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Presented by :Er. ReshmaAssistant ProfessorApplied Science(CSE)Chandigarh UniversityGharuan (Mohali).

Basics of Computer

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Contents

• Definition• Classification of computers• Computers generations• Applications of computers• Block Diagram and its working• Peripheral Devices• Primary Storage Devices• Auxiliary Storage Devices• Computer Hardware and Software

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Definition: Computer

• Computer is an electronic device that can perform a variety of operations in accordance with a set of instructions called program.

• The term ‘computer is derived from the term ‘computare’, this means to calculate.

• It takes raw data as input from the user and processes these data under the control of set of instructions (called program) and gives the result (output) and saves output for the future use.

• It can process both numerical and non-numerical (arithmetic and logical) calculations.

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Classification of computers

• Computers differ based on their data processing abilities. • They are classified according to

– purpose, – functionality and – size.

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On the basis of purpose

Computers are classified as follows:• General purpose computers

– designed to perform a range of tasks. They have the ability to store numerous programs, but lack in speed and efficiency.

• Specific purpose computers – designed to handle a specific problem or to perform a specific task. A

set of instructions is built into the machine.

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On the basis of functionality

According to functionality, computers are classified as :• Analog Computer:

– It uses continuous physical phenomena such as electrical, mechanical, or hydraulic quantities to model the problem being solved.

• Digital Computer: – A computer that performs calculations and logical operations with

quantities represented as digits, usually in the binary number system.• Hybrid Computer (Analog + Digital):

– A combination of computers those are capable of inputting and outputting in both digital and analog signals.

– A hybrid computer system setup offers a cost effective method of performing complex simulations.

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On the basis of size

On the basis of size, computers are classified as follows:1. Super Computer• The fastest and most powerful type of computer.• very expensive and are employed for specialized applications that require

immense amounts of mathematical calculations. • For example, weather forecasting requires a supercomputer. • Other uses of supercomputers include animated graphics, nuclear energy

research, and petroleum exploration.

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2. Mainframe Computer• A very large and expensive computer capable of supporting hundreds, or

even thousands, of users simultaneously. • Mainframes are more powerful than supercomputers because they support

more simultaneous programs. • But supercomputers can execute a single program faster than a mainframe.• Difference between a supercomputer and a mainframe is that a

supercomputer channels all its power into executing a few programs as fast as possible, whereas a mainframe uses its power to execute many programs concurrently.

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3. Mini Computer • A midsized computer. • In size and power, minicomputers lie between workstations and

mainframes. • A minicomputer is a multiprocessing system capable of supporting from 4

to about 200 users simultaneously.

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4. Micro Computer or Personal Computer• Desktop Computer: a personal or micro-mini computer sufficient to fit on

a desk. • Laptop Computer: a portable computer complete with an integrated

screen and keyboard. It is generally smaller in size than a desktop computer and larger than a notebook computer. 

• Palmtop Computer/Digital Diary /Notebook /PDAs: a hand-sized computer. Palmtops have no keyboard but the screen serves both as an input and output device.

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5. Workstation• A terminal or desktop computer in a network. In this context, workstation

is just a generic term for a user's machine (client machine) in contrast to a "server" or "mainframe.“

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Features: 1. Transistor replaced the bulky Vacuum tubes in the first generation

computer. 2. Processing speed is faster than First Generation Computers (Micro

Second).3. Manufacturing cost was also very low.4. The size of the computer got reduced considerably.5. The input and output devices were faster.

Example: IBM 1400 and 7000 Series, Control Data 3600 etc.

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Block diagram and

working of computer system

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Block Diagram of computer

Input Unit

Storage Unit

Output Unit

Control Unit

ALU

Program and Data

Results

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Primary Components Of A Computer

• Input devices.• Central Processing Unit

(containing the control unit and the arithmetic/logic unit).

• Memory.• Output devices.• Storage devices.

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Input Unit

– This is the process of entering data and programs in to the computer system.

– It takes as inputs raw data and performs some processing, giving out processed data.

– Therefore, the input unit takes data from us to the computer in an organized manner for processing.

• Examples: Keyboard, mouse, joystick, scanner, touch screen etc.

