Monday, 11 January 2016



Explain the block diagram of computer and explain all parts in detail?

The computer system consists of three units:

1.  Input Unit
2. Central Processing Unit (CPU)
 3. Output Unit

Block diagram of a Computer:


                   Memory unit

                        Control Unit


Working Process of above diagram:
·        The program or data is entered through input unit like keyboard and that data is controlled by C .U.
·        The control unit sends this data  to the memory unit (M.U) for temporary storage i.e in RAM (Random Access Memory).
·        This temporary stored data is then sent to A.L.U (Arithmetic Logical Unit) for processing through C.U.
·        A.L.U processes this data and then this processed data sent it back to Memory Unit for permanent storage i.e. in hard disk,again through C.U.
·        This processed data can also be sent to output unit directly through control unit or it can also sent from permanently stored memory i.e M.U to the output unit.
·        Finally, this output unit will give the result

1.     Input: This is the process of entering data and programs in to the computer system. You should know that computer is an electronic machine like any other machine which 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.
2.     Central Processing Unit: It is the part of the computer that carries out the instructions of a computer program. It is the unit that reads and executes program instructions. Hence it is known as the Brain  of the computer. The CPU consists of storage or memory unit, Arithmetic Logic Unit (ALU) and control unit.
(a). Memory Unit: It is also known as the primary storage or main memory. It stores data, program instructions, internal results and final output temporarily before it is sent to an appropriate output device. It consists of thousands of cells called ―storage locations‖. These cells activate with ―off-on‖ or binary digits(0,1) mechanism. Thus a character either a letter or numerical digit is stored as a string of (0,1) Binary digits ( BITS). These bits are used to store instructions and data by their combinations.
(b) Arithmetic and Logical Unit(ALU): It is the unit where all Arithmetic operations (addition, subtraction etc.) and logical functions such as true or false, male or female are performed. Once data are fed into the main memory from input devices, they are held and transferred as needed to ALU where processing takes place. No process occurs in primary storage. Intermediate generated results in ALU are temporarily placed in memory until needed at later time. Data may move from primary memory to ALU and back again to storage many times before the process is finalized.

(c).Control Unit : The control unit controls all the activities of the computer.
3.         Output: This is the process of producing results from the data for getting usefulinformation. Similarly the output produced by the computer after processing must also be kept somewhere inside the computer before being given to you in human readable form. Again the output is also stored inside the computer for further processing.


Computer can be classified according to two different ways. They are                 
1.      According to the logic used by the computer.
2.      According to the size of the computer.
According to the logic used by the computer. It can be classified  into 3 types. They are
1.      Analgo Computers    2. Digital Computers 3. Hybrid Computers
Analgo Computers:  The computers which accept the data in the form of voltage (v) or current signals  and convert  them to numeric values  are called Analog Computers.
These Computers can measure physical quantities like temperature,speed etc..These Computers give only approximate results.
Ex: . A speedometer which measures the speed of vehicle , and  thermometer which measures the temperature of the body etc..
Digital Computers:   The computer  which accept the data in the form of binary digits (bits) representing ZERO (0)  and ONE  (1) are called as Digital Computers. Each one is called as a bit. Logically 0 indicates false and 1 indicates true.
            Digital Computers give more accurate and very faster results than analog computers.
            Digital Computers deal with counting rather than physical measurement. They accept the input data and instructions in the form of digits 0 to 9 , alphabets ( A to Z) or special symbols like + , * ,- ,/ ,$ ,% etc….   In this there are TWO purpose of digital computers. They are
1.      General Purpose Digital Computer 2.     Special Purpose Digital Computer
General Purpose Digital Computers are designed to perform of different jobs or applications. These computers can be used in solving a business problem as well as mathematical problem with same accuracy and consistency.
Special Purpose Digital Computers are designed to meet the need of special application.They are designed , made and used for only a single job. So they excute their tasks quickly and efficiently.
Hybrid Computers:   The computers which accept the data in the form of combination of voltage or signals or binary digits are known as Hybrid Computers. So , these computers are computers which have the features of both digital and analog computers.
These computers are very useful in scientific research and to perform specific job etc….
Ex:       In a hospital ICU ( Intensive Care Unit ) , Analog devices may measure a patient’s heart function, temperature and other vital signs. These measurements may then be converted into numbers and supplied to the digital device which may send as immediate signal to the nurses station if any abnormal reading are detected.
According to the SIZE , the computers are classified as follows:
1. Super computers  2. Mainframe computers     3.Mini computers     4. Micro computers
Super computers:     Super computers are large size computers and  these computers can be processed  billions of instructions per second. These systems are multiprocessor system  and it is used to do parallel processing. These systems are very expensive and powerful and used in the complex tasks. It is typically used for following applications.
·        Weather Information
·        Medicine
·        Real-time Animation etc…..
Mainframe computers:                   Mainframe computers are large size computers and these computers can be processed hundreds of millions of instructions per second. In this computers , RAM is much more than micro computers as well as mini computers and it supports 100 users in time sharing mode. These computers are used in large organizations like…
·        Railway reservations
·        Airlines reservations
·        Banking applications etc…..
Mini computers:       Mini computers are also large size computers and these computers and it supports multiuser environment. These computers are expensive  as compare to micro computers. The main memory RAM can be 1MB to 16 MB.These computers also used in large organizations like..
·        Reservation system
·        Banking and industries.
Micro computers  :   Micro computers are smallest category of digital computers in which a microprocessor performs the function of ALU and Control Unit. These computers are single user systems which means that a single user can operate only one system at a time.These computers are also classified  into types. They are
1.      Desktop computers  2. Laptop computers            3. Handheld computers
Desktop computers  ( Personal computers):             Desktop computers are also called as Personal computers or simply PC’s. Today the Desktop computers are most popular computer systems. They are usually easier to use and more affordable.
Laptop computers:                     Laptop computers are portable computers.They are light weight computers with a thin screen. They are also called as notebook computers because of their smll size.It can be easily carried from one place to another place.It has battery also.
Handheld computers:    Handheld computers are also called as a Personal Digital Assistants (PDA’s). These computers are pen based and battery – powered. These systems are small size and carried easily from one place to another place.


microprocessor is an electronic component that is used by a computer to do its work. It is a central processing unit on a single integrated circuit chip and it containing millions of very small components including transistorsresistors, and diodes that work together.
 Microprocessors help to do everything from writing to searching the Web. Everything a computer does is described by lots of precise instructions, and microprocessors carry out these instructions at incredible speed—many millions of times a second. 
Microprocessors were invented in the 1970s for use in embedded systems. The majority are still used that way, in such things as mobile phonescars, military weapons, and home appliances. Some microprocessors are microcontrollers, so small and inexpensive that they are used to control very simple products like flashlights and greeting cards that play music when you open them. A few especially powerful microprocessors are used in personal computers.


In computers, parallel processing is the processing of program instructions by dividing them among multiple processors with the objective of running a program in less time. In the earliest computers, only one program ran at a time.
A computation-intensive program that took one hour to run and a tape copying program that took one hour to run would take a total of two hours to run.
An early form of parallel processing allowed the interleaved execution of both programs together. The computer would start an I/O operation, and while it was waiting for the operation to complete, it would execute the processor-intensive program. The total execution time for the two jobs would be a little over one hour.


Embedded processor, a class of computer, or computer chip, embedded in various machines. These are small computers that use simple microprocessors to control electrical and mechanical functions.
They generally do not have to do elaborate computations or be extremely fast, nor do they have to have great input/output capability, and so they can be inexpensive. Embedded processors help to control aircraft and industrial automation, and they are common in automobiles and in both large and small household appliances.
One particular type, the digital signal processor (DSP), has become as prevalent as the microprocessor. DSPs are used in wireless telephones, digital telephone and cable modems, and some stereo equipment

What is Computer?

