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Input Output Devices in Computer System

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Types of Input/Output Devices:

A computer can process the data, so we need some method to input the data into the machine. The devices used will depend on what form this data takes (be it text, artwork etc). Similarly, after processing the data, the result is produced. This result/output could be a display on the computer screen, hardcopy or printed pages or even the audio playback of music.

When we work with the computer we generally /ceil our data and instructions through some devices to the computer. These devices are called input devices.

Computer after processing gives output through other devices called output devices.

Input units are used to input data, information, and instruction into the computer. Whereas output devices are hardware components which are used to generate the output from the computer system. The output can be visual display or print form of the processed information.

Input Devices:

  1. Mouse
  2. Keyboard
  3. Scanner
  4. Touch Screen
  5. Optical Mark Reader (OMR)
  6. Magnetic Ink Character Reader (MICR)
  7. Joystick
  8. Light Pen
  9. Optical Character Reader (OCR)
  10. Bar Code Reader (BCR)

Output Devices:

  1. Printers
  2. Plotters
  3. Monitor
  4. Computer Output Micro Film

Difference between serial and line printer

Serial Printer

Line Printer

  1. Serial printers print only one character at a time.
  2. Example: Dot matrix printer, daisy wheel printer
  3. The serial printer produces a high-quality printout.
  4. They are less durable.
  5. Serial printers are slower than line printer.
  6. They are expensive.
  1. Line printer prints an entire line of text at a time.
  2. Example: Drum printer, Line printer
  3. Line printer produces low    quality    printout.
  4. They are more durable.
  5. Line printers are faster than the serial printer.
  6. They are inexpensive.

Difference between Impact and Non-Impact Printers

Impact Printer

Non-Impact Printer

       1. A printer in which printing is the result of mechanically striking the printing medium.

2. Example: Dot Matrix Printer, Daisywheel Printer.

3. They are noisy.

4. They are slower.

5. They are cheaper.

    1.  Printers that do not strike characters against ribbon or paper, when they print, are non-impact printers.

2.  Example: Ink jet printers, Laser printers.

3.  These printers makes less noise than impact printers.

4. They are faster.

5. They are more expensive than impact printer.

Define LCD along its Advantages and Disadvantages.

An LCD (Liquid Crystal Display) is a flat panel display, video display that uses the right modulating properties of Liquid Crystal.

They are used in a wide range of application, including computer monitor, television, air craft cockpit display etc. They are common in consumer devices such as video players, gaming devices, clocks, watches, calculator, and telephone. LCD has displaced CRT cathode ray tube.

LCD are more energy efficient and offer safer disposal than CRT’s. Its low electrical power consumption enables it to be used in battery-powered electronic equipment. The earliest discovery leading to the development of LCD technology, the discovery of liquid crystal, dates from 1888. By 2008, world-wide sales of television with LCD screen has surpassed the sale of CRT units.

Advantages of LCD:

1.    Very compact and light.

2.    Low power consumption.

3.    No geometric distortion.

4.    Not affected by screen burn in.

5.    Can be made any size or shape.

6.    No high voltage.

Disadvantages of LCD:

1.    Limiting viewing angle, causing color, contrast, and brightness by variations in posture.

2.    Bleeding and uneven backlighting in some monitors, causing brightness distortion especially towards the edges.

3.    Cannot be used with light guns/pens.

4.    Not all LCDs are designed to allow easy replacement of the backlight.

Video Display Unit (VDU) :

Video Display Unit (VDU) is a output device that receives results and other information from the computer and provide them to users. The computer sends information to an output device in the binary form. An output device (VDU) converts it into a suitable form convenient to users such as printed form, display on a screen, voice output, etc. In some applications, the computers output may also be converted by an output unit in the form which can be used as an input to other devices, equipment, machines etc.

Serial Ports:

Computers have a few built-in interfaces called “Ports”. Peripheral devices are interfaced to computer through these ports. Data flow in and out through these ports.

A serial port allows serial data transfer. In serial data transfer, one bit of data is transferred at a time. In the serial interface, only one line or a pair of lines is used to transmit data. It is used for slow speed peripherals such as terminals. The disadvantages of a serial port are that only one device can be connected to a port.

Parallel Port :

A parallel port allows the transfer of all the bits of a word simultaneously. In parallel port interface there are multiple lines to connect the peripheral to the port. A parallel interface is used to transfer data at faster rate for high speed peripherals such as disk and tape. A parallel interface is also known as ‘‘Centronics interface”.

Plasma Display  advantages and disadvantages.