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Storage Unit• The process of saving data and instructions permanently is known as storage. • For faster access and processing, data is first stored in the storage unit. • Storage devices are divided into two classes:

– Primary Devices : e.g. RAM,ROM– Secondary Devices: e.g. HDD, Floppy Disk, CD-ROM, CD-R, DVD etc.

The storage unit performs the following major functions: • All data and instructions are stored here before and after processing. • Intermediate results of processing are also stored here.

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Processing Unit• The task of performing operations like arithmetic and logical operations is

called processing. • Working: The Central Processing Unit (CPU) takes data and instructions from

the storage unit and makes all sorts of calculations based on the instructions given and the type of data provided. It is then sent back to the storage unit.

• It is further divided into two units:– Control Unit (CU)– Arithmetic Logical Unit (ALU) 

• The ALU and the CU of a computer system are jointly known as the central processing unit.

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Control Unit• The next component of computer is the Control Unit, which acts like the

supervisor seeing that things are done in proper fashion. • Control Unit is responsible  for  coordinating various operations using time

signal. It determines the sequence in which computer programs and instructions are executed.

• Things like processing of programs stored in the main memory, interpretation of the instructions and issuing of signals for other units of the computer to execute them.

• It coordinates the activities of computer’s peripheral equipment as they perform the input and output.

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Arithmetic Logical Unit (ALU) 

• After you enter data through the input device it is stored in the primary storage unit.

• The actual processing of the data and instruction are performed by Arithmetic Logical Unit.

• The major operations performed by the ALU are addition, subtraction, multiplication, division, logic and comparison.

• Data is transferred to ALU from storage unit when required. • After processing the output is returned back to storage unit for further

processing or getting stored.

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Output Unit

• This is the process of producing results from the data for getting useful information.

• Output is also stored inside the computer for further processing.• Examples: Printers, Monitors, LCD etc.

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Peripheral Devices• A peripheral is a device connected to a host computer, but not part of it. • It expands the host's capabilities, but does not form part of the core

computer architecture. It is often, but not always, partially or completely dependent on the host.

• A peripheral is generally defined as any auxiliary device such as a computer mouse, keyboard, hard drive, etc. that connects to and works with the computer in some way.

• There are three different types of peripherals: – Input,– Output, and – Storage

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Input/Output Devices

• Input/output devices are required for users to communicate with the computer.

• Input devices bring information INTO the computer • Output devices bring information OUT of a computer system. • These input/output devices are also known as peripheral devices.

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INPUT DEVICES

OUTPUT DEVICES

CPU AND MEMORY

Input Data from external world

Input data coded in internal form

Processed data in internal form

Results of Processing in human acceptable form

Role of Input/output Devices

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Input Devices

• Keyboard Devices• Point and Draw Devices• Data Scanning Devices• Digitizer• Electronic Card based Devices• Voice Recognition Devices• Vision Based Devices

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Keyboard

• The most common method of data input device is the keyboard.• It is a text base input device that allows the user to input alphabets,

numbers and other characters.

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• Alphanumeric Keypad – It consists of keys for English alphabets, 0 to 9 numbers, and special

characters like + − / * ( ) etc. • Function Keys

– There are twelve function keys labeled F1, F2, F3… F12.– The functions assigned to these keys differ from one software package

to another. • Special-function Keys

– These keys have special functions assigned to them and can be used only for those specific purposes. Functions of some of the important keys are defined below.

• Enter – It is similar to the ‘return’ key of the typewriter and is used to execute a

command or program.

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Point & Draw Devices• Used to rapidly point to and select a graphic icon or menu item from

multiple options displayed on GUI of screen.• Used to create graphic elements on screen like lines, curves, freehand

shapes.

• Examples:– Mouse, Trackball, joystick, light pen, touch screen.

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Mouse• The mouse is a small device used to point to a particular place on the

screen and select in order to perform one or more actions. • It can be used to select menu commands, size windows, start programs

etc.