 Definition: A Computer is an electronic device for storing data , processing information and displays the desired (want) output in human readable form .
Especially computer is used to  type documents, send email, play games, and browse the Web. You can also use it to edit or create spreadsheets, presentations, and even videos.


A set of values used to represent different quantities is known as Number System". 
Some important number systems are as follows.
·         Decimal number system
·         Binary number system
·         Octal number system
·         Hexadecimal number system
Decimal number System
The Decimal Number System consists of ten digits from 0 to 9 (i.e 0 1 2 3 4 5 6 7 8 9 ). These digits can be used to represent any numeric value. The base of decimal number system is 10. It is the most widely used number system.


The value of digit 4     =          4x102    =          400
The value of digit 5     =          5x101  =          50       
The value of digit 3     =          3x100 =          3
The actual number can be found by adding the values obtained by the digits as follows:
400 + 50 + 3    =45310

Binary Number System

Digital computer represents all kinds of data and information in the binary system. Binary Number System consists of two digits 0 and 1. Its base is 2. Each digit or bit in binary number system can be 0 or 1. A combination of binary numbers may be used to represent different quantities like 1001.

Example: Convert 101112  to decimal number

101112             =          1 x 24 + 0 x 23 + 1 x 22 + 1 x 21 + 1 x 20
                        =          1 x 16 + 0 + 1 x 4 + 1 x 2 + 1 x 1
                        =          16 + 0 + 4 2 + 1
                        =          2310

Octal Number System

Octal Number System consists of eight digits from 0 to 7. The base of octal system is 8. Each digit position in this system represents a power of 8. Any digit in this system is always less than 8. Octal number system is used as a shorthand representation of long binary numbers.

Example: convert 458 to decimal number

458       =          4 x 81 + 5 x 80
            =          4 x 8 + 5 x 1
            =          32 + 5
            =          3710    

Hexadecimal number system

The Hexadecimal Number System consists of 16 digits from 0 to 9 and A to F. The alphabets A to F represent decimal numbers from 10 to 15. The base of this number system is 16. Each digit position in hexadecimal system represents a power of 16. The number 76416 is valid hexadecimal number. It is different from 76410 which is seven hundred and sixty four.

Example: Convert 3A16 to decimal number

3A16     =          3 x 161 + A x 16                                              
            =          3 x 16 + 10 x 1
            =          48 + 10
            =          5810

Primary Storage is also called as a Main Memory and it is the part of computer system. In this, the processor and CPU directly stores data and retrieve information. This memory is accessed by CPU in random manner.
The Primary Memory or Main Memory is implemented by two types of memory technologies. They are 1.RAM (Random Access Memory)  2.ROM (Read Only Memory)
1. RAM (Random Access Memory):          Ram is made of electronic chips that means made of semiconductor material just like processors. In RAM, transistors make up the individual storage cells which can each keep an amount of data. RAM is also called as RWM (Read and Write Memory).
RAM stores the data temporarily in the computer. RAM nature is VOLATILE that means data stored in computer, it is lost when we switch of the computer or if there is a power failure.
RAM can be both means it can be physically as well as in the amount of data it can hold. RAMs are two types. They are
1. SRAM (Static RAM)                       2. DRAM (Dynamic RAM)
1. SRAM (Static RAM):         The word Static indicates that the memory retains           (keep or maintain) its contents as long as electrical power is applied to the chip. However, data is lost when the power gets down due to the volatile. SRAM need not have to be refreshed on the regular basis
2. DRAM (Dynamic RAM):  DRAM unlike SRAM, it must be continually refreshed in order for maintain the data. DRAM is used for most system memory because it is cheap and small. DRAM used less chips than SRAM for the same amount of storage space.

2. ROM (Read Only Memory):       ROM is a permanent memory and it is provided by the manufacturer at the time of fabrication. They are two reasons why read-only
·        Permanent
·        Security
Permanent:   The values or data stored in ROM are always retained even when power is off .For this reason it is called as Non-Volatile and the hard disk is also Non-Volatile for this same reason but regular RAM is not.
Security:         Actually ROM refers only to mask ROM the oldest type of solid state ROM, which is fabricated with the desired data permanently stored it and it can never modified. But modern types semiconductor ROM chips such as EPROM and flash EERPOM can be erased and re-programmed multiple times.
            ROM has different types of Rom’s.  They are
·        MROM ( Masked ROM)
·        PROM  (  Programmable ROM)
·        EPROM(  Erasable PROM)
·        EEPROM( Electrically Erasable PROM)
MROM (Masked ROM):      It is a hard-wired device that contained pre-programmed set of data or instructions.
PROM (Programmable ROM):        PROM is read only memory that can be modified only once by user. The user buys a blank PROM and enters the desired contents using PROM programmer. It cannot be erasable.
EPROM (Erasable PROM):   EPROM can be erased and re-programmed and it can be erased by exposure to strong ultraviolet light (typically for 10 minutes or longer), then re-written with a process that again requires application of higher than usual voltage.
EEPROM (Electrically Erasable PROM):     EERPOM is programmed and erased electrically. It can be erased and re-programmed about 10 thousand times. Both erasing and programming take about 4 to 10 milliseconds. In this, any location can be selectively erased and programmed and it can be erased 1 byte at a time.


Secondary Storage Device is also called as External Storage devices. Secondary Storage Devices are used to store data and instructions permanently. The nature of secondary storage devices is Non-Volatile that means it remains its data and instructions even after power is shut off. There are 2 types’ secondary storage devices. They are
1. Sequential Access Storage Devices (ex… Tape Drives)
2. Direct Access Storage Devices (ex…. Disk Drives)
1. Sequential Access Storage Devices:   Sequential means step by step processing. The data stored on SASD is accessed sequentially by the computer that is to access 100th record; it has to traverse the previous 99 records. It’s like, music cassette to listen 4th song you will have to forward first three songs. Magnetic Tapes are sequential access storage devices.
Magnetic Tape:   It is sequentially accessed storage medium. Basically it is used for back up storage. The magnetic medium is a thin plastic reel (Mylar) coated with iron oxide substance that can be magnetized. Information is represented as magnetized or Non-magnetized and spots represented 1’s and 0’s .In this, read/write head cannot jump to desired point so that the tape must be read or written sequentially.
 Mainly tapes are used with mainframe and minicomputer is stored on detachable reels. In this, we can record the data in 3 places. They are
v Recoding data on magnetic tape
v Recording data on tape drive
v Recording data on tape controller
Recording data on magnetic tape:   Data is recorded on magnetic tape across width as rows of magnetic spots and spaces divided into Columns. These are called as tracks or channels which run onto the entire length of the tape.
Recording data on tape drive:   A magnetic tape drive is used for storage and retrieval of information stored on magnetic tape. The tape drive consists of read/write heads which stores data on tapes.
Recoding data on tape controller:   A tape drive is connected to and controlled by controller which interprets the commands for the working of the tape drive.
Advantages: High storage capacity, Low cost, Re–usability and portability.
Disadvantage is tape is sequential access device so it is not possible for data fast accessing
2. Direct Access Storage Devices:    It can access the data directly. The access of data in direct devices is irrespective of the location of data stored on media. The time taken to retrieve 1st and 100th record is almost same. In this data accessing is very faster than the sequential access devices. It has different types of devices.  They are
v Floppy Disk (Magnetic Disk)
v Hard Disk (Magnetic Disk)
v Compact Disk (Optical Disk)
Floppy Disk: It is made of magnetic only. And it is direct access storage. It was the primary storage data and transferring the data until the CD-ROM drive captured the market.
A floppy disk was invented in 1967 at IBM by Alan shugart. Initially the disks were 8 inch in size which later evolved into the 5.25 inch diskette. A floppy disk drive is an electromechanical device that reads and writes data on small circular coated (iron oxide) plastic. The data is written on tracks which are concentric rings of data.
Earlier, the capacity of the disk was only 360 KB. Almost all computers these days have 3.5 inch drives and having capacity of 1.44 MB covered a rigid envelope. Bigger floppies are obsolete now.
To read/write, update, store and retrieve data from the floppy disk, a special mechanism is required known as Floppy Disk Drive (FDD).
Major parts of FDD:
v Read/write heads
v Drive motor
v Stepper motor
v Mechanical frame
v Circuit board
Storage Capacity:  Floppy disk storage capacity depends on the following factors.
v Data is stored on one side or double side
v Data recording density that is number of bits stored per inch (bpi).
v Track density means tracks per inch on which data is recorded.
Hard Disk:   Hard disk drive is the main device and it is usually largest data storage device in a computer. A hard disk drive is made up of metal platters coated with a thin film of magnetic material. The nature of hard disk drive is Non-Volatile that means the data cannot delete when the power is shut off because data is permanently stored.
A hard disk is generally the fastest of the secondary storage devices, and it has the largest capacity, approximately the same as magnetic tapes. There are 2 types of hard disks .They are
v Internal hard disk
v External hard disk
Internal hard disk: These types of hard disks are used internally in computer system that means building with CPU when you purchasing the computer system.
External hard disk:  These types of hard disks are used for taking data from one computer system to another computer system and it is substitute for portable storage.
A hard disk is divided into tracks and sectors. Data on this hard disk is positioned into these tracks and sectors so they can be easily read by heads and also to help reduce fragmentation on the hard disk.
Data on a hard disk are access by 2 methods. They are
v Fixed head
v Moving head
Fixed head: Hard disk with fixed heads have a read/write head for each track on the hard disk, since there is no moving of head to access data so the data access time is faster for fixed head hard disk drive.
Moving head: A moving head hard disk is one in which one or more read-write head are attached to a movable arm which allows each head to cover many tracks of information.

