computer fundamental and devices

8/8/2019 computer fundamental and Devices

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Explain the input devices?

Input devices are used to capture the data and transmit it to thecomputer system for further processing and in computer readableform. Some of the input devices are as under.

Keyboard Devices:

Keyboard devices are the most commonly used devicestoday.

They are used for data entry into a computer system bypressing a set of keys , which is connected to a computersystem.

Programs and data are entered into a computerthrough a keyboard .

A keyboard is similar to a typewriter it containsAlphabets, digits, special charters and some controlkeys.

When a key is pressed an electrical signal is producedwhich is detected by an electronic circuit called keyboardencoder.

Its function is to detect which key has been pressed andsend binary code for it.

What is scanner?

Data scanning devices are input devices, which are usedfor direct entry into the computer system from sourcedocuments. Data Scanning Devices are of many types:

Image Scanner:

An Image scanner is an input device ,Which translates paper documents into an electronicformat Which can be stored in a computer

The Input document may be text, pictures and evenhandwritten material.

The copy of a document stored in a computer and can be


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displayed or printed whenever desired .

Two common used types are:

Flatbed Scanner:

A Flatbed Scanner is like a copy machine , which consistsof box having glass plate on the top.

The document to be scanned is placed upside down onthe glass plate the light is below the glass plate and moveshorizontally from left to right when activated.

After scanning one line the light beam moves up alittle and scans a next line.

This process is repeated for all the lines.

Hand-held scanner:

A Hand-held scanner to scan a document, the scanner is

slowly dragged from one end of the document toits other end with its lights on. The scanner has to be dragged very carefully over the

document. Otherwise the conversion of the document into its equivalent

bitmap will not be correct due to this reason hand-heldscanners are used only in cases where high accuracy is notneeded.

They also much cheaper as compared to flatbed scanners. When image scanners are used for inputting text documents,

they have the following limitations :

Input document is stored as an image , instead of text. The computer can't interpret the stored document asnumbers characters and special symbols. The storage required for storing the documents


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as an image is much more than that required forstoring the same document as a text .

Point-and-Draw Devices:Mouse:

Mouse is the most popular point-and-draw device today. A mouse is also called a pointing device. It moves across a flat surface with the help of tracking balls. Its movement and the direction of the movement are detected by two

rotating wheels on the underside of the mouse called sensors.

Light Pen:A Light pen is a pointing device. It is used to select and write the text on theCRT. It is capable of sensing a position on the CRT screen when its tip touchesthe screen.

Joystick: A Joystick is also a pointing device . It is used to move the cursor position on the CRT screen. Its function is similar to that of a mouse . It is a stick which has spherical ball at its lower-end as well as

its upper-end. The lower spherical ball moves a socket. The joystick can be moved right or left, forward and backward. Mainly used in playing 3D games. On most joysticks, a button on the top is provided to select the

option .

Touch Screen: A Touch screen enables the users to choose from available options by


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simply touching with their fingers the desired icon or menudisplayed on the computer screen .

Touch screens are mostly preferred human-computer interfacedevices used in information kiosks.

Which is used to store information of public interests Allows common people to access the stored information as per their

requirements? Example: At an Airport or a railway station to provide information to arriving

passengers about hotels, tourist sports etc. in the city. In large museums it guides about various attractions and facilities.

OCR (Optical Character Reader):

The OCR technology is used to overcome these limitations. In this, the scanner is equipped with character reorganization software

called OCR software. This software first creates the bitmap image of the document and then the OCR software translates it into ASCII text,which the computer can interpret as letters, numbers and specialcharacters.

If the document contains Italics or Boldface letters or fonts other thanthat for which the OCR software has been designed, the OCR softwarewill not work efficiently.

Output Devices:An output device accepts data from a computer and translates them into aform, which is suitable for use by the outside world. Output devices can bebroadly classified into the following categories:

1. Monitors

1. Printers2. Plotters3. Screen Image Projector4. Voice Response Systems

1. Monitors:


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Monitors are the most popular output devices used today forproducing soft-copy output.

A monitor is usually used with a keyboard, and together they formvideo display terminals (VDT).

It serves as both input/output devices. The two basic types of monitorsare Cathode-ray-tube (CRT) and flat-panel.

The CRT monitors look much like a television; on the other hand, theflat panel monitors are thinner and lighter and are commonly used withportable computer systems like notebook computers.

Printers:

Printers are the most commonly used output devices for producing

hard-copy output . The various types of printers are:

Dot-Matrix Printers:

Dot-Matrix printers are character printers, which print one characterat a time.

They print the characters and all kinds of images as a pattern of dots .

A dot-matrix printer has a print head , which can move horizontallyacross the paper.

The print head contains an array of pins , which can be activatedindependent of each other and strike against an inked ribbon toform a patter of dots on the paper .

To print a character, the printer activates the appropriate set of pins asthe print head moves horizontally.

Dot-Matrix printers are impact printers because they print byhammering the pins on the inked ribbon to leave ink impressions onthe paper.

Due to impact printing, dot-matrix printers are noisy as compared tonon-impact printers.

Dot-matrix printers are normally slow with speeds rangingbetween 30 to 600 characters per second.


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Ink jet Printers:

Ink jet printers are character printers , which form characters and allkinds of images by spraying small drops of ink on to the paper .

The print head of an ink jet printer has 64 tiny nozzles , When the register heats up, the ink near it vaporizes, and is ejected

through the nozzle, and makes a dot on the paper placed in front of theprint head.

To print a character , the printer selectively heats the appropriateset of nozzles as the print head moves horizontally.

Inkjet printers produce higher quality output than dot-matrixprinters.

Inkjet printers produce printed output as patterns of tiny dots . They can print any shape of characters which a programmer can

describe. Inkjet printers can not be used to produce multiple copies of a

document in a single printing. Inkjet printers are slower than dot-matrix printers with speeds

ranging between 40 to 300 characters per second. An Inkjet printer is more expensive than a dot-matrix printer. Costly.

Drum Printers:

Drum printers are line printers , which print one line at a time. It has solid drum with characters embossed on its surface in the

form of circular bands. Each band consists of all the printing characters supported by the

printer in its character set. The printer has a set of hammers mounted in front of the drum in a

manner that an inked ribbon and paper can be placed betweenthe hammers and the drum.

The drum rotates at the high speed and a character at a printposition is printed by activating the appropriate hammer.

The drum of a printer is expensive and can't be changed often.Costly.

Typical speed of drum printers is in the range of 300 to 2000 linesper minute.


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Laser Printers:

Laser printers are page printers , which print one page at a time . The main components of a laser printer are a laser beam

source . To print a page of output the laser beam is focused on the electro

statically charged drum by the multi sided mirror. It uses the electro static charging technique . The mirror focuses the laser beam on the surface of the drum in a

manner to create the patterns of the characters/images to be printedon the page.

Laser beam move on the drum with the paper and thecharacter and the images will be printed on the paper.

The toner then permanently fused on the paper with heat and pressureto generate the printed output.

The drum is then rotated and cleaned with rubber blade to remove thetoner sticking to its surface to prepare the drum for the next pageprinting.

Laser printer produces very high quality output. They have high resolution and because of their high resolution these

printers give excellent graphics art quality. They can print any shape which a programmer can describe. Laser

printers can not be used to produce the multiple copies of a singledocument in a single printing.

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