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Mouse Actions• Left Click : Used to select an item. • Double Click : Used to start a program or open a file. • Right Click : Usually used to display a set of commands. • Drag and Drop : It allows you to select and move an item from one

location to another. • To achieve this ,place the cursor over an item on the screen, click the left

mouse button and while holding the button down move the cursor to where you want to place the item, and then release it.

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Trackball• It acts as a type of overturned mouse.• The ball is on the top side of object.• By rolling the ball you can move pointer on screen.• Some keyboards have inbuilt trackball.• The advantage of a track ball over a mouse is that it does not require as

much space as a mouse

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Joytstick• The joystick is a vertical stick which moves the graphic cursor in a

direction the stick is moved. • It typically has a button on top that is used to select the option pointed by

the cursor. • Joystick is used as an input device primarily used with video games

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Electronic Pen• It is a pen shaped device used to select objects on a display screen. • It is quite like the mouse (in its functionality) but uses a light pen to move

the pointer and select any object on the screen by pointing to the object. • Users of Computer Aided Design (CAD) applications commonly use the

light pens to directly draw on screen.

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Touch Screen• It allows the user to operate/make selections by simply touching the

display screen. • Common examples of touch screen bank ATMs.

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Touchpad• It is device that senses pressure to guide the pointer on the computer

screen.• It has two buttons used for clicking in same way as mouse.• It is popular pointing device in laptops.

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Scanning Devices• Data scanning devices are input devices, which are used for direct data

entry into the computer system from source documents.• Characteristics:

– Reduction in time– Demand high quality of input documents.

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Scanner• Scanner is an input device used for direct data entry from the source

document into the computer system. • It converts the document image into digital form so that it can be fed into

the computer. • Capturing information like this reduces the possibility of errors typically

experienced during large data entry.

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Bar Code Reader• A bar code is a set of lines of different thicknesses that represent a number. • Bar Code Readers are used to input data from bar codes. Most products in

shops have bar codes on them. • Bar code readers work by shining a beam of light on the lines that make up

the bar code and detecting the amount of light that is reflected back.

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Optical Character Recognition Device

• It is a scanner equipped with character recognition software (OCR Software) that converts images of the characters to equivalent ASCII codes.

• One widely known application is in banking, where OCR is used to process checks without human involvement. A check can be inserted into a machine, the writing on it is scanned instantly, and the correct amount of money is transferred.

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Optical Mark Reader• It is a scanner capable of recognizing pre-specified set of marks made by

pencil or pen.• Very useful for grading tests for objective type questions, or any input data

that is of choice or selection nature.• Technique used for recognition of marks involves focusing a light on a

page being scanned and detecting the reflected light patterns from marks.

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Digitizer• Input device for converting pictures, maps and drawings into digital form

for storage in computer.• This enables the operator to draw sketches directly.• Commonly used in area of computer aided design(CAD) by architects

and engineers for design cars, building, medical devices, robots, mechanical parts etc.

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Voice Recognition Devices

• Input device that allow a person to enter a data into computer system by speaking.

• The “Microphones - Speech Recognition” is a speech Input device. To operate it we require using a microphone to talk to the computer. Also we need to add a sound card to the computer.

• The Sound card digitizes audio input into 0/1s .

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Vision Input Systems

• Allows the computer to accept input just by seeing the object.• Digital Camera• A digital camera can store many more pictures than an ordinary camera.• Pictures taken using a digital camera are stored inside its memory and can

be transferred to a computer• A digital camera takes pictures by converting the light passing through the

lens at the front into a digital image.

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Output Devices

• These usually receive data from the CPU and change it into a form which can be understood by humans.

• Monitors• Printers• Plotters• Screen Image Projectors• Voice Response Systems

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Types of Output• Soft Copy Output

– Not produced on paper or some material that can be touched.– Temporary in nature and vanish after use.– Examples.

• Output displayed on terminal screen, spoken out by voice response systems.

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Hard Copy Output• Produced on a paper or some material that can be touched.• Permanent in nature can be kept in paper files and used later without using

computer.

• Examples are output produced by printers and plotters.

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Monitors

• Monitor is an output device that resembles the television screen and uses a Cathode Ray Tube (CRT) to display information.

• The monitor is associated with a keyboard for manual input of characters and displays the information as it is keyed in.