Compact Disk:   It is optical disk and optical disk can store the data /write by lasers only.
The compact disk-CD was invented in 1982 by two well known companies (Philips and Sony). Initially it was an audio CD, digital audio. CD shape is round medium and it was made of molded polymer. It is a small optical disk on which data such as music, text, or graphic images is digitally encoded. CDs contain computer data in the same way as the hard disk.
A CD is a form of data storage that can transfer data up to the speed of 7800 KB/s. A standard 120 mm CD holds data up to 700 MB and 70 minutes of audio. It has different types of CDs. They are
v CD-DA      (Audio CD, Digital Audio by Philips and Sony )
v Photo CD (It is one format that holds digitized photographs and sound , developed by Kodak and Philips)
v VCD    (Video CD can hold around 70 minutes of video footage)
v CD-R   (CD-Rs are WORM Write Once Read Many) the user can write to each blank disk only once. After written once, it behaves like CD-ROM.
v CD-RW (Rewritable or erasable –CD, developed in 1995. These disks can be erased and rewritten at any time)
v DVD (Digital Versatile Disc is extends of CD. It can be used for storing data and disk capacity is 4.7 GB to 17 GB , it access rates of 600 KBps to 1.3 MBps)


Devices are used to provide data and instructions to the computer are called Input devices.  Some important input devices are
1. Keyboard 2.Mouse 3. Joy Stick 4.Light pen 5.Track Ball 6.Scanner 7.Microphone 8.Bar Code Reader
Keyboard is the most common and very popular input device which helps in inputting data to the computer. Keyboards are of two sizes 84 keys or 101/102 keys, but now keyboards with 104 keys or 108 keys are also available for Windows and Internet.
Typing Keys
These keys include the letter keys (A-Z) and digit keys (0-9) which generally give same layout as that of typewriters.
Numeric Keypad
It is used to enter numeric data or cursor movement. Generally, it consists of a set of 17 keys that are laid out in the same configuration used by most adding machines and calculators.
Function Keys
The twelve function keys are present on the keyboard which is arranged in a row at the top of the keyboard. Each function key has unique meaning
Control keys
These keys provide cursor and screen control. It includes four directional arrow keys. Control keys also include Home, End, Insert, Delete, Page Up, Page Down, Control(Ctrl), Alternate(Alt), Escape(Esc).
Special Purpose Keys
Keyboard also contains some special purpose keys such as Enter, Shift, Caps Lock, Num Lock, Space bar, Tab, and Print Screen.


Mouse is most popular pointing device. It is a very famous cursor-control device having a small palm size box with a round ball at its base which senses the movement of mouse and sends corresponding signals to CPU when the mouse buttons are pressed. Generally it has two buttons called left and right button and a wheel is present between the buttons.


Joystick is also a pointing device which is used to move cursor position on a monitor screen. It is a stick having a spherical ball at its both lower and upper ends. The lower spherical ball moves in a socket. The joystick can be moved in all four directions. The function of joystick is similar to that of a mouse. It is mainly used in Computer Aided Designing (CAD) and playing computer games.
Light Pen
Light pen is a pointing device which is similar to a pen. It is used to select a displayed menu item or draw pictures on the monitor screen. It consists of a photocell and an optical system placed in a small tube. When the tip of a light pen is moved over the monitor screen and pen button is pressed, its photocell sensing element detects the screen location and sends the corresponding signal to the CPU.
Track Ball
Track ball is an input device that is mostly used in notebook or laptop computer, instead of a mouse. This is a ball which is half inserted and by moving fingers on ball, pointer can be moved. Since the whole device is not moved, a track ball requires less space than a mouse. A track ball comes in various shapes like a ball, a button and a square.
Scanner is an input device which works more like a photocopy machine. It is used when some information is available on a paper and it is to be transferred to the hard disc of the computer for further manipulation. Scanner captures images from the source which are then converted into the digital form that can be stored on the disc. These images can be edited before they are printed.
Microphone is an input device to input sound that is then stored in digital form. The microphone is used for various applications like adding sound to a multimedia presentation or for mixing music.

Bar Code Readers
Bar Code Reader is a device used for reading bar coded data (data in form of light and dark lines). Bar coded data is generally used in labeling goods, numbering the books etc. It may be a hand held scanner or may be embedded in a stationary scanner. Bar Code Reader scans a bar code image, converts it into an alphanumeric value which is then fed to the computer to which bar code reader is connected.


Any device that is capable of representing information on a computer is called an Output device. Output devices receive information from the CPU and present it to the user in the desired form.
Following are few of the important output devices which are used in a computer.
  • Monitors
  •  Plotters
  • Printers
  • Speakers
·         Monitors, commonly called as Visual Display Unit (VDU), are the main output device of a computer. It forms images from tiny dots, called pixels that are arranged in a rectangular form. There are two kinds of viewing screen used for monitors.
  • Cathode-Ray Tube (CRT)
  • Flat- Panel Display

Cathode-Ray Tube (CRT) Monitor

The CRT display is made up of small picture elements called pixels. The smaller the pixels, the better the image clarity, or resolution. It takes more than one illuminated pixel to form whole character, such as the letter ‘e’ in the word help. Most screens are capable of displaying 80 characters of data horizontally and 25 lines vertically.

Flat-Panel Display Monitor

The flat-panel display refers to a class of video devices that have reduced volume, weight and power requirement in comparison to the CRT. You can hang them on walls or wear them on your wrists. Current uses of flat-panel displays include calculators, video games, monitors, laptop computer, graphics display.
Printers:   Printer is an output device, which is used to print information on paper.
There are two types of printers:
  • Impact Printers
  • Non-Impact Printers
Impact Printers
The impact printers print the characters by striking them on the ribbon which is then pressed on the paper.  These printers are of two types
1.       Character printers     2.  Line printers

Character Printers

Character printers are the printers which print one character at a time.  These are further divided into two types:
  • Dot Matrix Printer(DMP)
  • Daisy Wheel

Dot Matrix Printer

In the market one of the most popular printers is Dot Matrix Printer. These printers are popular because of their ease of printing and economical price. Each character printed is in form of pattern of dots and head consists of a Matrix of Pins of size (5*7, 7*9, 9*7 or 9*9) which come out to form a character that is why it is called Dot Matrix Printer.

