proper power supply.

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