• It also displays the program or application output. • Like the television, monitors are also available in different sizes.• A beam of electrons is fired from an electronic gun at back of the tube.• This strikes with the front of tube that is covered with phosphors cent

material which glow when struck by electrons.

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LCD• It stands for Liquid Crystal Display.• It make use of tiny transistors to emit light and create an image.• They are thinner and lighter and draw much less power than cathode ray

tubes (CRTs).

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LED• LED (Light Emitting Diode) TVs are simply LCD TVs with a different

kind of backlighting. The screen remains the same but LEDs are used in place of Cold Cathode Fluorescent Lamps (CCFL) that are found in most LCD TVs. 

• The use of LED lighting allows the TV to be thinner than standard LCD TVs.

• LED TVs can consume up to 40% less power than a LCD TV of similar size. 

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Printers

• Printers produce hard copy of the output on paper.• Based on the technology used, they can be classified as Impact or Non-

impact printers.• Impact printers use the typewriting printing mechanism wherein a hammer

strikes the paper through a ribbon in order to produce output. Eg. Dot Matrix, character printers.

• Impact printers can be used to generate multiple copies by using carbon paper or its equivalent.

• Non-impact printers do not touch the paper while printing. They use chemical, heat or electrical signals to carve the symbols on paper. Eg. Inkjet, Laser etc.

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Dot Matrix Printers• These are character printers that form characters and all kind of images as

pattern of dots.• Can print many special characters, different sizes of print and graphics

such as graphs and charts.• Slow, with speeds ranging from 30 to 600 characters per second.• Cheap in both initial cost and cost of operation.

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Inkjet Printers• Character printers that form characters by and all kinds of images by

spraying small drops of ink on paper.• Can print many special characters, different sizes of print and graphics

such as graphs and charts.• These are non-impact printers . Hence, they cannot produce multiple

copies of document in single print.• Slower than dot matrix printers with speeds between 40 to 300 characters

per second. • Offer higher quality than dot matrix printers.• More expensive.• They preferred by individuals and organizations if the speed of printing is

not an important factor.

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Drum Printers• Line printers that print one line at a time.• Have a solid cylindrical drum with characters embossed on its surface in

the form of circular bands.• Set of hammers mounted in front of the drum in such a manner that an

inked ribbon and paper can be placed between hammers and the drum.• Can print a pre-defined set of characters in a pre-defined style as that is

embossed on the drum.• Cannot print any shape of characters, different sizes of print, and graphics

such as charts and graphs.• Impact printers and usually monochrome.• Drum of these printers is expensive and cannot be changed often.• Typical speeds are 300 to 2000 line per minute.

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Chain/Band Printers• Can only print pre-defined set of characters that are embossed on the chain

used in the printer.• Cannot print any shape of characters, different sizes of print, and graphics

such as charts and graphs.• Are Impact printers can be used to generate multiple copies by using

carbon paper or its equivalent.• Are usually monochrome.• Speed are from 400 to 3000 lines per minute.• Chain/band of these printers can be easily changed.

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Laser Printers• Page printers that print one page at a time.• Produce very high quality output having resolution in the range 600 to

1200 dpi(dots per inch).• Can print any shape of characters, different sizes of print, and graphics

such as charts and graphs.• Non-impact printers.• Very high speed laser printers can print 500 to 1000 pages per minute.• More expensive than other printers.

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Plotters• Plotters are an ideal output device for architects, engineers, who need to

routinely generate high precision hard copy graphics out of widely varying sizes.

• Eg. Used in design of mechanical components of aircraft or car, architectural plan of buildings, engineering design applications etc.

• Two commonly used types:– Drum Plotters– Flatbed Plotters

• Drum: Paper on which the design has to be made is placed on drum that can rotate in both clockwise and anticlockwise directions.

• Flatbed: Paper on which design has to be made is spread and fixed over a rectangular flatbed table.

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Screen Image Projectors• An output device that can be directly plugged to a computer system for

projecting a information from computer onto a large screen.• Useful for making presentations for group of people with direct use of

computer.• Full-fledged multimedia presentation with can be prepared and presented

using this facility.

