Input Units

A computer consists of an I/O system. This system includes two basic components, one is I/ O device and other called I/O Module. A device which is connected to an I/O module of computer is called a peripheral.

The data entry station or devices are termed as input units. Example: keyboard, mouse, scanner, joystick, joypad, graphics table, MICR etc.


(a) Keyboard:

The keyboard is a standard input device. It is a data entry platform of computer. The layout of the keyboard is like that of traditional QWERTY typewriter, although some extra command and function keys are provided for internet, multimedia, operating system and software operation. It has small processor attached to a visual display unit.



The processor checks for the accuracy of data at the time of entry. When key is pressed, electrical signal is generated which determine which key was pressed. This process is termed as encoding.

Some types of standard keyboard:

(i) XT (Extended Techno10gy):83 keys

(ii) AT (Advanced Technology):101 keys

(iii) Enhanced Technology: 103 keys

In apple Macintosh, ABD keyboard is used. It is connected to Apple Desktop Bus (ADB). Some input devices are: scanner, mouse, MICR, OMR, OCR, OBR, Light pen, touch pad etc.


 (b) Mouse:

  • Mouse is a point and click input device with two or three buttons.
  • The first mouse was built in 1968 by Douglas Engelbart at Stanford Research Institute. This mouse is bulky and made from wood piece with two gear wheels. In beginning “bug” term is used for mouse, but it is replaced by term mouse very soon. The shape of modern mouse is designed by engineer and watchmaker Andre Guignard.
  • Apple built the first single button mouse in 1982 for GUI (Graphic User Interface) of his products. The Doug Englebart is known as inventor of Mouse.


There are many technology applied in designing of mouse. The optical mouse is based on laser technologies. Scroll wheel has facilities to scroll page upward and downward direction.


(c) Scanner:

Scanner is an input device. It is used to enter pictures, graphs and other documents in computer and allow saving in different formats. It has main two components:

  • Data capturing sub system: is used to illustrate image and convert into optical form.
  • Image Processing Subsystem: is used to convert optical image into digital.


Its resolution varies from 72 ppi (pixel per inch) to 2400 ppi. Black and white and color scanners are available in market in reasonable cost. The cost depends on resolution image into digital.

Types of scanner:

  • Flatbed Scanner or Desktop Scanner: are the most versatile and commonly used scanners. In fact, this article will focus on the technology as it relates to flatbed scanners.
  • Sheet-fed Scanner: are similar to flatbed scanners except the document is moved and the scan head is immobile. A sheet-fed scanner looks a lot like a small portable printer.
  • Handheld Scanner: Use the same basic technology as a flatbed scanner, but rely on the user to move them instead of a motorized belt. This type of scanner typically does not provide good image quality. However, it can be useful for quickly capturing text.
  • Drum Scanner: are used by the publishing industry to capture incredibly detailed images. They use a technology called a photo-multiplier tube (PMT). In PMT, the document to be scanned is mounted on a glass cylinder. At the center of the cylinder is a sensor that splits light bounced from the document into three beams. Each beam is sent through a color filter into a photo-multiplier tube where the light is changed into an electrical signal.

(d) Joystick:

The joystick is originally from the field of aviation, where it refers to the control stick used by a pilot to control the flight of the plane. As such it is mainly used for interaction with computer games, in particular flight simulators. It consists of a lever, or stick, which is moved by the user and transmits these movements to the computer. It also normally has additional buttons or switches that are used in addition to the stick.



(e) Joypad:

Similar to a joystick, the joypad is designed for gaming input. In many ways it is identical to the joystick, with the main difference being the use of a multi-directional touch pad in place of the stick.

It is most commonly used with games consoles, but also suitable for computers. More recent models also have analogue control sticks, used as miniature joysticks. The ergonomics of the device are also different, with the pad designed to be held with both hands.