Plasma Display :

Plasma display is a display device that store the image on the screen and allow selective erasing. It is also known as Gas Discharge Display. Plasma contain an array of bulbs. Each bulb can be put into ON and OFF state. Plasma is need not be refreshed. These glass layer are there in plasma panel display. These layer are shown as.


Plasma Display | Allinonetuts

The front layer has vertical strips of grid conductors. The back layer has horizontal strips. The inside surface has a number of holes. It is highly used in a military application for its portable and robust architecture.

Advantages :

  1.   Flat and portable
  2.   Fairly high resolution
  3.   Refreshing not required
  4.   Used in military application

Disadvantages :

  1.   Cost is higher than CRT.
  2.   Not much suitable for animation.
  3.   Slower device.

Optical Scanners :

The optical scanners are capable of reading information recorded on paper, employing light source and light sensors. The following are the commonly used optical scanners :

  • Optical Character Readers (OCR)
  • Optical Mark Readers (OMR)
  • Optical Bar Code Readers (OBCR)

Optical Character Readers (OCR)

An optical character reader detects alphanumeric characters printed or typewritten on paper. It may be a handheld scanner to detect light reflected from a line or from a page of the text. The change in the reflected light is converted to binary data which is sent to the processor. An OCR can scan several thousands printed or typewritten characters per second. OCR are used in large volume applications such as computer oriented bills prepared by public utilities.

Optical Mark Readers (OMR):

Special Marks such as square or bubble are prepared on examination answer sheets. The user fills in these squares or bubbles with soft pencil or ink to indicate their choice. These marks are detected by an optical mark reader and the corresponding signals are sent to the processor.

This method is used where out of a few number of alternatives one is to be selected and marked, for example, market survey, objective type answer sheets and population survey etc.

Optical Bar Code Readers. (OBCR) :

This method uses a number of bars of varying thickness and spacing between them to indicate the desired information. Bar codes are used for most grocery items. An optical bar reader can read such bars and convert them into electrical pulses to be processed by a computer. The most commonly used bar code is universal product code (UPC).

Mouse :

Mouse is the most popular point and draw device. It has become a must have input device on personal computers and workstations which have a Graphical User Interface (GUI) based user interface. A mouse is a small handheld device, which can comfortably fit in a user’s palm. It goals on a small bearing and has one or more buttons on the top. When a user rolls the mouse across the flat surface, the graphic cursor moves on the screen of video display terminal in the direction of the mouses movement depending on the application. The text and graphics cursor may be displayed on the screen at the same time. With a proper software a mouse can also be used to draw pictures on the screen and edit text.

Touch Screen :

Touch screen is the most simple, initiative, and easiest to learn of all input devices. A touch screen enables the user’s to choose from available options by simply touching with their finger the desired icon or menu item displayed on the computer’s screen. Touch screens are the most preferred human-computer interface devices used in information Kiosk. An information Kiosk is an unattended system, which is used to store information of public interest and allows common people to access the stored information as per their requirement.

Joystick :

A joystick is a pointing device, which works on the same principle as a trackball. To make the movement of the spherical ball easier, the spherical ball, which moves in a socket, has mounted on it. Instead of using the fingers in case of a trackball. The user of a Joystick moves the spherical ball with the help of the stick with his/her hand. The stick can be moved forward or backward, left or right, to move and position the graphics cursors at the desired position. Typical uses of a joystick include video games, flight simulators, training simulators and for controlling industrial robots.

Some Input and Output Devices.

Input Devices:

Input devices are necessary to convert our information or data into a form which can be understood by the computer. A good input device should provide timely, accurate and useful data to the main memory of the computer for processing.

Most useful input devices :

1. Keyboard : Keyboard devices are online devices that are used for entering data directly into a computer. Data is entered into the computer by-pressing a set of keys available for these devices. Keyboard devices are becoming more and more popular day-to-day. They are extensively being used today as both input and output devices. Improper use or positioning of a keyboard can lead to repetitive stress injuries.

2. Scanner:  Scanners are basically input devices that are capable or recognising marks or characters. They are used for direct data entry into the computer system. They also eliminate some of the duplication of human effort required to get data into the computer.

3. Mouse : Mouse is an input device that is used with our personal computer. It rolls into a small ball and has two or three buttons on the top. We use mouse because the cursor moves very fast with mouse giving us more freedom to work in any direction. It is easier and faster to move through a mouse.