Daisy Wheel:

Head is lying on a wheel and pins corresponding to characters are like petals of Daisy (flower name) that is why it is called Daisy Wheel Printer. These printers are generally used for word-processing in offices which require a few letters to be sent here and there with very nice quality.

Line Printers

Line printers are the printers which print one line at a time.
These are of further two types
  • Drum Printer
  • Chain Printer

Drum Printer

This printer is like a drum in shape so it is called drum printer. The surface of drum is divided into number of tracks. Total tracks are equal to size of paper i.e. for a paper width of 132 characters, drum will have 132 tracks. Drum printers are fast in speed and can print 300 to 2000 lines per minute.

Chain Printer

In this printer, chain of character sets are used so it is called Chain Printer. A standard character set may have 48, 64, or 96 characters.
Non-impact Printers
·         Non-impact printers print the characters without using ribbon. These printers print a complete page at a time so they are also called as Page Printers. It faster than impact printers.
These printers are of two types
  • Laser Printers
  • Inkjet Printers

Laser Printers

These are non-impact page printers. They use laser lights to produce the dots needed to form the characters to be printed on a page.
  • It can be very high speed
  • It can be very high quality output
·        But cannot be used to produce multiple copies of a document in a single printing.

Inkjet Printers

Inkjet printers are non-impact character printers based on a relatively new technology. They print characters by spraying small drops of ink onto paper. Inkjet printers produce high quality output with presentable features.

Plotters are a specialist type of printer which is able to draw high quality image pieces of paper
They are used by engineers, architects and map-makers to draw plans of buildings, diagram of machines.
A plotter differs from a printer in that it draws images using a pen that can be lowered ,raised and moved across the paper to form continuous lines. The electronically controlled pen is moved around the paper by computer.
In the plotters ,there are pen-less.

Speakers:       As many users are using computers as a multimedia device for listening to music and watching movies, speakers have become an integrated part of the computer.  Mainly speakers are used for producing sound outputs. They convert the digital signals coming from computer to analog sound waves. Several sizes and wattage of speakers are available. A personal computer generally contains  210-500 watt speakers which can produce the sound for a small room only. To cover big area, amplified speakers and woofers systems are used.

            Language is the communication among human beings; different countries have different languages. Similarly in order to communicate with the computer user also needs to have language that should be understood by the computer. Basically languages are divided into two categories. They are
1. Low Level Language                                  2.High Level Language
Low Level Language:
            Low Level Computer Languages are machine codes. Computer cannot understand instructions given in high level languages or in English. It can only understand and execute instructions given in the form of machine language. There are two types of Low level languages
1. Machine Language                        2. Assembly Language
Machine Language:
            It is the lowest and most elementary level of programming language and it was the first type of programming language to be developed. Machine language is basically the only language which computer can understand. In fact, a manufacturer designs a computer to obey just one language, its machine code, which is represented inside the computer by string of binary digits o and 1.
Advantages of Machine Language:
            1. It makes fast and efficient use of the computer.
            2. It requires no translator to translate the code.
Disadvantages of Machine Language:
1.      All operation codes have to be remembered.
2.      All memory address has to be remembered.
Advantages of Assembly Language:
1.      It is easy to understand and use as compared to machine language.
2.      It is modified easily.
Disadvantages of Assembly Language:
            1. Like machine language, it is also machine dependent.

High Level Language:
            High Level Languages are basically symbolic languages that use English words and Mathematical symbols rather than mnemonic codes. Each instruction in the high level language is translated into many machine language instructions. There are different types High level languages. They are
(a) Algebraic Formula Type  (b) Business Data Processing
(c) String and List Processing (d) Visual Programming Languages
(a) Algebraic Formula Type:
            These languages are used to computational procedures for solving mathematical and statistical problems.
Ex:       BASIC (Beginners All Purpose Symbolic instruction Code) ,FORTRAN (Formula Translation)
(b)  Business Data Processing:
            These languages are used for maintaining the data processing procedures and file handling problems.
Ex:       COBOL (Common Business Oriented)
(c) String and List Processing:
            These are used for string manipulation including search patterns, inserting and deleting characters.
Ex:       OOP (Object Oriented Programming) like C++ and JAVA
(d)  Visual Programming Languages:
            These are designed for building Windows – based applications
Ex:       Visual Basic, Visual Java and Visual C
Advantages of High Level Language:
            1. User- friendly        2.They requires less time to write

 Computers can understand instructions only when they are written in their own language – the machine language. Therefore, a program written in any other language should be translated into machine language. The software that ―translates‖ the instructions of different languages is known as translators.
There are two types of translators. They are compilers and Interpreters
A Compiler checks the entire user – written program (known as the source program) and if it is error free, produces a complete program in machine language (known as object program). The source program is retained for possible modifications and corrections and the object program is loaded into the computer for execution. If the source program contains errors, the compilers produce a list of errors at the end of the execution of the program. I.e. a compiler translates the whole program before execution.
An interpreter does a similar job but in a different style. The interpreter translates
 One statement at a time and if it is error – free, executes.                               
         Thus an interpreter translates or executes the first instruction before it goes to the second, while a compiler translates the whole program before execution.
The major difference between compiler and interpreter is
1.      Error correction is very much simpler in the case of interpreter as it translates the statements in stages. The compiler produces an error list of the entire program at the end.
2.      Interpreter takes more time for the execution of the program compared to compilers as it translates one statement at a time.

INFORMATION TECHNOLOGY:       Information technology (IT) is the use of any computers, storage, networking and other physical devices, infrastructure and processes to create, process, store, secure and exchange all forms of electronic data.
Typically, IT is used in the context of enterprise operations as opposed to personal or entertainment technologies. The commercial use of IT encompasses both computer technology and telephony.
HARDWARE:  In information technology, any physical device which we can see and we can touch that device is belongs to computer system then it is called as Hardware. Like keyboard, monitor, mouse, printer, mouse etc….
SOFTWARE:   Software is program or set of instructions which is used to perform a particular task on the computer hardware then it is called as Software.
INFORMATION PROCESSING CYCLE:         There are four events in the sequence of events. The sequences of events, which make up the information processing cycle, are:

1.      Input—entering data into the computer.
2.      Processing—performing operations on the data.
3.      Output—presenting the results.
4.      Storage—saving data, programs, or output for future use.

The collection of raw data from the outside world so it can be put into an information system. Putting the acquired data into the information system.
Typical input devices:
Keyboards, mice, flatbed scanners, bar code readers, joysticks, digital data tablets (for graphic drawing), electronic cash registers

CPU Processor - Central Processing Unit
A central processing unit (CPU), or sometimes simply processor, is the key component in a digital computer capable of executing a program. It interprets computer program instructions and processes data. A CPU that is manufactured as a single integrated circuit is usually known as a microprocessor. Beginning in the mid-1970s, microprocessors of ever-increasing complexity and power gradually supplanted other designs, and today the term "CPU" is usually applied to some type of microprocessor.
In information processing, output is the process of transmitting the processing information
Essentially, output is the presentation of any data exiting a computer system. This could be in the form of printed paper, audio, video. In the medical industry this might include CT scans or x-rays. 
Typical output devices:

·         Pixels: Images are created with dots of lights called picture elements, or pixels. More pixels = higher resolution. Resolution is the maximum number of pixels the monitor can display
·         Laser - laser beams bond toner to paper
·         Ink jet - fine stream of ink
·         Dot Matrix - pins & ribbon

