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Showing posts from March, 2017

Types of Computer

Computers can be broadly classified by their speed and computing power.
Sr.No.TypeSpecifications1PC (Personal Computer)It is a single user computer system having moderately powerful microprocessor2WorkStationIt is also a single user computer system which is similar to personal computer but have more powerful microprocessor.3Mini ComputerIt is a multi-user computer system which is capable of supporting hundreds of users simultaneously.4Main FrameIt is a multi-user computer system which is capable of supporting hundreds of users simultaneously. Software technology is different from minicomputer.5SupercomputerIt is an extremely fast computer which can execute hundreds of millions of instructions per second. PC (Personal Computer)A PC can be defined as a small, relatively inexpensive computer designed for an individual user. PCs are based on the microprocessor technology that enables manufacturers to put an entire CPU on one chip. Businesses use personal computers for word processing…

Computer - Fifth Generation

Computer - Fifth GenerationThe period of fifth generation is 1980-till date. In the fifth generation, the VLSI technology became ULSI (Ultra Large Scale Integration) technology, resulting in the production of microprocessor chips having ten million electronic components. This generation is based on parallel processing hardware and AI (Artificial Intelligence) software. AI is an emerging branch in computer science, which interprets means and method of making computers think like human beings. All the high-level languages like C and C++, Java, .Net etc., are used in this generation.
AI includes:
RoboticsNeural NetworksGame PlayingDevelopment of expert systems to make decisions in real life situations.Natural language understanding and generation. The main features of fifth generation are:
ULSI technologyDevelopment of true artificial intelligenceDevelopment of Natural language processingAdvancement in Parallel ProcessingAdvancement in Superconductor technologyMore user friendly …

Computer - Fourth Generation

Computer - Fourth Generation The period of fourth generation was 1971-1980. The computers of fourth generation used Very Large Scale Integrated (VLSI) circuits. VLSI circuits having about 5000 transistors and other circuit elements and their associated circuits on a single chip made it possible to have microcomputers of fourth generation. Fourth generation computers became more powerful, compact, reliable, and affordable. As a result, it gave rise to personal computer (PC) revolution. In this generation time sharing, real time, networks, distributed operating system were used. All the high-level languages like C, C++, DBASE etc., were used in this generation.
The main features of fourth generation are:
VLSI technology usedVery cheapPortable and reliableUse of PC'sVery small sizePipeline processingNo A.C. neededConcept of internet was introducedGreat developments in the fields of networksComputers became easily available Some computers of this generation were:

Computer - Third Generation

Computer - Third Generation The period of third generation was 1965-1971. The computers of third generation used integrated circuits (IC's) in place of transistors. A single IC has many transistors, resistors and capacitors along with the associated circuitry. The IC was invented by Jack Kilby. This development made computers smaller in size, reliable and efficient. In this generation remote processing, time-sharing, multi-programming operating system were used. High-level languages (FORTRAN-II TO IV, COBOL, PASCAL PL/1, BASIC, ALGOL-68 etc.) were used during this generation.
The main features of third generation are:
IC usedMore reliable in comparison to previous two generationsSmaller sizeGenerated less heatFasterLesser maintenanceStill costlyA.C neededConsumed lesser electricitySupported high-level language Some computers of this generation were:
IBM-360 seriesHoneywell-6000 seriesPDP(Personal Data Processor)IBM-370/168TDC-316

Computer - Second Generation

Computer - Second Generation The period of second generation was 1959-1965. In this generation transistors were used that were cheaper, consumed less power, more compact in size, more reliable and faster than the first generation machines made of vacuum tubes. In this generation, magnetic cores were used as primary memory and magnetic tape and magnetic disks as secondary storage devices. In this generation assembly language and high-level programming languages like FORTRAN, COBOL were used. The computers used batch processing and multiprogramming operating system.
The main features of second generation are:
Use of transistorsReliable in comparison to first generation computersSmaller size as compared to first generation computersGenerated less heat as compared to first generation computersConsumed less electricity as compared to first generation computersFaster than first generation computersStill very costlyA.C. neededSupported machine and assembly languages Some computers o…

Generations of Computers

The history of computer development is often in reference to the different generations of computing devices. Each of the generation of computers is characterized by a major technological development (switching technology)that fundamentally changed the way computers operate. Most major developments resulted in increasingly smaller, cheaper and more powerful and efficient computing devices. The evolution of computers are categorized in five generations:
1st Generation (Vacuum Tube)2nd Generation (Transistor)3rd Generation (Integrated circuit)4th Generation (VLSI)5th Generation (ULSI, Parallel Computing, Artificial Intelligence) Computer - First GenerationThe period of first generation was 1946-1959. The computers of first generation used vacuum tubes as the basic components for memory and circuitry for CPU (Central Processing Unit). These tubes, like electric bulbs, produced a lot of heat and were prone to frequent fusing of the installations, therefore, were very expensive and c…


