Computer Peripheral

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  • Input Devices

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

a) Keyboard Devices:
keyboard devices are the most commonly used devices today. They allow data entry into a computer system by pressing a set of keys, which is connected to a computer system. Programs and data are entered into a computer through a keyboard. A keyboard is ?? similar to a typewriter it contains Alphabets,digits,special chars and some control keys.
When a key is pressed an electrical signal is produced which is detected by an electronic circuit called keyboard encoder. Its function is to detect which key has been pressed and send binary code for it.

b) Point-and-Draw Devices:

  • Mouse:

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

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


3. Trackball:
A Trackball is a pointing device, similar to a mouse. The ball
is placed in the base of a mouse, is placed on the top along with the buttons. To move the cursor around the screen the ball is rolled with the fingers. because the whole device is not moved. The cursor is often attached to or built into the keyboard. Trackballs built into the keyboard are commonly used in laptop(notebook) computers. because a mouse is not practical for laptop users in a small place.
A Trackball comes in various shapes with the same functionality. The commonly used shapes are a ball, a button and a square. In case of a button, the button is pushed with a finger in the desired direction. In the case of a ball, the ball is rolled with the help of fingers to move the cursor.

4. 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.

5. Touch Screen:
A Touch screen enables the users to choose from available options by simply touching with their fingers the desired icon or menu displayed on the computer screen. Touch screens are mostly preferred? human-computer interface devices used in information kiosks. Which is used to store information of public interests and allows common people to access the stored information as per their requirements.

            • ??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.

c) Data scanning Devices:
Data scanning devices are input devices, which are used for direct entry into the computer system from source documents. Data Scanning Devices are of many types:

1. Image Scanner:
An Image scanner is an input device, which translates paper documents into an electronic format which can be stored in a computer. The Input document may be text, pictures and even handwritten material. The copy of a document stored in a computer and can be displayed or printed whenever desired.
Two common used types are:

a) Flatbed Scanner:
A Flatbed Scanner is like a copy machine, which consists of ? box having glass plate on the top. The document to be scanned is placed upside down on the glass plate the light is below the glass plate and moves horizontally from left to right when activated. ??? After scanning one line the? light beam moves up a little and scans a next line. This process is repeated for all the lines.



? b) Hand-held scanner:
A Hand-held scanner to scan a document, the scanner is ????? slowly dragged from one end of the document to its 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-held scanners are used only in cases where high accuracy ?? is not needed. They also much cheaper ass 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 as numbers characters and special symbols.
  • The storage required for storing the documents as an image is much more than that required for storing the same document as a text.


? 2) 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 special characters. If the ??? document contains Italics or Boldface letters or fonts other than that for which the OCR software has been designed, the OCR software will not work efficiently.


3) OMR (Optical Mark Reader):
These scanners are capable of recognizing a type of mark made by pencil or pen. For example, in many exams there is a objective type test in which they had to mark their answers darkening a small square by a pencil. These answer sheets are directly fed to a computer for grading with the use of an optical mark reader.

4) Bar-code Reader:
Data coded in the form of small lines are known as bar codes. Bar codes represent alphanumeric data by a combination of vertical lines by varying their width and spacing between them. They are particularly used for unique identification of all types of goods and products.
Hand-held scanner scans a bar-code image and converts it into an alphanumeric value, which is then fed to the computer to which the bar-code reader is attached.
The first 5 of digits identify the manufacturer or supplier of the product and the next 5 digits identify a specific product of the manufacturer.

5) Magnetic-Ink Character Reorganization (MICR):
MICR is similar to OCR, and used by the banking industry for faster processing of the large volume of cheques. This cheques are special type of cheque includes bank?s identification code, account no and the cheque no are pre-printed using special characters with a special ink which contains magnetizable particles of iron oxide.
When a customer presents a filled-in cheque at a bank, a bank employee manually enters the amount written on the cheque, the date of transaction. Using an MICR reader the MICR reads the data or takes it for further processing processes this cheque. This cheque also ensures accuracy of data entry because most of the information is pre-printed on the cheque and this is directly fed to the computer.

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


  • Printers
  • Plotters
  • Screen Image Projector
  • Voice Response Systems

? ? ?Output devices generates computer output, which can be classified into the following two types:

    • Soft-copy Output:

A soft-copy output is an output, which is not produced on a paper or some material, they are temporary in nature, and vanish after use. For example, output displayed on a terminal screen or a spoken out by a voice response system is a soft-copy output.

    • Hard-copy Output:

A Hard-copy output is an output, which produced on some paper or material, which can be touched and carried out for being shown to others. They are permanent in a nature and can be kept in paper files, or it can be looked later, when the person not using the computer.