4. Trackball: Trackball is another pointing device that resembles a ball nestled in a square cradle and serves as an alternative to a mouse. In general, a trackball is as if a mouse is turned upside down. It has a ball which can be rotated by fingers in any direction, the cursor moves accordingly. The size of the ball in the trackball varies from as large as a cue ball, to as small as a marble. Since it is a static device, instead of rolling the mouse on top of the table the ball on the top is moved by using fingers, thumbs and palms.

5.  Light Pen : It is a pen shaped device used to select objects on a display screen. It is quite like the mouse but uses a light pen to move the pointer and select any object on the screen by pointing to the object. Users of Computer Aided Design (CAD) applications commonly use the light pens to directly draw on screen.

Output Devices :

1. Printers :

It is an important output device which can be used to get a printed copy of the processed text or result on paper. There are different types of printers that are designed for different types of application. Depending on their speed and approach of printing, printers are classified as :

(a) Impact Printers : Impact printers use the familiar typewriter approach of hammering a typeface against the paper and inked ribbon.
For example, Dot Matrix Printer.

(b) Non-Impact Printers: Non-impact printers do not hit or impact a ribbon to print. They use electro-static chemicals and inkjet technologies. For example, Laser Printers and Inkjet Printers.

They take the information on our screen and transfer it to paper or a hard copy. The three main types of printers are dot matrix, inkjet, laser printer.

Dot Matrix Printer: Dot matrix printers use small electromagnetically activated pins in the print head, and an inked ribbon, to produce images by the impact.

Inkjet Printer: Inkjet printers work like DMP but fire a stream of ink from a cartridge directly onto the paper.

Laser Printer : Laser printers use the same technology as a photocopier using heat to transfer toner. Laser printer produces goods quality images by the same technology that photocopiers use.

2. Plotters :

Plotter is an important output device, used to print high quality graphics and drawings. Although the graphics can be printed on printers, the resolution of such printing is limited on printers. Plotters are generally used for printing/drawing graphical images such as charts, drawings, maps etc. of engineering and scientific applications.

Plotter | Allinonetuts

Types of Plotter :

Some important types of plotters are as follows :

(a)   Flat Bed Plotters : These plotters print the graphical images by moving the pen on stationary flat surface material. They produce very accurate drawings.

(b)   Drum Plotters : These plotters print graphical images by moving both the pen and the drum having paper. They do not produce as accurate drawings as printed by flat bed plotters.

(c)  Inkjet Plotters : These plotters use inkjets in place of pens. They are faster than flat bed plotters and can print multi-coloured large drawings.

Different types of Printers

Printer :

Printers are the most commonly used output devices that can be found in almost all computer centers. They are the primary output devices used to prepare permanent documents in human readable form (hard copy). Depending on their speed and approach of printing, printers are classified as characters printers, line printers, and page printer. In addition, there is another classification according to which printers are of two types – impact and non-impact.

Impact Printers :

It uses a hammer to hit the ribbon or paper to form the characters or images and mechanism resembles those of typewriter. Example dot matrix, daisy wheel.

1.    Daisy Wheel Printer : These printers use a printwheel font known as a daisy wheel. These printers have print heads composed of metallic or plastic wheels. A raised character is placed on the tip of each of the Daisy character is placed on the tip of each of the daisy wheel ‘petals’. Each petal has an appearance of a letter (uppercase and lowercase) number or punctuation mark on it. To print, the print wheel is rotated around until the desired character is under the print hammer. The petal is then struck from behind by the print hammer, which strikes the character pushing it against the ink ribbon and onto the paper, creating the character.

Daisy wheel printers produce high-resolution output and are more reliable. They can have speeds up to 90 cps. These printers are also called as smart printers because of its bi-directional printing and built-in-microprocessor control features. However, daisy wheel printers give only alphanumeric output. Daisy wheel printers are slower and more expensive than dot matrix printers.

2.   Dot Matrix Printer: Dot matrix printers also known as the wire-matrix printer is the oldest printing technology and its prints one character at a time.
These printers print each character as a pattern of dots. The print head comprises a matrix of tiny needles, typically seven rows with nine needles in each, which hammers out characters in the form of pattern of tiny dots. Usually, dot matrix printers can print shape of character, which a user can 5 aerify. The speed of dot matrix printers are measured in characters per second (cps). The speed can vary from about 200 to over 500 cps. Dot matrix printers are inexpensive and have low operating costs. These printers are able to use different types of fonts, different line densities, and different types of paper. The major limitation of dot matrix printer is that it prints only is black and white.

It’s Features:

  • The print quality of a dot-matrix printer is inferior to that of a daisy wheel printer.
  • DMP is faster than letter quality printer. For example, daisy wheel.
  • Dot matrix printer does not have a fixed character font.

