Computer Peripherals

• I/O Devices

  • Provide means of communication between a computer and outer world
• Commonly Used Input Devices

  • Keyboard devices
  • Point-and-draw devices
  • Data scanning devices
  • Digitizer
• Keyboard Devices


  • Allow data entry into a computer system by pressing a set of keys (labeled buttons) neatly mounted on a keyboard connected to a computer system
  • 101-keys QWERTY keyboard is most popular
• Point-and-Draw Devices


  • Used to rapidly point to and select a graphic icon or menu item from multiple options displayed on the Graphical User Interface (GUI) of a screen
  • Used to create graphic elements on the screen such as lines, curves, and freehand shapes
  • Commonly used devices: mouse, trackball, joystick, light pen, touch screen
• Mouse


  • Commonly used in personal computers and workstations
• Trackball


  • Commonly used in laptop (notebook) computers
• Joystick


  • Commonly used for video games, fight simulators, training simulators, and for controlling industrial robots
• Electronic Pen


  • Pen-based point-and-draw device
  • Used to directly point with it on the screen to select menu items or icons or directly draw graphics on the screen
• Touch Screen


  • Most simple, intuitive, and easiest to learn of all input devices
• Data Scanning Devices


  • Enable direct data entry into a computer system from source documents
  • Eliminate the need to key in text data into the computer
  • Improve data accuracy and increase the timeliness of the information processed
  • Demand high quality of input documents
  • Some devices are capable of recognizing marks or characters
  • Form design and ink specification usually becomes more critical for accuracy
• Image Scanner


  • Translates paper documents into an electronic format for storage in a computer
• Optical Character Recognition (OCR) Device


  • Scanner equipped with character recognition software that converts bit map images of characters to equivalent ASCII code
  • Standard OCR fonts: OCR-A (American standard), OCR-B (European standard)
• Optical Mark Reader (OMR)


  • Scanner capable of recognizing a pre-specified type of mark by pencil or pen
• Bar-code Reader


  • Scanner used for reading barcodes
• Electronic Pen


  • Very useful for grading tests with objective type questions, or for any input data that is of a choice or selection nature
• Bar-code Reader


  • Scanner used for reading (decoding) bar-coded data
  • Universal Product Code (UPC) is the most widely known bar coding system
• Magnetic-Ink Character Recognition (MICR)


  • MICR is used by banking industry for faster processing of large volume of cheques
• Digitizer


  • Input device used for converting (digitizing) pictures, maps and drawings into digital form for storage in computers
  • Commonly used in the area of Computer Aided Design (CAD) by architects and engineers to design cars, buildings, medical devices, robots, mechanical parts, etc.
  • Used in the area of Geographical Information System (GIS) for digitizing maps available in paper form
• Electronic-card Reader


  • Electronic cards are small plastic cards having encoded data appropriate for the application for which they are used
• Speech Recognition Devices


  • Input device that allows a person to input data to a computer system by speaking to it
• Types of Speech Recognition Systems

  • Single word recognition systems can recognize only a single spoken words, such as YES, NO, MOVE, STOP, at a time. Speaker-independent systems are mostly of this type
  • Continuous speech recognition systems can recognize spoken sentences, such as MOVE TO THE NEXT BLOCK. Such systems are normally speaker-dependent
• Vision-Input Systems


  • Allow computer to accept input just by seeing an object
• Commonly Used Output Devices

  • Monitors
  • Printers
  • Plotters
  • Screen image projector
  • Voice response systems
• Soft-copy output is not produced on a paper or some material that can be touched and carried for being shown to others. It is temporary in nature and vanishes after use
• Types of Output

  1. Soft-copy output: Not produced on a paper or some material that can be touched and carried for being shown to others. Temporary in nature and vanish after use. Examples are output displayed on a terminal screen or spoken out by a voice response system

  2. Hard-copy output: Produced on a paper or some material that can be touched and carried for being shown to others. Permanent in nature and can be kept in paper files or can be looked at a later time when the person is not using the computer. Examples are output produced by printers or plotters on paper
• Commonly Used Output Devices

  • Monitors
  • Printers
  • Plotters
  • Screen image projector
  • Voice response systems
• Monitors


  • They are the most popular output devices used for producing soft-copy output. Display the output on a television-like screen. A monitor associated with a keyboard is called a video display terminal (VDT), which is the most popular I/O device
• Types of Monitors

  • Cathode-ray-tube (CRT) monitors look like a television and are normally used with non-portable computer systems. Flat-panel monitors are thinner and lighter and are commonly used with portable computer systems like notebook computers. Now they are also used with non-portable desktop computer systems because they occupy less table space
• Dot-Matrix Printers


  • They are character printers that form characters and all kinds of images as a pattern of dots.
• Inkjet Printers


  • They are character printers that form characters and all kinds of images by spraying small drops of ink onto the paper. They can print many special characters, different sizes of print, and graphics such as charts and graphs. They are non-impact printers, hence they cannot produce multiple copies of a document in a single printing. They can be both monochrome and color. They are slower than dot-matrix printers with speeds usually ranging between 40 to 300 characters per second. They are more expensive than a dot-matrix printer
• Drum Printers


  • They are line printers that print one line at a time. They have a solid cylindrical drum with characters embossed on its surface in the form of circular bands. They are impact printers and usually monochrome. Typical speeds are in the range of 300 to 2000 lines per minute
• Chain/Band Printers


  • They are line printers that print one line at a time. They can only print pre-defined sets of characters that are embossed on the chain/band used with the printer. They cannot print any shape of characters, different sizes of print, and graphics such as charts and graphs. They are impact printers and can be used for generating multiple copies by using carbon paper or its equivalent. They are usually monochrome. Typical speeds are in the range of 400 to 3000 lines per minute
• Laser Printers


  • They consist of a laser beam source, a multi-sided mirror, a photoconductive drum, and toner (tiny particles of oppositely charged ink). Laser printers produce very high-quality output having resolutions in the range of 60
• Typical speeds

  • 400 to 3000 lines per minute
• Laser Printers


  • Consist of a laser beam source, a multi-sided mirror, a photoconductive drum, and toner
  • Produce high-quality output with resolutions in the range of 600 to 1200 dpi
  • Can print special characters, different sizes of print, and graphics
  • Non-impact printers
  • Monochrome, but color options available
  • Low-speed printers can print 4 to 12 pages per minute, very high-speed printers can print 500 to 1000 pages per minute
  • More expensive than other printers
• Plotters


  • Ideal output device for architects, engineers, city planners, etc.
  • Two types: Drum plotter and Flatbed plotter
• Screen Image Projector


  • Output device for projecting information from a computer onto a large screen
  • Useful for making presentations with multimedia content
• Voice Response Systems


  • Enables computer to talk to a user
  • Two types: Voice Reproduction System and Speech Synthesizer
• Voice Reproduction Systems


  • Produce audio output by selecting pre-recorded audio responses
  • Applications include guiding how to operate a system, automatic answering machines, video games, etc.
• Speech Synthesizers


  • Convert text information into spoken sentences
  • Used for reading out text to blind persons, aiding communication for those who cannot speak, translating text into spoken words