Storage or mass storage refers to various techniques and devices for storing large amounts of data. The earliest storage devices were punched paper cards, which were used as early as 1804 to control silk-weaving looms.
Examples of some mass storage devices
·         Disk storage – hundreds of thousands of cycles latency, but very large
o    Hard disks : Very fast and with more capacity than floppy disks, but also more expensive.
o    Floppy Disks: (almost obsolete!)
·         Tertiary storage –
o    Optical storage: Unlike floppy and hard disks, which use electromagnetism to encode data, optical disk systems use a laser to read and write data. Optical disks have very large storage capacity, but they are not as fast as hard disks. Examples: CD, CD-R, CD-RW, DVD or DVD-R
o    Tapes: Relatively inexpensive and can have very large storage capacities, but they do not permit random access of data.
·         Flash Memory – faster than disk storage, with up to 4GB or more of data, transferring (usually) over universal serial bus (USB)

The Global Positioning System (GPS) is a satellite-based navigation system made up of a network of 24 satellites placed into orbit by the U.S. Department of Defense. GPS was originally intended (planned) for military applications, but in the 1980s, the government made the system available for civilian (police or javaanulu) use.
The GPS is owned and operated by the U.S. Department of Defense but is available for general use around the world. Briefly, here's how it works:
·         21 GPS satellites and three spare satellites are in orbit at 10,600 miles above the Earth. The satellites are spaced so that from any point on Earth, four satellites will be above the horizon.
·         Each satellite contains a computer, an atomic clock, and a radio. With an understanding of its own orbit and the clock, it continually broadcasts its changing position and time. (Once a day, each satellite checks its own sense of time and position with a ground station and makes any minor correction.)
·         On the ground, any GPS receiver contains a computer that "triangulates" its own position by getting bearings from three of the four satellites. The result is provided in the form of a geographic position - longitude and latitude - to, for most receivers, within 100 meters.
·         If the receiver is also equipped with a display screen that shows a map, the position can be shown on the map.
·         If a fourth satellite can be received, the receiver/computer can figure out the altitude as well as the geographic position.
·         If you are moving, your receiver may also be able to calculate your speed and direction of travel and give you estimated times of arrival to specified destinations.
DATA BASE:   database is a collection of information that is organized so that it can easily be accessed, managed, and updated. In one view, databases can be classified according to types of content: bibliographic, full-text, numeric, and images.
DATABASE ADMINISTRATOR:        database administrator (DBA) is an IT professional responsible for the installation, configuration, upgrading, administration, monitoring, maintenance, and security of databases in an organization.
DATABASE MANAGEMENT:            A database management system (DBMS) is system software for creating and managing databases. The DBMS provides users and programmers with a systematic way to create, retrieve, update and manage data.
A DBMS makes it possible for end users to create, read, update and delete data in a database. The DBMS essentially serves as an interface between the database and end users or application programs, ensuring that data is consistently organized and remains easily accessible.
RELATIONAL DATABASE MANAGEMENT: relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as invented by E. F. Codd, of IBM's San Jose Research Laboratory. Many popular databases currently in use are based on the relational database model.
A relational database management system (RDBMS) is a program that lets you create, update, and administer a relational database. Most commercial RDBMS's use the Structured Query Language (SQL) to access the database, although SQL was invented after the development of the relational model and is not necessary for its use.
The leading RDBMS products are Oracle, IBM's DB2 and Microsoft's SQL Server.

Internet was conceived by the Advanced Research Projects Agency (ARPA) of the U.S. government in 1969 and was first known as the ARPANet. The original aim was to create a network that would allow users of a research computer at one university to "talk to" research computers at other universities. A side benefit of ARPANet's design was that, because messages could be routed or rerouted in more than one direction, the network could continue to function even if parts of it were destroyed in the event of a military attack or other disaster.
The internet is a global connection of computers. These computers are connected via a huge network of telecommunication links. The internet allows you to access to a whole resource of data and information stored at different sites (called hosts) and locations around the world. The communication links which inter connect each host computer use a common method of transmission known as TCP/IP, which stands for Transmission Control Protocol / Internet Protocol.
Internet connection helps us to:
1.     Read information on a wide range of topics
2.     Send or receive E-mail
3.     Down load useful programs such as virus detectors, file compression, decompression utility
4.     Share your opinions and your knowledge on a variety of topics through various new groups.
5.     Chat with other people anywhere in the world
6.     View interesting video‘s listen to music or wander through a 3-D world.

Requirements for connecting to the Internet:
a)     Modem: A modem is a peripheral device that allows a computer to connect and communicate with other computers. Modem stands for Modulator Demodulator.
b)     Web Browser: A browser is a software program that is necessary in order to view web pages on the web. Ex: Internet Explorer, Netscape Navigator, Mozilla Firefox, Microsoft outlook express etc.
c)      Telephone line: A telephone line is required to transfer data from one computer to another. The computer is connected to a modem, which, in turn, connected to a telephone line.
d) Subscription with Internet service provider (ISP): ISP‘s are companies that provide access to the internet. We need subscription with any ISP to get an Internet connection. Some of the ISPs in India are VSNL, MTNL.
World Wide Web (WWW):
Web is invented by TIM BERNERS LEE. It refers to the collection of information accessible on the internet. The web is similar to a library. It consists of millions & millions of pages of text, pictures, sounds and animation on various topics. These pages, called as web pages and these web pages are stored on different computers that are connected to the internet. The web pages have links between them i.e. when we click a certain word or picture in a page, it will take us to another page. These words or pictures that help to move from one page to another are called hyperlinks. A collection of related web pages is known as a web site. A web site can be accessed by means of a unique name assigned to it.

The Home Page is the first Web page that is displayed after starting a Web browser like Netscape's Navigator or Microsoft's Internet Explorer. The browser is usually preset so that the home page is the first page of the browser manufacturer. However, you can set it to open to any Web site. For example, you can specify that "" or "" be your home page. You can also specify that there be no home page (a blank space will be displayed) in which case you choose the first page from your bookmark list or enter a Web address.

Web browser is a software application used to locate, retrieve and display content on the World Wide Web, including Web pages, images, video and other files. As client, the browser is the client run on a computer that contacts the Web server and requests information. The Web server sends the information back to the Web browser which displays the results on the computer or other Internet-enabled device that supports a browser. There are no of web browsers are available. They are
1.      Google Chrome                    2.Mozilla Fire Fox                  3.Internet Explorer    4.Apple Safari            5.Opera

A Web site is a related collection of World Wide Web (WWW) files that includes a beginning file called a home page. A company or an individual tells you how to get to their Web site by giving you the address of their home page. From the home page, you can get to all the other pages on their site. For example, the Web site for IBM has the home page address of (The home page address actually includes a specific file name like index.html but, as in IBM's case, when a standard default name is set up, users don't have to enter the file name.) IBM's home page address leads to thousands of pages. (But a Web site can also be just a few pages.)
An access provider is any organization that arranges for an individual or an organization to have access to the Internet. Access providers are generally divided into two classes:
1.      Internet access providers (ISPs)   2.  Online service providers (OSPs).
ISPs can be local businesses that pay for a high-speed connection to one of the companies (such as AT&T, Sprint, or MCI in the U.S.) that are part of the Internet. They can also be national or international companies that have their own networks (such as AT&T's WorldNet or IBM's Global Services).     
An IAP (Internet access provider) is a company that provides individuals and other ISP companies access to the Internet. An IAP is a type of Internet service provider (
ISP). (The other main service that an ISP provides is Web site building and virtual hosting.) An IAP has the equipment and the telecommunication line access required to have POP on the Internet for the geographic area served. The larger IAPs have their own high-speed leased lines so that they are less dependent on the telecommunication providers and can provide better service to their customers. Among the largest national and regional ISPs are AT&T WorldNet, IBM Global Network.