Non-Impact Printers :

They do not hit or impact a ribbon to print. They use thermal, electrostatic and inkjet technologies. For example Inkjet, laser printer.

1. Inkjet Printer : These are non-impact character printer based on relatively new technology. An inkjet printer is a printer that places extremely small droplets of ink onto paper to create an image. Being a non-impact printer, it does not touch the paper while creating an image. Instead it uses a series of nozzles to spray drops of ink directly onto the paper. Inkjets were originally manufactured to print in monochrome (black and white) only. However, the print head has now been expanded and the nozzles increase to accommodate Cyan (C), Magenta (M), Yellow (Y), and Black (K). This combination of colours is called CMYK.

These printers produce high-quality graphics and text printouts. These printers can print about 6 pages a minute and can be programmed to print symbols such as Japanese or Chinese characters.

It’s Features:

  • Inkjet printer produces high-quality output because the character’s are formed by a dozen of tiny ink dots.
  • They are quiet and can form any kind of character.

2. Laser Printer : A laser printer provides the highest quality text and images on personal computers today. It is a very fast printer that uses the same technology as a photocopier using heat to transfer toner. In it laser beams are used to create the image of the document on a drum coated with photo electric material when paper comes in contact with drum, a permanent image is printed on paper with the help of ink. Most laser printers are monochrome.

Laser printers are also known as page printers because they process and store the entire page before they actually print it. They produce sharp crisp images of both text and graphics, providing resolutions from 300 to 1200 dpi. They are quiet and fast, able to print 4-32 text only page per minute for individual microcomputers. These printers are useful for volume printing because of their speed.

Working of Input devices.

Mouse :

Mouse is an important input device. The mouse is a palm-size device with a ball built into the bottom. The mouse may be mechanical or optical and comes in many shapes and sizes. When we move the mouse over a smooth surface, the balls rolls, and the pointer on the display screen moves in the same direction. It is used to move cursor, draw sketches or diagrams, selecting a text or object or menu item etc. With the mouse, we can draw, select options from a menu and modify or move text. We can give commands by pointing with the pointer and clicking a mouse button. In addition to minimizing typing errors, a mouse makes operating a microcomputer easier for beginning users.

Working Of Mouse :

Principally, the mouse works by measuring how much it moves in a given direction. A mechanical mouse has a rubber ball at the bottom. When the user moves the mouse, the balls rolls along the surface of the mouse pad, and the mouse keeps track of how far the ball rolls. Inside the bottoms of the mouse are three rollers – one of them, the one mounted at 45° angle to the other two is spring loaded. This roller is usually the smallest of the three. The other two rollers are usually larger and of different colour. These rollers are mounted at a 90° angle to one another, one roller measures how fast the ball is turning horizontally and the other measures how fast it is turning vertically. When the ball rolls, it turns these two rollers. The rollers are connected to axles, and the axles are connected to a small sensor that measures how fast the axle is turning. Both sets of information are passed to the electronics inside the mouse. This little processor, usually consisting of little more than a single chip, uses the information to determine how fast the mouse itself is moving and in what direction. This information is passed to the computer via a mouse cord, where the operating system then moves the pointer accordingly.

Keyboard :

Most input data is entered into the computer by using a keyboard. This input method is similar to typing on a typewriter.

Computer keyboards include keys that are designed to perform specific tasks. These special keys include function keys, directional keys and special-purpose keys such as Alt, Ctrl, Enter, Ins, and Esc. These keys enable the user to perform complex tasks easily when using the application. For example, many applications use a function key to access online help for the user. Some new keyboards have even 110 keys, with three new keys designed to simplify working with Windows 95. Two of these keys, next to the Alt key, bring up the Start menu. The third key, next to the right Ctrl key, brings up a menu of functions that are frequently accessed in whichever application is currently being used.

Working of Keyboard :

A keyboard is a series of switches connected to a small keyboard microprocessor that monitor the state of each switch and initials a specific response to a change in state. When the user presses a key, it causes a change in the amount of current flowing through the circuit associated specifically with that key. The keyboard microprocessor detects this change in current flow. By doing this, the processor can tell when a key has been pressed and when it is being released. Depending upon which key’s circuit carries a signal to the microprocessor, the processor generate the associative code, known as
‘Scan code’ of the key and sends it to the operating system. A copy of this code is also stored in the keyboard’s memory. When the operating system reads the scan code, it informs the same to the keyboard and the scan code stored in keyboard’s memory is then erased.