CRT stands for Cathode Ray Tubes and is the very old style display which uses the florescent blue tube in itself and it projects the electrons to the screen at a time. These projections are responsible for creating the images on the screen. These monitors are pretty heavy and have been configured for some various sizes. In CRT there is vacuum glass tube under which Electron gun shoots beam of electrons toward the back of monitor screen
It is coated with chemical dots called phosphors glow when electrons strike themBeam of electrons scans the monitor from left to right, and top to bottom in a raster pattern to create the image.Trio of dot phosphors is grouped in triangle for each hardware picture elementElectron beam returns regular to each phosphor to sustain the glow.More dots better qualityDot pitch Measurement between the same spot in two vertically adjacent dot triosExpressed in millimeters or dots per inchDot pitch tells “sharpness”Software-pixel placement is limited to hard…

Display Devices

A display device or VDU (Video Display Unit) is an output device for presentation of information in visual. When the input information is supplied has an electrical signal, the display is called an electronic display.
Common applications for electronic visual displays are televisions or computer monitors.
All of the PCs that we use need to have some displays. Normally there are the standard monitors, but they now are available in various varieties like LCD, LED. The evolution of the displays has not just only made the space that they contain become less, but also has made them more efficient.

Common Terms

Pixel: In digital imaging, a pixel, pel, dots, or picture element is a physical point in a raster image, or the
smallest addressable element in an all points addressable display device; so it is the smallest controllable element of a picture represented on the screen. The address of a pixel corresponds to its physical coordinates. LCD pixels are manufactured in a two-dimensiona…

Laser Printer

Laser printers are non impact printers work on the principle of static electricity i.e. atoms with opposite charges attract each other. The computer or digital camera sends the matter to be printed to the printer. This information is converted into dots by an internal processor. The most important part of the printer is the photoreceptor , a revolving drum which is made of photoconductive material. This drum is given a positive charge. A laser beam is shot at it when there is a dot making that area negatively charged. The laser beam remains off when there is blank space. This is now exposed to laser toner which is positively charged. The positively charged toner pigments get attracted to the negatively charged areas of the electric drum. With one complete rotation, the drum is now covered with the required image. Next the print media , say a paper, which is negatively charged is passed over the drum. The positively charged toner pigments now get attracted to the paper and th…

Inkjet Printer

An inkjet printer is non impact printer. It a computer peripheral that produces hard copy by spraying ink onto paper. A typical inkjet printer can produce copy with a resolution of at least 300 dots per inch ( dpi ). Some inkjet printers can make full color hard copies at 600 dpi or more. Many models include other devices such as a scanner , photocopier , and dedicated fax machine along with the printer in a single box.
In the inkjet printing mechanism, the print head has several tiny nozzles, also called jets. As the paper moves past the print head, the nozzles spray ink onto it, forming the characters and images. An inkjet printer can produce from 100 to several hundred pages, depending on the nature of the hard copy, before the ink cartridges must be replaced. There is usually one black ink cartridge and one so-called color cartridge containing ink in primary pigments (cyan, magenta, and yellow). Some inkjet printers use a single cartridge with cyan, magenta, yellow, and bl…

Line Printers (Drum and Chain Printer)

Line Printers: They are known as line printers because they print one line at a time. Characteristics of a line printer:

Characters are raised on the drum or chain.Different fonts cannot be used for printing.High printing speed and quality. There are two types of line printers: Drum printers and chain printers.

Drum Printers: In a drum printer characters are raised in a cylindrical drum. Values of all characters are stored in the printer buffer. When a character has to be printed, the printer sends the information to printer buffer.  Then, printer drum is rotated and when the code match is done the character is printed by striking the hammer.  There is a carbon ribbon in between the drum hammer and paper.  So, when the hammer strikes an impression is produced in the paper.

Chain Printers: Instead of a drum, chain with raised characters is used in these types of printers. Values of all characters are stored in the printer buffer. When a character has to be printed, the printer …

Daisy Wheel Printer

A daisy wheel printer is an early type of impact Printer invented in 1969 by David S. Lee at Diablo Data Systems. The printer uses a metal or plastic disk containing each of the letters, numbers, and other characters it supports. When something is printed, the printer rotates the disk to each character and then using a hammer strike each character into an ink ribbon to create the character on paper.