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Voice Response Systems• Voice response systems has an audio response device, which produces

audio output.• Output is temporary.

• Types– Voice Reproduction Systems– Speech Synthesizer

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Voice Reproduction Systems• Produces audio output by selecting from a set of pre-recorded audio

responses.

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Speech Synthesizer• It converts text input into spoken words.• Used for applications such as:• For reading out text information to blind persons.• Allowing those persons who cannot speak to communicate effectively.• Translating entered text into spoken words in a selected language.

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Memory and Storage Devices

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Storage• Information and documents are stored in computer storage so that it can be

retrieved whenever they are needed later on. • Computer storage is the storing of data in an electromagnetic or optical

form to be accessed by a computer processor. • It is a hardware designed to store information.• It is of two types: • Primary storage device : It is main storage unit to hold information ready

for processor to use while processing. It is small and quick. Exp:- RAM and Cache Memory.

• Secondary storage device : It is a device that hold information until it is deleted of overwritten. It also called “additional or auxiliary memory”. It is used to store large volume of data on permanent basis. Exp:- Hard disk drive, floppy disk drive etc.

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Methods of accessing data

• Sequential or Serial Access: information can only be retrieved in the same sequence in which it is stored. So access time depends upon data location. Eg. Magnetic Tape.

• Direct or Random Access : information can be retrieved randomly from any where within the storage locations. It is need not to go sequentially. Hence for retrieval of information required approximately equal time for each location. Eg. Magnetic Disk, Optical Disk.

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Units for data Measurement

• Bit:Short for binary digit, the smallest unit of information on a machine. • A single bit can hold only one of two values: 0 or 1. More meaningful

information is obtained by combining consecutive bits into larger units. • Byte: a byte is composed of 8 consecutive bits.• Kilobyte (KB)• Megabyte (MB)• Gigabyte (GB)• 8 Bits = 1 Byte • 1024 Byte = 1 KB • 1,048,576 Bytes = 1024 KB = 1 MB • 1,073,741,824 Bytes = 1024 MB = 1 GB

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Primary Memory

• Volatile RAM(Random Access Memory)

DRAMSRAM

• Nonvolatile ROM(Read Only Memory) PROM EPROM EEPROM

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Primary Memory• Also known as main storage or memory.• It is the main area in a computer in which data is stored for quick access by

the computer's processor. • Nowadays, the term random access memory (RAM) - or just memory - is

used instead of primary, main storage or core memory.• It is directly accessible to the CPU.• The capacity of RAM in terms of data storage is less, but it offers a very

fast access rate.• Therefore, it is relatively more expensive.• It is highly volatile in nature.• The problem of volatility can be avoided using Read Only Memory

(ROM). Though ROM retains the program instructions it does not allow to add or change them.

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• The Read and write (R/W) memory of a computer is called RAM. User can write information to it and read information from it.

• With RAM any location can be reached in a fixed ( and short) amount of time after specifying its address.

• RAM holds data and processing instructions temporarily until the CPU needs it.

• There are two basic types of RAM :(i) Dynamic RAM (ii) Static RAM

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Dynamic RAM

• DRAM refreshed there data every instance of time and retain the data for a very short span of time.

• It loses its stored information in a very short time (for milli sec.) even when power supply is on.

• They store information in memory cell made up of transistors and capacitors.• Three to four transistors are required for a Dynamic RAM,• D-RAM’s are cheaper.• This refresh operation happens automatically thousands of times per second.• The downside of all of this refreshing is that it takes time and slows down the

memory.• Dynamic RAM is used to create larger RAM space system

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Static RAM

• S-RAM retains stored information only as long as the power supply is on. • Costlier. • Higher speed than D-RAMs. • Store information in Flip-Flop.• Six to eight transistors are necessary for a Static RAM.• No refreshing option is available in Static RAM.•  Static RAM create speed- sensitive cache.• Consumes more power than Dynamic RAM.• For accessing a data or information, Static RAM takes less time than

Dynamic RAM.• Dynamic RAM has higher storage capacity than Static RAM.