Scanner :

The scanner is widely used in Desktop Publishing (DTP) applications. It is used for digitizing images such as photograph, forms, documents etc into the computer. Some of the scanners also read the text by converting the typed pages into word processing files. Graphics scanners convert a printed image into video image without converting it to digital code.

Working Of Scanner:

When the hand-held scanner’s scan button is pressed, a light emitting diode illuminates the document underneath it. An inverted angled mirror directly over the scanner’s window reflects the image onto the scanner’s lens which is located on the backs of the scanner. The lens focuses a single line of the image onto a charged coupled device (CCD) which contains a row of light detectors. As the light shines through these detectors, each of them records the amount of light as a voltage that corresponds to white, black and gray to a color. These voltages are sent to a specialized analog chip which corrects any color detection error. After that, a single line image is passed to analog to digital counter (ADC) which converts the analog signals into binary forms that can be sent to the computer. In this way, the converter clears itself of the data so that it can receive the next line of the image.

Touch Screen:

The touch screen is the most simple, initiative, and easiest to learn of all input devices. A touch screen enables the user’s to choose from available options by simply touching with their finger the desired icon or menu item displayed on the computer’s screen. Touch screens are the most preferred human-computer interface devices used in information Kiosk. An information Kiosk is an unattended system, which is used to store information of public interest and allows common people to access the stored information as per their requirement.

Working of Touch Screen:

A rasic touch screen has 3 main components a touch sensor, a controller, and a software driver. The touch sensor/panel is a clear glass panel with i touch responsive surface. It is placed over a display screen so that the responsive area of the panel covers the viewable area of the video screen. The two most famous touch screen techniques are infrared beams and ultrasonic acoustic waves. The infrared beams interlace the surface of the screen and when a light beam is broken, that particular location is recorded. On the contrary the ultrasonic acoustic waves pass over the surface of the screen and when the wave signals are interrupted by some contact with the screen, the location is recorded.

The panel generally has an electrical current going through it and touching the screen causes a voltage change which is used to determine the location of ihe touch to the screen. The controller connects the touch sensor and the computer. It takes information from the touch sensor and translates it into information that a computer can understand.

Light Pen:

A light pen is a pointing device. It is used to select a displayed menu option on the Cathode Ray Tube (CRT). It is a photosensitive pen like device. It is capable of sensing a position on the CRT screen when its tip touches the screen. When its tip is moved . over the screen surface, its photocell sensing element detects the light coming from the screen and the corresponding signals are sent to the processor.

A light pen can also be used for graphics work. A user can draw directly on the CRT screen with the light pen if the computer system is provided with Computer Aided Design (CAD) package.


Light Pen | Allinonetuts

Working of Light Pen:

The light pen, with its interface and software, makes a time measurement that is translated into X-Y coordinates representative of a position on the monitor. The light pens contain a lens and a photo
detector located at its tip. When the electron beam that sweeps the monitor strikes the phosphor within the light pen’s field of view, the light emitted by the phosphor is focused through the lens and onto the photo detector. The position of the beam is tracked by the horizontal and vertical counted, which relay this information to a register. This cycle is repeated for every frame produced by the electron beam. By noting when a scan goes by the measuring the interval between scan lines or entire screen refreshes an accurate position of the photo detector on the screen is determined. The light pen software generates x-y vectors corresponding to a point on the screen, which may be used to make a selection by activating a switch on the light pen.

Trackball :

The trackball is another pointing device that resembles a ball nestled in a square cradle and serves as an alternative to a mouse. In general, a trackball is as if a mouse is turned upside down. It has a ball which can be rotated by fingers in any direction, the cur- a moves accordingly. The size of the ball in the trackball varies from as large as a cue ball, to as small as a marble. Since it is a static device, instead of rolling the mouse on top of the table the ball on the top is moved by using fingers, thumbs, and palms.

Working of Trackball:

A trackball consists of a number of components. As one moves the trackball, it starts a chain of events inside the box that results in the pointer moving on the computer screen. In a normal trackball, on one side of each encoding wheel is a pair of Light Emitting Diode that emits infrared light. On the opposite side of each pair of LEDs, there is a light sensor. Every time light from the LEDs shines through a hole in the encoding wheel, a pulse of electricity is sent from the light sensor to the microprocessor. When the trackball rolls side-to-side, the horizontal (x-axis) shaft rotates, spinning the attached encoder wheel. Similarly, when the trackball is rolled up and down, the vertical (y-axis) shaft rotates, spinning the attached encoder wheel. Due to this spinning, the light blinks which can be detected by the light sensor. The microprocessor counts how many times the light sensors detect light each second and send this information to the computer along with the cord.