(f) Graphics Table:

A flat rectangular pressure sensitive input device, where a stylus or similar pointing device is used on its surface. The position of the stylus is translated into the onscreen co-ordinates of the pointer. Most commonly used for graphics design and engineering work, or other programs where a more precise form of input is required from the user. It is connected to serial port of computer.

(g) MICR:

It stands for Magnetic Ink Character Recognition. The human readable characters are printed on documents using a magnetic ink. In 1966, two standards of MICR fonts were accepted by International Standards Organization: E13B (USA) and CMC8 (France, and other European countries).

The main limitation of MICR is that only the 10 digits and 4 special characters needed for bank processing are used. No alphabetic characters are available. Special type of magnetic ink is required for encoding the characters to be read by the machine.

(h) OCR:

It stands for Optical Character Recogniti0n/ Reader. It reads printed characters directly and converts them into appropriate codes and stores them in a computer. When light source is passed over a document the written or typed characters reflect less light than the background area. Thus the shape of characters may be determined. Each character is scanned several times and an electronic picture of it is built up. If the characters are typewritten, they must be typed in OCR-font. The standard fonts used are OCR-A (American Standard) and OCR-B (European Standard).

(i) OBR:

It stands for Optical Bar Code Reader. It scans a set of vertical bars of different width for specific data and are used to read tags. In USA, each grocery Product has been given a unique 10-digits codes that are represented bar codes form on every products. Bar code Reader is a device used for reading (encoding) bar-coded data.

Bar-code reading is performed by a laser-beam scanner which is stroked across the patterns of bits that is recorded as the input data. The most widely known bar code is the Universal Product Code (UPC) which now appears on almost all retail package in U.S.A. The first five of these digits identify the manufacturer or supplier of the product and the second five digits identify a specific product of manufacturer. Bar code reading is done by a light pen or scanner connected to a computer.

(j) Voice Reorganization Device:

The voice reorganization device is an input device used to instruct and feed data to computer through voice. The data is fed through microphone, which converts sound into electrical signal, and electrical signal of sound is matched with patterns available in pattern dictionary of computer. If sound (electrical signal) is matched, data is processed and output is generated. IBM has developed a Talkwritter with 6000 words with 95% accuracy for business correspondence.

It is helpful for bedridden, handicapped persons to input data in the form of voice. Voice response devices range from mainframe audio-response units to voice messaging minicomputers to speech synthesizer microprocessors. Speech microprocessors can be found in toys, calculators, appliances, automobiles, and a variety of other consumer, commercial, and industrial products. .

(k) Touch screen:

The touch screen is a modern and advance technology applied in wrist watch, camera, pager etc. It is a screen with touch sensitive points or program icons. When specific point or icon is touched by finger tips, related program or prompts are activated.



There are three types of touch sensitive screen technology:

  • Capacitive Screen: made from capacitors. When screen is touched with a stylus or finger, capacitors generate sense in the form of charge to computer.
  • Infrared screen: It contains infrared emitter (Light Emitting Diode) and infrared receptor cell( photo detector cell). When screen is touched, the emitted beam of light is interrupted sense the position of finger or pressure.
  • Pressure sensitive screen: Screen is made from Mylar plastic sheet which under side contains rows of invisible net of wires. Each sheet is separated with each other and if one sheet has horizontal net of wires, next has vertical fashion of net of wires. When screen is touched the wires at that point make contact and circuit is closed. This is sensed and feed to the computer.

(l) Light Pen:

Light pen is an input pointing device used to draw diagram on VDU directly. It is connected with VDU. The tip of pen contains light sensitive element (LED), which, when placed against the screen, detects the light from the screen enabling to computer to identify the location of the pen on the screen.

The pen operates on two cell batteries span of 8 months if used for 30 minutes daily. It is used in engineering drawing, architect design, circuit design and other several graphics and art works. It is also used as pointing device for menu displayed on VDU (Visual Display Unit) like as mouse. The menu item is pointed by point of pen, and button is clicked.

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