Input and Output Devices

By Suresh Chand

 Important Questions

The unit which is used to supply data into a computer is called input devices.Those devices which are used to input data into computer and retrieve data from computer is called input/output (I/O) devices.These I/O devices provide the environment of communication between the computer and outer the world.These I/O devices are called peripheral devices.for example:-keyboard, mouse, scanner, monitor, printer etc are I/O devices.

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Input Devices:

1. Keyboard:

Keyboard is an input device with various keys that enables you to enter data into computer. computer keyboard are similar with electric typewriter except consisting extra additional keys. keyboard consists following types of keys:

  1. Alpanumeric keys:-Letters, and numbers
  2. Punctation keys:-comma, period, semicolon and so on.
  3. Special keys:-function keys, control keys, arrows keys cap lock key, and so on.

There are different types of keyboard having different number of keys.for example the original PC keyboard has 84 keys,AT keyboard has also 84 keys,similarly the enhanced keyboard has 101 keys.other keyboard consists  up to 104 keys.

2. Mouse

The device that control the movements of cursor or pointer on a display screen is called mouse. A mouse is a small object that you can roll along a hard flat surface. As you move the mouse the pointer on the display screen moves in the same direction. Mouse consists one to three button which have different function as required.

Types of mice

There are three types of mouse:

A) Mechanical Mouse:

This type of mouse has a rubber or metal ball on its underside that roll in all directions. Mechanical sensors within the mouse detect the direction the ball is rolling and move the screen pointer accordingly.

B) Opt mechanical Mouse:

Same as mechanical mouse but it uses optical sensor to detect motion of the ball.

C) Optical mouse:

This type of mouse uses laser beam (special light) to detect the mouse’s movement. Optical mouse has no mechanical moving parts; optical mouse removes the drawback of mechanical mouse. So that they respond more quickly and precisely than mechanical and opt mechanical mice but they area also more expensive than other mice.

Mouse Connection

Mice use three methods to connect PC’S-

  • serial mice connect directly to an RS-232, SERIAL PORT or PS/2 port.This is the simplest type of connection.
  • bus mice connect to the bus through an interface card. This is some what more complicated because you need to configure and install an expansion board.
  • cordless mice are not physically connected at all. Instead they rely on infrared or radio waves to communicate with the computer.

3) Trackball:

Track ball is similar to mouse except that it requires less space than mice. When space is limited trackball is used to move the pointer you have to rotate the ball with your thumb, fingers or the palm of your hand. Due to limited space in LAPTOP computer, track ball is used instead of mouse. There are usually one to three buttons on trackball. Trackball is popular than mice because it is stationary so it does not require much space and we can place it into any type of surface.

4) Joystick:

A joystick is a pointing device which is often used for playing compute games. The joystick has gearshift like lever that is used to move the pointer on the screen. On most joysticks a button on the top is used to select option. it is used to control robots. With a joystick the pointer continues moving in the direction the joystick pointing, to stop the pointer you must return the joystick to its upright position.

5) Digitizing tablet:

This is an input device that enables you to enter drawing and sketches into a computer. A digiting tablet consists of an electronic tablet and a cursor or pen. Then cursor is similar to mouse except that it has a window with cross hairs for pinpoint placement and it can have as many as 16 buttons. The pen is also called a stylus and looks like a simple ballpoint pen but uses an electronic head instead of ink. The tablet contains electronics that enables it to detect the movement of the cursor or pen and translate the movements into digital signals that it sends to the computer.

For digiting tablet each point on the tablet represents a point on the display screen in a fixed manner. The static nature of digitizing tablets makes them particularly effective for tracing drawings. Digitizing tablets are also called digitizers, graphics tablets, touch tablets or simply tablets.

5) Scanner:

A scanner is an input device that can read text and transfer from a piece of paper into computer represent able. To do this the scanner sends a beam of light to the page and then measures the amount of light reflected back. A scanner works by digitizing an image –dividing it into a grid of boxes and representing each box with either zero or a one, Depending on weather the box is filled in. Each box is represented by 24 bits, the resulting matrix of bits called a bit map, can stored in a file displayed on a screen and manipulated by programs.

6) Digital Camera

Digital camera is used to input image into computer. Digital camera uses the digital photographic technology. Normal camera capture images on specially coated film whereas digital cameras capture images electronically. then it sends images as digital data into computer.

7) Magnetic ink character Reader (MICR):

MICR is that type of device which reads text printed using magnetic ink. MICR devices were developed to help the banking field in processing the large volumes of cheques. The MICR devices is used automatically to read cheque number, bank identification code and customer account number. MICR is used to read those number and character which are made with magnetic materials.