OSPs, sometimes just called "online services," also have their own networks but provide additional information services not available to non-subscribers. America Online is the most successful example of an OSP.
In general, the companies sometimes identified as OSPs (in this usage) offer an extensive online array of services of their own apart from the rest of the Internet and sometimes their own version of a Web browser. Connecting to the Internet through an OSP is an alternative to connecting through one of the national Internet service providers, such as AT&T or MCI, or a regional or local ISP.
                                                                   INTERNET APPLICATIONS
There are several types of internet applications available. Some of the internet applications are.
1.      E-mail
2.      Telephone Networking
3.      Fax
4.      Online Services
5.      Chat
6.      Video Conferencing
E-mail: E-mail or electronic mail is a service for sending or receiving messages electronically through a computer network. The electronic mail uses various technologies that support electronic transmission of text, data and graphics.
Some of the features of E-mail are
1.      It is much faster than the normal mail. Messages can be sent within a matter of seconds to any part in the world.

2.      it can be sent to many people at the same time

3.      E-mail is cheaper than a phone call and an ordinary mail

4.      it can access information and file libraries on request

5.      E-mail user can have a mail box which is accessed through a computer terminal

6.      an E-mail message consists of two parts

a)      a header specifying the address of the sender and the address of the receiver

b)     the text of the message

7.     The mailing system allows selecting messages for reading, displaying, saving, deleting, forwarding and replying.

8.     Mailing list can be created to send the same message to a group of people

E-Mail Address: An E-Mail address consists of three parts
1.     The person‘s Login name

2.     @ sign

3.     Domain name

A domain represents organization, network, and country name
Ex: in this gurijalasudhakar is the user name and his account is in the domain Both the names are separated by the @symbol.
Telephone Networking:  A telephone network is a telecommunications network used for telephone calls between two or more parties.
There are a number of different types of telephone network:
·          Landline Network where the telephones must be directly wired into a single telephone exchange. This is known as the public switched telephone network or PSTN.
·          Wireless Network where the telephones are mobile and can move around anywhere within the coverage area.
·          Private Network where a closed group of telephones are connected primarily to each other and use a gateway to reach the outside world. This is usually used inside companies and call centers and is called a private branch exchange (PBX).
Public telephone operators (PTOs) own and build networks of the first two types and provide services to the public under license from the national government.                      Virtual Network Operators (VNOs) lease capacity wholesale from the PTOs and sell on telephony service to the public directly.
Fax:                  A fax (short for facsimile and sometimes called telecopying) is the telephonic transmission of scanned-in printed material (text or images), usually to a telephone number associated with a printer or other output device. The original document is scanned with a fax machine, which treats the contents (text or images) as a single fixed graphic image, converting it into a bitmap. In this digital form, the information is transmitted as electrical signals through the telephone system. The receiving fax machine reconverts the coded image and prints a paper copy of the document.
Online Services:       In the world wide there are no.of online services are available. Some of the important online services are.

Chat:      Chat is a text-based communication that is live or in real-time. For example, when talking to someone in chat any typed text is received by other participants immediately. This is different from other text-based communications such as mail where it could be a couple of hours, days, or weeks to receive a response.
There are also several million users chatting through other networks such as IRC. A good example of a chat on IRC is the Computer Hope chat.

Chat etiquette (Rules)

Below is a short list of chat etiquette that should be followed when chatting with others online.

1.      Behave the same way you would when talking to someone in real-life.
2.      Try your best to spell all words correctly and use proper punctuation.
3.      Remember no one is perfect, spelling errors and other mistakes are common in chat.
4.      Do not WRITE IN ALL CAPS as it makes you appear as you're yelling.
5.      Do not send other chat users private messages without asking them first.
Video Conferencing:      A videoconference is a live connection between people in separate locations for the purpose of communication, usually involving audio and often text as well as video. At its simplest, videoconferencing provides transmission of static images and text between two locations. At its most sophisticated, it provides transmission of full-motion video images and high-quality audio between multiple locations.

Videoconferencing software is quickly becoming standard computer equipment. For example, Microsoft's NetMeeting is included in Windows 2000 and is also available for free download from the NetMeeting homepage. For personal use, free or inexpensive videoconference software and a camera afford the user easy - and cheap - live connections to distant friends and family. Although the audio and video quality of such a minimal setup is not high, the combined benefits of a video link and long-distance savings may be quite persuasive.

Uniform Resource Locator: (URL):
A URL (Uniform Resource Locator, previously Universal Resource Locator). A URL is a type of URI (Uniform Resource Identifier, formerly called Universal Resource Identifier.)
Each web site has a unique address commonly referred to as a URL. A URL specifies the exact location of the web page on the internet. A typical web address or URL looks as http://
Explanation of the example URL:
http: --à  Identifies protocol necessary to retrieve the file.
www: ----à Indicates that the site is on the world wide web
Microsoft:-à Indicates the name of the web site
.com: -à  Indicates the domain type of the web site

Anotomy of a URL:


URL anatomy explained

Protocol:  The protocol declares how your web browser should communicate with a web server when sending or fetching a web page or document. The most common protocol is http which stands for Hypertext Transfer Protocol. Another common protocol is https which stands for Hypertext Transfer Protocol Secure. You'll see this on secure pages, like shopping sites and log in pages.
Sub domain:   A sub domain is a sub-division of the main domain name.                                                 For example, and are sub domains of the domain name
Domain name:   A domain name is a unique reference that identifies a web site on the internet.         For example A domain name always includes the top-level domain (TLD), which in Doepud's case is uk. The co part is shorthand for commercial and combined is called a second-level domain (SLD).

Port:    The port number is rarely visible in URLs but always required. When declared in a URL it comes right after the TLD, separated by a colon. When it's not declared and in most cases where the protocol is http, port 80 is used. For https (secure) requests port 443 is used.
Path:    The path typically refers to a file or directory on the web server, e.g./directory/file.php.
Query:    A query is commonly found in the URL of dynamic pages and is represented by a question mark followed by one or more parameters. The query directly follows the domain name, path or port number.
Parameters:    Parameters are snippets of information found in the query string of a URL. With reference to the Google query above, the parameters follow the question mark and are separated by an ampersand (&) character so they can be understood individually and used to display content on that page.
Fragment:    A fragment is an internal page reference, sometimes called a named anchor. It usually appears at the end of a URL and begins with a hash (#) character followed by an identifier.

Search Engine:
Search engines are utilities used to search for information on the web. A user interface is provided where you can enter the word or phrase you are searching for. The search engine looks for the keywords we have entered and returns the results of the search, providing links to relevant Web sites for us to choose from. Some commonly used search engines are MSN, Alta Vista, Google, Yahoo! search and Infoseek etc.