1. Monitors:
Monitors are the most popular output devices used today for producing soft-copy output. A monitor is usually associated with a keyboard, and together they form a video display terminals (VDT). It serves as both input/output devices. The two basic types of monitors are Cathode-ray-tube (CRT) and flat-panel. The CRT monitors look much like a television; on the other hand, the flat panel monitors are thinner and lighter and are commonly used with portable 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 character at a time. They form the characters and all kinds of images as a pattern of dots. A dot-matrix printer has a print head, which can move horizontally across the paper. The print head contains an array of pins, which can be activated independent of each other and strike against an inked ribbon to form a patter of dots on the paper. To print a character, the printer activates the appropriate set of pins as the print head moves horizontally.
Dot-Matrix printers are impact printers because they print by hammering the pins on the inked ribbon to leave ink impressions on the paper. Due to impact printing, dot-matrix printers are noisy as compared to non-impact printers. Dot-matrix printers are normally slow with speeds ranging between 30 to 600 characters per second.

  • Ink jet Printers:

? Ink jet printers are character printers,which form characters and all kinds of images by spraying small drops of ink on to the paper. The print head of an ink jet printer contains upto 64 tiny nozzles, which can be selectively heated up in a few microseconds by an integrated circuit register. 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 the print head. To print a character, the printer selectively heats the appropriate set of nozzles as the print head moves horizontally.
Inkjet printers produce higher quality output than dot-matrix printers. 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.

  • ?Drum Printers:

Drum printers are line printers, which print one line at a time. It consists of a solid drum with characters embossed on its surface in the form of a 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 between the hammers and the drum. The drum rotates at the high speed and a character at a print position is printed by activating the appropriate hammer. The drum of a printer is expensive and can't be changed often. Typical speed of drum printers are in the range of 300 to 2000 lines per minute.


  • Chain/Band Printers:

?? Chain/band printers are line printers, which print one line at a time. It consists of a metallic chain/band on which all the characters of the character set supported by the printer are embossed. The Printer has a set of hammers mounted in front of the chain/band in a manner that an inked ribbon can be placed between the hammers and the chain/band.
The chain/band rotates at a high speed,and a character at a print position is printed by activating the appropriate hammer. Just like drum printers, chain/band printers can only print pre-defined set of characters, which are embossed on the chain/band. Due to this reason, chain/band printers do not have the ability to print any shape of characters and different types of graphics. Speed of? the chain/band printer are in the range of 400 to 3000 lines per minute.

  • 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. 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 printed on the page. The toner then permanently fused on the paper with heat? and pressure to generate the printed output. The drum is then rotated and cleaned with rubber blade to remove the toner?? sticking to its surface to prepare the drum for the next page printing. Laser printer produce 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 single document in a single printing.

3) Plotters:
Dot matrix, Inkjet and laser printers are capable ?? of producing graphics? output, However many ?? engineering design applications, like architectural plan

of building, designing of a mechanical component of a car require high-quality. Then we used special type of output device, called plotters, is used for this ??? purpose. Plotters are an ideal output device for architects, engineers, city planners.

4) Screen Image Projector:
Screen image projector is an output device, which is used to project information from a computer on to a large screen (such as a cloth screen or a wall), so that can be simultaneously viewed by a large group of ??? people. This output device is very useful for making presentations to a group of people with the direct use ? of a computer. It can directly plugged to a computer system, and the presenter can make a presentation to a group of ?? people by projecting the material one after another on a large screen with the help of a computer's keyboard or mouse. Screen Image projectors have become a common presentation equipment today.

5) Voice Response Systems:
Voice response system enables a computer to talk to a user. A voice response system has an audio-????? response device, which produces audio output. The ?? output is temporary, soft-copy output.Voice response system is of type:

a) Voice Reproduction System:
A Voice reproduction system produces audio output by selecting an appropriate audio output from a set of pre-recorded audio responses. The set of pre-recorded audio responses may include ?? words, phrases or sentences spoken by the human beings. The Analog recordings of the pre-recorded sound are first ?? converted into digital data and then permanently ?? stored on the computer disk.
Voice reproduction systems are very useful in a ??? wide range of applications.

  • Banking Industry uses voice reproduction system in Automatic Teller Machine to provide systematic guidance to customers on how to transact with the bank by using an ATM.
  • Automatic Answering Machines. For example, telephone inquiries for new telephone numbers in place of an old number , or vacancy status of a particular flight or train is often taken care of by an automatic answering machine.
  • Video games are made exciting and interesting by playing an event-based sound from a set of pre-recorded sound.
  • Talking alarm clocks. For example every hour the clock speaks out what the time by selecting the appropriate voice message corresponding to that hour from the set of pre-recorded voice messages else the clock may speak ?its time to wake up? at the set for alarm.

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