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Some other RAMS are :

(a) SDRAM (Synchronous DRAMS), SGRAMs (Synchronous Graphic RAMs) – RAM chips use the same clock rate as CPU uses. – They transfer data when the CPU expects them to be ready.

 (b) DDR-SDRAM (Double Data Rate – SDRAM)

– This RAM transfers data on both edges of the clock T i.e. 2 operations per clock cycle

– therefore the transfer rate of the data becomes doubles.

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ROM

• Read only memory• Its non volatile memory.• It’s used for the permanent storage of information.• Information can not be written into a ROM by the users/programmers. • The contents of ROMs are decided by the manufactures.

Types of ROM:

1. Programmable ROM• Its contents are decided by the user. • The user can store permanent programs, data etc in a PROM. • The data is fed into it using a PROM programs.

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2. Erasable PROM• The stored data in EPROM’s can be erased by exposing it to

UV light for about 20 min. • It’s not easy to erase it because the EPROM IC has to be removed

from the computer and exposed to UV light.• The entire data is erased and not selected portions by the user.

EPROM’s are cheap and reliable.

3. Electrically Erasable PROM• The chip can be erased & reprogrammed on the board easily byte by

byte. • It can be erased with in a few milliseconds. • There is a limit on the number of times the EEPROM’s can be

reprogrammed, i.e.; usually around 10,000 times.

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4. Flash Memory • It is a variation of electrically erasable programmable read-only memory

(EEPROM)• EEPROM unlike flash memory, is erased and rewritten at the byte level,

which is slower than flash memory updating. • • It uses one transistor memory .• Low power consumption• Lower cost & • Higher reliability. • Its used in all power, digital cameras, MP3 players, Memory Card etc.

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Cache Memory

• Cache memory– High speed memory that a processor can access more rapidly than

main memory.• It is commonly used for minimizing processor memory speed mismatch.• It is extremely small fast memory between CPU and main memory whose

access time is closer to the processing speed of CPU.• It is temporarily used to store very active data and instructions during

processing.• It can be either a reserved section of main memory or an independent high-

speed storage device.

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• Cache memory is sometimes described in levels of closeness and accessibility to the microprocessor.

• An L1  cache is on the same chip as the microprocessor. •  L2  is usually a separate static RAM (SRAM) chip. The main RAM is

usually a dynamic RAM (DRAM) chip.• When data are found in the cache, it is called a cache hit, and the

effectiveness of a cache is judged by its hit rate• Many cache systems use a technique known as smart caching, in which the

system can recognize certain types of frequently used data. • The strategies for determining which information should be kept in the

cache constitute some of the more interesting problems in computer science.

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Registers

• Registers are special memory units that are used to hold information on a temporary basis as the instructions are executed by CPU.

• Registers are a part of CPU (not main memory) of computer.• The length of the register sometimes called the word size equals the

number of bits it can store.• With all other parameters same CPU with 32-bit register can process data

twice larger than 16-bit register.

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Auxiliary Memory

• Also known as external memory or secondary memory.• It holds information until it is deleted or overwritten regardless if the

computer has power. • Primary storage is accessed much faster than secondary storage because of

the price and size limitations.• Example: Floppy disk drive , Hard disk drive, CD-ROM, DVD etc.

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Examples of Auxiliary Devices

Floppy Disk

• It’s a circular disk coated with magnetic oxide and enclosed within square plastic cover (Jacket).

• It’s available in different size, but the most commonly used floppy is 3½.• Data up to 1.44 MB can be stored in it. • Floppies are available in 2 sizes, 3.5 inch & 5.25 inch. The 3.5 inch size

floppy is mostly used

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Hard Disk • Hard disks are made of aluminum or other metal alloys which are coated

on both sides with magnetic material. • Unlike floppy disks, hark disks are not removable from the computer. • For increasing storing capacity several disks are packed together &

mounted on a common drive to form a disk pack. • A disk is also called a platter.

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Disk Access Time

• Disk access time is the interval between the instant a computer makes a request for transfer of data from disk system to primary storage and the instant this operation is completed.