Daisy wheel printers were popular in the 1970s and 1980s, but are no longer used because of they have a low quality of print, are very slow, loud, and laser printers have come down in cost.

1) It can print letter quality characters.


1) Printing speed is slow.
2) It cannot print graphics.

Dot Matrix Printer

A Dot Matrix Printer or Impact Matrix Printer refers to a type of computer printer with a print head that runs back and forth on the page and prints byimpact, striking an ink-soaked cloth ribbon against the paper, much like a typewriter. Unlike a typewriter or daisy wheel printer, letters are drawn out of a dot matrix, and thus, varied fonts and arbitrary graphics can be produced. Because the printing involves mechanical pressure, these printers can create carbon copies and carbonless copies. Each dot is produced by a tiny metal rod,also called a "wire" or "pin", which is driven forward by the power of a tiny electromagnet or solenoid, either directly or through small levers (pawls). Facingthe ribbon and the paper is a small guide plate pierced with holes to serve asguides for the pins. The moving portion of the printer is called the print head,and when running the printer as a generic text device it generally prints one lineof text at a time.
Most dot matrix printer…


Printers are Output devices used to prepare permanent Output devices on paper. 
Device that prints text and graphics in the same format and shape which is displayed on the screen connected via printer cable or USB cable.Transforms digitally stored documents, graphics, text data on paper/hard copy.Speed of printer is measured in printed pages per minute.Printers can be shared in the LAN, Wireless networks or Ethernets.New types of printers are combined with printing, scanning and fax in a single unit.Printers can be divided into two main categories :
Impact Printers : In this hammers or pins strike against a ribbon and paper to print the text. This mechanism is known as electro-mechanical mechanism. They are of two types.
(i) Character Printer (ii) Line Printer Character Printer : It prints only one character at a time. It has relatively slower speed. Eg. Of them are Dot matrix printers. 
Line Printer : It prints one complete line at a time. Eg. Of them are Drum printers. 

Non-Impact Pr…

Recognition Devices

Character and mark recognition devices are scanners that are able to recognize special characters and marks. Essentially used for certain applications. Types MICR (Magnetic Ink Character Recognition): Used by banks to read numbers written on cheque.Special purpose machine reads character made of ink containing magnetized particles.

OCR (Optical Character recognition): Special preprinted characters that can be read by light source and changed into machine readable form.Used in department stores to read retail price tags by reflecting light.

OMR (Optical Mark Recognition): An OMR device senses the presence or absence of a mark such as pencil mark.Used to calculate or store multiple choice tests.

Bar Code Reader

An electronic device used for reading printed bar codes.Consists of light source, lens, and light sensor for translating optical impulses into electrical ones.Also consists of decoder circuitry to analyze the barcode image data provided by sensor.This bar code identifies the product to the supermarket computer which has latest description and price.Computer automatically tells the electronic cash register the price.These are easy to use and widely used in electronic shops and malls.

Output Devices

An output device is any device used to send data from a computer to another device or user. Most computer data output that is meant for humans is in the form of audio or video. Thus, most output devices used by humans are in these categories. An output device is any peripheral that receives data from a computer, usually for display, projection, or physical reproduction.Examples include monitors, projectors, speakers, headphones and printers.

Output of processed data can be divided into two classes: Hard Copy Output that is in the form of print document, which can be read directly, long last and permanently stored. E.g. A word document containing text and images printed by the printer on a paper. Soft Copy Output that is in the form of metallic or audio form, which is cannot be read directly by the user. E.g. A collection of music files and folders on a CD. Accordingly the output devices are classified as hard copy devices and soft copy devices. Hard Copy Devices : printers, fax m…

Mouse, Joystick, Light pen

Mouse 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. Mouse can be used to control the position of cursor on screen, but it cannot be used to enter text into the computer.
AdvantagesEasy to useNot very expensiveMoves the cursor faster than the arrow keys of keyboard.
Joystick 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 Li…

Input Devices

Those means or devices by which we feed data (any type) to computer. These devices have capability to convert that data in digital form i.e. in 0 & 1. Also known as peripherals and computer hardware.
Following are few of the important input devices which are used in a computer:
KeyboardMouseJoy StickLight penTrack BallScannerGraphic TabletMicrophoneMagnetic Ink Card Reader(MICR)Optical Character Reader(OCR)Bar Code ReaderOptical Mark Reader(OMR) Keyboard Keyboard is the most common and very popular input device which helps in inputting data to the computer. The layout of the keyboard is like that of traditional typewriter, although there are some additional keys provided for performing additional functions.
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.
The keys on the keyboard are as follows:
Sr.NoKeysDescription1Typing KeysThese keys include the letter keys (A-Z) and digit keys (0…