An Operating System is a intermediatery (mediate) between the computer user and computer system. An Operating System is a software program, it is different from word processing programs and spread sheets and all other software programs on your computer.  Mainly the purpose of Operating System is to provide a good environment in which user execute the programs in convenient and efficient manner.
Operating System is main example for system software because software that controls the system hardware that interacts with the user and application software. Today most operating systems perform the following important functions:
1.      Processor management: It manages the assignment of processor to different tasks being performed by the computer system.
2.     Memory management: It manages the allocation of main memory and other storage areas to the system programmes as well as user programmes and data.
3.     Input / Output management: It manages the co-ordination and assignment of different Input and Output devices while one or more programmes are executed.
4.     File management: It allows all files to be easily changed and modified through the use of text editors or some other file manipulation routines.
5.     Establishment and enforcement of a priority system: It determines and maintains the order in which jobs are to be executed in the computer system.
6.     Interpretation of commands and instructions.
7.     Facilitates easy communication between the computer system and the computer operator.
There are Many Operating Systems those have be Developed for Performing the Operations those are requested by the user. The Operating system can perform a Single Operation and also Multiple Operations at a Time. So there are many types of Operating systems those are organized by using their Working Techniques.
1. BATCH PROCESSING:                   Here Batch means collection of instructions. The Batch Processing is same as the Serial Processing Technique. But in the Batch Processing similar types of jobs are firstly prepared and they are stored on the punched card and that card will be submit to the system for the processing. The system then all the operations on the instructions one by one and a user can’t be able to specify any input.
The main problem is that the jobs those are prepared for execution must be the same type and if a job required for any type of input then this will not be possible for the user. And so much of time will be wasted for preparing the Batch wise. Batch processing has been associated with mainframe computers. Commonly uses of batch processing are..
1.      Data processing         2.Printing       3.Images         4.Converting  5.Data base
2. MULTI-PROGRAMMING:            As we know that in the Batch Processing System there are multiple jobs executed by the system. The system first prepare a batch and after that it will execute all the jobs and those jobs are stored into the batch. But the main problem is that if a processor or job requires an input and output operation, then it is not possible and second problem is there will be wastage of the time when we are preparing the batch and  the CPU will remain idle at that time. To overcome this problem another operating system is introduces that is Multiprogramming.
Multiprogramming operating system is one that allows end-users to run more than one program at a time. The technology works by allowing the central processing unit (CPU) of a computer to switch between two or more running tasks when the CPU is idle. The main benefit of this functionality is that it can reduce wasted time in the system's operations. For example, We can open the Ms Word and type a letter and We can hear audio at the same time. We can even make calculations on Ms Excel without closing Ms Word. Thus all these programming can be executed simultaneously by the operating system.
3. MULTIPROCESSING:        Generally a computer has a single processor means a computer have just one CPU for processing the instructions. But if we are running multiple jobs, then this will decrease the speed of CPU. For increasing the speed of processing then we uses the Multiprocessing.
In this multiprocessing there are two or more CPU in a single operating system. If one CPU will fail, then other CPU is used for providing backup to the first CPU. With the help of multiprocessing, we can execute many jobs at a time. All the operations are divided into the number of CPU’s. If first CPU completed his work before the second CPU, then the work of second CPU will be divided into the first and second CPU’s.
4. FILE SHARING:                  File sharing is the public or private sharing of computer data or space in a network with various levels of access privilege. While files can easily be shared outside a network (for example, simply by handing or mailing someone your file on a diskette), the term file sharing almost always means sharing files in a network, even if in a small local area network.
File sharing allows a number of people to use the same file or file by some combination of being able to read or view it, write to or modify it, copy it, or print it. Typically, a file sharing system has one or more administrators. File sharing can also mean having an allocated amount of personal file storage in a common file system. File sharing has been a feature of mainframe and multi-user computer systems for many years. With the advent of the Internet, a file transfer system called the File Transfer Protocol (FTP) has become widely-used.
5. REAL TIME:            A real-time operating system (RTOS) is a system that guarantees a certain capability within a specified time constraint. For example, an operating system might be designed to ensure that a certain object was available for a robot on an assembly line. In what is usually called a "hard" real-time operating system, if the calculation could not be performed for making the object available at the designated time, the operating system would terminate with a failure. In a "soft" real-time operating system, the assembly line would continue to function but the production output might be lower as objects failed to appear at their designated time, causing the robot to be temporarily unproductive.
 Some real-time operating systems are created for a special application and others are more general purpose. To some extent, almost any general purpose operating system such as Microsoft's Windows 2000or IBM's OS/390 can be evaluated for its real-time operating system qualities.
6) TIME SHARING:    A Time Sharing system allows many users to share the computer resources simultaneously. In other words, time sharing refers to the allocation of computer resources in time slots to several programs simultaneously. For example, a mainframe computer that has many users logged on to it. Each user uses the resources of the mainframe i.e. memory, CPU etc.
The Time Sharing system provides the direct access to a large number of users where CPU time is divided among all the users on scheduled basis. The OS allocates a set of time to user. When the time is expired, it passes control to the next user on the system.
Note: Time sharing is no longer commonly used; it has been replaced by multitasking system.

7) MULTI TASKING:  Multitasking is logical extension of multiprogramming system that supports multiple programs to run or execute concurrently. In multitasking more than one task are executed at the same time. In this technique, the multi tasks also known as processes, share common processing resources such as CPU. In the case of a computer with single CPU, only one job can be processes at a time.
For example, when we see someone in the car, next to eating some snacks and taking his cell phone and trying to drive at the same time that person is doing multitasking.
The Serial Processing operating systems   are those which perform all the instructions into a Sequence Manner or the instructions those are given by the user will be executed by using the FIFO manner means First In First Out. All the instructions those are entered first in the system will be executed first and the instructions those are entered later will be executed later. For running the instructions the , the Program Counter is used for executing all the instructions.
In this, the Program Counter will determines which instruction is going to executer and the which instruction will be executer after this. Mainly the punched cards are used for this as input. In this, all the jobs are firstly prepared and stored on the punched card and after that card will be entered in the system and all the instructions will be executed one by one. But the main problem is that a user doesn’t interact with the system while he is working on the system, means the user can’t be able to enter the data for execution.

Network is two or more computers connected logically with the help of data communication devices and transmission media.
The basic purpose of network is communication between two or more machines. Each computer in a network can have its own processing capabilities and can share data files and programs.


There are several different types of computer networks. Computer networks can be characterized by their size as well as their purpose.

The size of a network can be expressed by the geographic area they occupy and the number of computers that are part of the network. Some of the different networks based on size are:
  • Local area network, or LAN
  • Metropolitan area network, or MAN
  • Wide area network, or WAN
Local Area Network: A local area network, or LAN, consists of a computer network at a single site, typically an individual office building. A LAN is very useful for sharing resources, such as data storage and printers. LANs can be built with relatively inexpensive hardware, such as hubs, network adapters and Ethernet cables.
The smallest LAN may only use two computers, while larger LANs can accommodate thousands of computers. A LAN typically relies mostly on wired connections for increased speed and security, but wireless connections can also be part of a LAN. High speed and relatively low cost are the defining characteristics of LANs.

Metropolitan Area Network:  A metropolitan area network, or MAN, consists of a computer network across an entire city, college campus or small region. A MAN is larger than a LAN, which is typically limited to a single building or site. Depending on the configuration, this type of network can cover an area from several miles to tens of miles.

 A MAN is often used to connect several LANs together to form a bigger network. When this type of network is specifically designed for a college campus, it is sometimes referred to as a campus area network, or CAN.

Wide Area Network:   A wide area network, or WAN, occupies a very large area, such as an entire country or the entire world. A WAN can contain multiple smaller networks, such as LANs or MANs. The Internet is the best-known example of a public WAN.


Topology is referred to the way in which the end of a network is linked together.
Network Topology is description of the physical connections of a network or the description of the logical connections between computers of a network indicating which pairs of computers are able to communicate and through which way. There are different types of topologies. They are
1.      Bus Topology    2. Ring Topology    3. Star Topology      4. Star Topology
Bus topology is a network type in where every computer and network device is connected to single cable.

Features of Bus Topology

1.      It transmits data only in one direction.
2.      Every device is connected to a single cable

Advantages of Bus Topology

1.      It is cost effective.
2.      Cable required is least compared to other network topology.
3.      Used in small networks.
4.      It is easy to understand.
5.      Easy to expand joining two cables together.

Disadvantages of Bus Topology

1.      Cables fails then whole network fails.
2.      If network traffic is heavy or nodes are more the performance of the network decreases.
3.      Cable has a limited length.
4.      It is slower than the ring topology.


It is called ring topology because it forms a ring as each computer is connected to another computer, with the last one connected to the first. Exactly two neighbors’ for each device.

Features of Ring Topology

1.      A number of repeaters are used and the transmission is unidirectional.
2.      Date is transferred in a sequential manner that is bit by bit.

Advantages of Ring Topology

1.      Transmitting network is not affected by high traffic or by adding more nodes, as only the nodes having tokens can transmit data.
2.      Cheap to install and expand

Disadvantages of Ring Topology

1.      Troubleshooting is difficult in ring topology.
2.      Adding or deleting the computers disturbs the network activity.
3.      Failure of one computer disturbs the whole network.

In this type of topology all the computers are connected to a single hub through a cable. This hub is the central node and all others nodes are connected to the central node.

Features of Star Topology

1.      Every node has its own dedicated connection to the hub.
2.      Acts as a repeater for data flow.
3.      Can be used with twisted pair, Optical Fiber or coaxial cable.