8) Optical Character Reader:

OCR is the ability of machine to recognize characters.OCR is a type of optical scanner, which can detect alphanumeric characters printed on paper. The OCR uses special light, or optic to read text from a piece of paper. A special font standard is needed to recognize character. The OCR system consist combination of hardware and software to recognize characters. The advanced OCR system can read variety of fonts, but still have difficulty to read hand written text.

The OCR devices examine each character by analyzing point of characters then when the whole character is scanned, it is compared with standard fonts in which OCR devices are programmed to recognize the optical characters.  OCR is used for large volume processing application such as reading of passenger tickets, processing motor vehicles registration etc.

10) Bar Code Reader:

Bar code Reader also called as bar code scanner is a input device that uses laser beams to read bar codes on products such as books, packages. so it is used in supermarkets, bookshops etc.

The bar code reader can identify the description of product items and latest price.

11) Touch Screen:

This is easiest way to enter data using the finger touch. Touch screens enables the user to select an option by pressing a specific part of the screen. Touch screen is a type of display screen that has a touch sensitive transparent panel covering the screen. Touch screen enables us to directly select objects instead of using pointing devices such as mouse, light pens. Touch screen are commonly used in fast food restaurants and information centers.

12) Touch Pad:

Many Laptop computers use a touch pad in front of the keyboard. We can move our fingers on the pad to move the cursor on the screen. When we want to click, we can tap pad or use the buttons front of the pad, which works like mouse buttons.

13) Light Pen:-light pen is used as pointing device, which is very sensitive to light. It uses a light-sensitive detector to select objects on display screen. A light pen is similar to mouse except that with a light pen you can move the pointer and select objects on the display screen by directly pointing to objects with the pen. Now a days light pens are used in big hotel’s room for the customer for selecting their choice of menu and other items.

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Output Devices:

An ouput device is a machines which accept data from a computer and translates as a result or information which is suitable for use by the outside the world (users).

There are two types of output generated by output devices:

a) Soft-Copy Output:

A soft-copy output is an output, which is not produced on paper or some materials. So it can’t be touched and carried for being shown to others. for example: output seen on display screen.

b) Hard-Copy Output:

A hard copy output is an output which is produced on paper or some materials, which can be touched and carried for beings shown to others. These types of output are permanent in nature and can be kept in paper files, or can be looked later when the person is not using the computer. For examples output produced by printers or plotters are hard copy output.

Types of output Devices

1) Monitor

Monitor is called visual display unit (VDU) and it is also called display screen .The user can sees their result on the monitor screen. Monitor gives soft copy output. Computer monitor are similar with television screens except that monitor are extremely flexible and reliable devices.

The two basic types of monitors used are Cathode Ray Tube (CRT) and LCD(Liquid Crystal Display).The CRT monitor look much like television and are used with non-portable computer system. On the other hand LCD monitor are thinner and lighter are commonly used with portable computer systems like laptop and notebook computers.

Classification of monitor Based on Signals.

Monitors accept either analog or digital signal from video adapter. so there are two types of monitor based on signals.

A) Digital Monitor:- 

A digital monitor accepts digital signals rather than analog signals. All monitors (except LCD) use CRT technology, which is essentially analog. The term digital therefore refers only to the type of input received from the video adapter. Then digital monitor then translates the digital signals into analog signals that control the actual display. Thus digital monitors are fast and produce clear images.

B) Analog Monitor:

This is the traditional type of color display screen that has been used for years in televisions. So in reality all monitors based on CRT technology ((that is all monitors except LCD) are analog.

Characteristics of a monitor

A) Size:

The size shows type of screen based on size example 14 inch, 17 inch etc.

B) Resolution:

The resolution of monitor is expressed by the number of pixels on the screen, expressed as a matrix. The resolution refers to the number of dots displayed in the x (across) and y (down) co-ordinates. The resolution of a monitor indicates how densely the pixels are packed. Pixel is short for picture Element; a pixel is a single point in graphic image. The quality of display monitor largely depends on its resolution, for example a resolution of 800×600 means that there are 800 pixels in horizontally and 600 pixels in vertically.

C) Band Width:

The Bandwidth refers the amount of data that can be transmitted in a fixed amount of time. Thus this determines how much data it can process and therefore how fast it can refresh at higher resolution. For digital computer it is expressed in bits or byte per second (bps) and for analog it uses hers (HZ).

D) Refresh Rate:

Refresh rate refers to the number of times per second that the image is redrawn on the monitor screen. i.e. Refresh rate means how many times per second the screen is refreshed(redrawn).Display monitors must be refreshed many times per second. The refresh rate for a monitor measured in hertz(Hz).The faster the refresh rate ,the less monitor flickers.

2) Printer:

Printers are one of the main output devices. it gives hard copy output. The output we get  through this device is called as hardcopy or hard output. Printers are classified into two categories on speed.