• Disk access time depend upon following three parameters– Seek Time: It is the time required to position the read/write head over

the desired track.– Latency: Time required to spin the desired sector under the read/write

head– Transfer Rate: Rate at which data is read/written to the disk

Magnetic Tape

• Magnetic Tape can be used to perform both functions -input and output. • Magnetic tapes are used for large computers like mainframe computers

where large volume of data is stored for a longer time. • The cost of storing data in tapes is inexpensive.

Advantages • Compact• Economical• Fast• Long term Storage and Re-usability

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Magnetic disk

• Circular like a disk and coated with magnetic material. • It rotates with very high speed inside the computer drive. • Data is stored on both the surface of the disk. • Magnetic disks are most popular for direct access storage device. • Each disk consists of a number of invisible concentric circles called tracks. • The information stored in a disk can be read many times without affecting

the stored data. • But to write a new data, then the existing data is erased from the disk and

new data is recorded.

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Optical Disk

• Information is written to or read from an optical disk or tape using laser beam.

• Optical disks are not suitable memory storage units because their access time is more than that of hard disks.

• Their advantage is that they have very high storage capacity. • Types of optical memory are: CD –ROM, CD-R, CD-RW, DVD-ROM,

DVD-R and DVD-RW. • Information on a CD-ROM is written at the time of manufacture.• CD-R/W of 700 MB are available.• A DVD-ROM is similar to CD-ROM. It uses shorter wave length of laser

beam and hence, stores more data than CD-ROM.

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Compact Disk/ Read Only Memory (CD-ROM)

• CD-ROM disks are made of reflective metals. • CD-ROM is written during the process of manufacturing by high power

laser beam.• Here the storage density is very high, storage cost is very low and access

time is relatively fast. • Each disk is approximately 4 1/2 inches in diameter and can hold over

600 MB of data. • As the CD-ROM can be read only we cannot write or make changes into

the data contained in it. 

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Write Once Read Many (WORM)

• WORM allows the user to write data permanently on to the disk. • Once the data is written it can never be erased without physically

damaging the disk. • Data can be recorded from keyboard, video scanner, OCR equipment and

other devices. • The advantage of WORM is that it can store vast amount of data

amounting to gigabytes. • Any document in a WORM can be accessed very fast, say less than 30

seconds.

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Erasable Optical Disk

• These are optical disks where data can be written, erased and re-written. • This also applies a laser beam to write and re-write the data.

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Computer Components

• The two main components which when combined makes a computer system are: Hardware Software

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Computer Hardware

• Hardware means the physical structure of a computer. • Example: RAM, ROM, motherboard, modem, wireless chip, Keyboard,

Mouse, Monitor, Printers etc.

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Computer Software

• It is the collection of computer programs, procedures and documentation that performs different tasks on a computer system.

• Different types of software are:– Application Software: It enables the end users to accomplish certain

specific tasks. – Business software, databases and educational software are some forms

of application software. – Different word processors, which are dedicated to specialized tasks to

be performed by the user, are other examples of application software.

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• Programming Software: These software come in the form of tools that assist a programmer in writing computer programs.– Computer programs are sets of logical instructions that make a

computer system perform certain tasks. – Compliers, interpreters, linkers and text editors are some of the basic

tools used in programming software. – Compilers translate source code written in a programming language into

the language which a computer understands (mostly the binary form). – Compilers generate objects which are combined and converted into

executable programs through linkers. – Debuggers are used to check code for bugs and debug it.– Interpreters execute programs. They execute the source code or a

precompiled code or translate source code into an intermediate language before execution. 

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• System Software– It helps in running computer hardware and the computer system. – System software refers to the operating systems; device drivers,

systems and utilities.. • Malware

– Malware refers to any malicious software that is a threat to computer security.

– Computer viruses, worms, Trojan horses and shareware are malware.

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•  Utility Software– Also known as service routine, utility software helps in the

management of computer hardware and application software. – It performs a small range of tasks. Disk defragmenters, virus scanners

are some of the typical examples of utility software. • Data Backup and Recovery Software

– An ideal data backup and recovery software provides functionalities beyond simple copying of data files.

– This software often supports user needs of specifying what is to be backed up and when.

– Backup and recovery software preserve the original organization of files and allow an easy retrieval of the backed up data.

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Thanks…..

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