Advantages of Star Topology

1.      Fast performance with few nodes and low network traffic.
2.      Hub can be upgraded easily.
3.      Easy to troubleshoot.
4.      Easy to setup and modify.
5.      Only that node is affected which has failed rest of the nodes can work smoothly.

Disadvantages of Star Topology

1.      Cost of installation is high.
2.      Expensive to use.
3.      If the hub is affected then the whole network is stopped because all the nodes depend on the hub.
4.      Performance is based on the hub that is it depends on its capacity


It is a point-to-point connection to other nodes or devices. Traffic is carried only between two devices or nodes to which it is connected. Mesh has n (n-2)/2 physical channels to link hn devices.

Types of Mesh Topology

1.      Partial Mesh Topology: In this topology some of the systems are connected in the same fashion as mesh topology but some devices are only connected to two or three devices.
2.      Full Mesh Topology: Each and every nodes or devices are connected to each other.

Features of Mesh Topology

1.      Fully connected.
2.      Robust.
3.      Not flexible.

Advantages of Mesh Topology

1.      Each connection can carry its own data load.
2.      It is robust.
3.      Fault is diagnosed easily.
4.      Provides security and privacy.

Disadvantages of Mesh Topology

1.      Installation and configuration is difficult.
2.      Cabling cost is more.
3.      Bulk wiring is required.


It is the transmission media in which signals are confined to a specific path using wire or cable. The types of Bounded/ Guided are discussed below.


This cable is the most commonly used and is cheaper than others. It is lightweight, cheap, can be installed easily, and they support many different types of network. Some important points :
·         Its frequency range is 0 to 3.5 kHz.
·         Typical attenuation is 0.2 dB/Km @ 1kHz.
·         Typical delay is 50 µs/km.
·         Repeater spacing is 2km.
Twisted Pair is of two types:
·         Unshielded Twisted Pair (UTP)
·         Shielded Twisted Pair (STP)

Unshielded Twisted Pair Cable:

It is the most common type of telecommunication when compared with Shielded Twisted Pair Cable which consists of two conductors usually copper, each with its own color plastic insulator. Identification is the reason behind colored plastic insulation.
UTP cables consist of 2 or 4 pairs of twisted cable. Cable with 2 pair use RJ-11 connector and 4 pair cable useRJ-45 connector.

Advantages :

·         Installation is easy
·         Cheap and high speed capacity,
·         100 meter limit
·         Higher grades of UTP are used in LAN technologies like Ethernet.

Disadvantages :

·         Bandwidth is low when compared with Coaxial Cable
·         Provides less protection from interference.

Shielded Twisted Pair Cable:

This cable has a metal foil or braided-mesh covering which encases each pair of insulated conductors. Electromagnetic noise penetration is prevented by metal casing.

Advantages :

·         Easy to install
·         Performance is adequate
·         Can be used for Analog or Digital transmission
·         Increases the signalling rate
·         Higher capacity than unshielded twisted pair

Disadvantages :

·         Difficult to manufacture
·         Heavy



Coaxial is called by this name because it contains two conductors that are parallel to each other. Copper is used in this as centre conductor which can be a solid wire or a standard one. It is surrounded by PVC installation, a sheath which is encased in an outer conductor of metal foil, barid or both.
Here the most common coaxial standards.
·         50-Ohm RG-7 or RG-11 : used with thick Ethernet.
·         50-Ohm RG-58 : used with thin Ethernet
·         75-Ohm RG-59 : used with cable television
There are two types of Coaxial cables :


This is a 50 ohm (Ω) coaxial cable which is used for digital transmission. It is mostly used for LAN’s. Baseband transmits a single signal at a time with very high speed.


This uses analog transmission on standard cable television cabling. It transmits several simultaneous signal using different frequencies. It covers large area when compared with Baseband Coaxial Cable.

Advantages :

·         Bandwidth is high
·         Used in long distance telephone lines.
·         Transmits digital signals at a very high rate of 10Mbps.
·         Data transmission without distortion.

Disadvantages :

·         Single cable failure can fail the entire network.
·         Difficult to install and expensive when compared with twisted pair.




These are similar to coaxial cable. It uses electric signals to transmit data. At the centre is the glass core through which light propagates.
In multimode fibers, the core is 50microns, and in single mode fibers, the thickness is 8 to 10 microns.
Fiber optic cable has bandwidth more than 2 gbps (Gigabytes per Second)

Advantages :

·         Provides high quality transmission of signals at very high speed.
·         These are not affected by electromagnetic interference, so noise and distortion is very less.
·         Used for both analog and digital signals.

Disadvantages :

·         It is expensive
·         Difficult to install.
·         Maintenance is expensive and difficult.
·         Do not allow complete routing of light signals.


Transmission mode means transferring of data between two devices. It is also called communication mode. These modes direct the direction of flow of information. There are three types of transmission mode. They are:
·         Simplex Mode
·         Half duplex Mode
·         Full duplex Mode


In this type of transmission mode data can be sent only through one direction i.e. communication is unidirectional. We cannot send a message back to the sender. Unidirectional communication is done in Simplex Systems.
Examples of simplex Mode is loudspeaker, television broadcasting, television and remote, keyboard and monitor etc.


In half duplex system we can send data in both directions but it is done one at a time that is when the sender is sending the data then at that time we can’t send the sender our message. The data is sent in one direction.
Example of half duplex is a walkie- talkie in which message is sent one at a time and messages are sent in both the directions.


In full duplex system we can send data in both directions as it is bidirectional. Data can be sent in both directions simultaneously. We can send as well as we receive the data.
Example of Full Duplex is a Telephone Network in which there is communication between two persons by a telephone line, through which both can talk and listen at the same time.
In full duplex system there can be two lines one for sending the data and the other for receiving data.

SOFTWARE:   Software is program or set of instructions which is used to perform a particular task on the computer hardware then it is called as Software. Software can be divided into two major categories. They are
1.      System Software                   2. Application Software
System Software: It is also called as predefined software’s. System software is a one or more programs, designed to control the operation and processing capability of a computer system. It consists of following software’s. They are
1.      Operating System         2. Language Translators         3. Utility Programs
 Utility Programs: These are pre-written programs supplied by the manufacturer for maintaining day to day activities of computer system.                                   Example: COPY, SORT, MAILING, virus scanning software etc.,
Application Software: These are user written programs to do a specific job which can be changed to meet the individual needs. These programs are written in different languages such as BASIC or C or by using database packages like dbase, Oracle.
Example:  Payroll, Billing, Railway Reservation etc. There are two types of application software’s. They are
1.      General software                  2. Special software
General Software: These are developed to suit the needs of research workers / scientists in different fields. These packages are categorized as:
i) Data Analysis   ii) Word Processing iii) Spread Sheet iv) Graphics and v) Databases

VIRUS (Vital Information Resource under Siege) is a software which enters into the computers and attacks other programs or software with a view to damage them.
In general language, a virus is disease inflected in the body. But a computer Virus is a program which is written intentionally by some persons with a view to damage the data, Programs and peripherals.
Characteristics of virus: when a virus is infected to a computer, one or more of the following features
1.      The programs may not work properly or take a lot of time to load.

2.      New messages may be displayed on the screen.

3.      File names may have new characters.

4.      The virus may be spread from one computer to another through network (i.e. internet).
Virus Protection: the steps to virus protection can be divided into two types:
1.      To take precautions to prevent the virus.

2.      To use Anti-virus software.
Precautions to prevent the virus:-
1.      Do not use illegal or pirated software

2.      Do not connect your system with an infected server.

3.      Do not open E-mail attachments coming from unknown persons.
Anti-virus software: - The anti-virus software searches the system for any viruses. There are many Famous anti-virus software’s available in the market. The most famous anti-virus software’s are given below.
1.      Norton PC-cillian
2.      Avast

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