Impact Printer Non-Impact Printer
Produces characters and graphics on a piece of paper by striking it is called impact printer. A type of printer that produces characters and graphics on a piece of paper without striking.
It prints by hammering a set of metal pin or character set. Printing is done by depositing ink in any form.
Electromechanical devices are used No electromechanical device is used.
Faster speeds around 250 words per second. Slower speeds around 1 page per 30 seconds.
Have banging noise of needle on paper Works silently
Dot-matrix printer, Daisy wheel printers, line printer are examples . inkjet printers, photo printers, laser printers are examples .

A) Impact Printers:

1) Daisy-Wheel printer:

Daisy-wheel printer has a plastic or metal wheel on which the shape of each character stands out in relief. A hammer presses the wheel against a ribbon, which in turn makes an ink stain in the shape of the character on the paper.Daisy-wheel printer’s produces letter-quality type.

Daisy –wheel printers are noisy and slow and can print from 10 to 75 characters per second.This type of printers can not print graphics.

2) Dot-Matrix printer:

Dot-matrix printer produces character by striking pins against an ink ribbon.Each pin makes a dotm and combination of dots form characters.print head is a type of these printers which consists of a matrix of tiny needles,typically seven rows with nine needles in each(9*7 matrix).

Dot- matrix printer are inexpensive and relatively fast (can print 50 t0 500cps) and noisy also.

B) Non-impact printers

1) ink-jet printer:

Ink-jet printer is called non-impact printer because they print by spraying ink on paper and ,which print characters by spraying small drops of ink at a sheet of paper. The ink is different from normal ink having a high iron content. There are magnetized plates in the ink’s path which direct the ink onto the paper in the desired shapes. Ink-jet printers can also print in high  color, which makes them popular for home users. Although ink-jet printers are inexpensive and produce excellent output, they are slow. But it can not be used to produce multiple copies of a document in a single printing.

2) Laser printer:

Laser printers work like photo copy machines. laser printer uses laser beam to produce image. Laser printer can produce very high quality print and are capable of printing an almost unlimited variety of fonts. The light of laser alters the electrical charge on the drum wherever it hits. These charges attract toner, which is transferred to the paper and fussed to the surface by a heat process. laser printer are faster and more expensive than others. The Laser print quality is measured in number of dots per inch(dpi) i.e. The Best laser printer can produce 600dpi or more.


3) Plotter

A plotter or graph plotter is a device used to output graphics on output medium like paper. This device provides completely different form of output and have a variety of applications. outputting graphics means plotting(drawing) shapes of graph, bar charts, pie charts, maps etc. They produce line by pen, and more expensive than printers and widely used for engineering applications.

Sound card and speakers: sound card is an output device which is related with production of sound in the computer system. An expansion board that enables a computer to manipulate and output sounds.

A connection point that acts as interface between the computer and external devices like mouse, printer, modem, etc. is called port. Ports are of two types −

  • Internal PortIt connects the motherboard to internal devices like hard disk drive, CD drive, internal modem, etc.
  • External PortIt connects the motherboard to external devices like modem, mouse, printer, flash drives, etc.

Let us look at some of the most commonly used ports.

most commonly used ports | CSIT Guide

Serial Port:

Serial ports transmit data sequentially one bit at a time. So they need only one wire to transmit 8 bits. However it also makes them slower. Serial ports are usually 9-pin or 25-pin male connectors. They are also known as COM (communication) ports or RS323C ports.

Parallel Port:

Parallel ports can send or receive 8 bits or 1 byte at a time. Parallel ports come in form of 25-pin female pins and are used to connect printer, scanner, external hard disk drive, etc.

USB Port:

USB stands for Universal Serial Bus. It is the industry standard for short distance digital data connection. USB port is a standardized port to connect a variety of devices like printer, camera, keyboard, speaker, etc.

PS-2 Port:

PS/2 stands for Personal System/2. It is a female 6-pin port standard that connects to the male mini-DIN cable. PS/2 was introduced by IBM to connect mouse and keyboard to personal computers. This port is now mostly obsolete, though some systems compatible with IBM may have this port.

Infrared Port:

Infrared port is a port that enables wireless exchange of data within a radius of 10m. Two devices that have infrared ports are placed facing each other so that beams of infrared lights can be used to share data.

Bluetooth Port:

Bluetooth is a telecommunication specification that facilitates wireless connection between phones, computers and other digital devices over short range wireless connection. Bluetooth port enables synchronization between Bluetooth-enabled devices. There are two types of Bluetooth ports −

  • Incoming− It is used to receive connection from Bluetooth devices.
  • Outgoing− It is used to request connection to other Bluetooth devices.



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