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An input device can be defined as an electromechanical device that allows the user to feed data and instructions into the computer for analysis, storage, and to give the commands to the computer. Data and instructions are entered into the computer’s main memory through an input device. Input device captures data and translates it into a form that can be broadly classified into the following categories:

Key board
A keyboard is the most common input device. Using a keyboard, the user can type the text and execute commands. Keyboard is designed to resemble a regular typewriter with a few additional keys. Data is entered into the computer by simply pressing various keys.
The layout of a keyboard comes in various styles but QWERTY is the most common layout. The layout of the keyboard has changed very little ever since it was introduced. In fact, the most common change in its technology has simply been the natural evolution of adding more keys that provide additional functionality. The number of keys on a keyboard varies from 82 keys to 108 keys. Portable computers such as laptops quite often have custom keyboards that have slightly different key arrangements from a standard keyboard.

Pointing Devices
Pointing devices are the input devices by which we can point out and select the items rapidly from the multiple options displayed on the screen. These devices can also be used to create graphic elements on the screen such as lines, curves and freehand shapes. The most common types of pointing devices available are;
a) Mouse b) Trackball c) Joystick
d) Touch Screen e) Light Pen d) Touch Pad

a) Mouse
A mouse is a small hand-held pointing device, which is used to create graphic elements on the screen such as lines, curves, and freehand shapes. It is also used to run a program and pull down a menu in GUI (Graphic User Interface) base computer system. It is rectangular shaped with a rubber ball embedded at its lower side and buttons on the top. Usually a mouse contains two or three buttons, whish can be used to input commands or instructions. The mouse may be classified into two categories:
I) Mechanical mouse II) Optical mouse

I) Mechanical mouse
A mechanical mouse uses a rubber ball at the bottom surface, which rotates as the mouse along a flat surface to move the cursor. It is the most common and expensive pointing device. Microsoft, IBM and Logitech are some well-known makers of the mechanical mouse.

II) Optical mouse
An optical mouse uses the light beam instead of rotating ball to detect the movement across a specially patterned mouse pad. As the mouse rolls the mouse on a flat surface, the cursor on the screen also moves in the direction of the mouse’s movement. It is more expensive in comparison with the mechanical mouse. Modern optical mouse are accurate and often do not need a mouse pad.

b) Track Ball
A track ball is another pointing device that uses a ball which is settled in a square cardle. In general, a track ball is just like a turned upside down a mouse. The ball is rolled by fingers to move the cursor around the screen. A track ball requires less space than a mouse for operation because the whole device is not moved for moving the curser. It is often attached to or inbuilt into the keyboard. The trackball built into the keyboard are commonly used in laptop computers, because the mouse is not practical for laptop users in a small space. This pointing device comes in various shapes but with the same functionality. It works like a mouse.

c) Joystick
Joystick is a device that moves in all directions and controls the movement of the cursor on the screen. The joystick offers three types of controls.
• Digital control
• Glide control
• Direct control
Digital control allows in a limited movement in a number of directions such as up,
down, left and right. Glid and direct controls allow movements in all directions (360 degree). The basic design of a joystick consists of a stick that is attached to plastic base with a flexible rubber sheath. It has some pushing buttons and a circuit board which is placed under the stick. Joysticks are mainly used for computer games, controlling industrial robots and for other applications such as flight simulators, training simulators, etc.

d) Light Pen
A light pen is a hand-held electro-optical pointing device which is connected to the computer by a cable. When it touches to a connected computer monitor, it will allow the computer to determine where on that screen the pen is pointed. It facilitates drawing images and selects objects on the display screen by directly pointing to the objects with the pen. Light pens give the user the full range of mouse capabilities, without using the pad and any horizontal surface. Using light pens, the user can interact more easily with applications in such modes as dragging and dropping or highlighting. It is very popular for graphic work in engineering like CAD (Computer Aided Design)

e) Touch Screen
A touch screen is a special kind of screen device, which is placed on the computer monitor in order to allow the direct selection or activation of the computer’s information, when somebody touches the screen. Essentially, it registers the input when a finger or other object to touch the screen. Touch screen is normally used to touch the screen. Touch screen is normally used to access the information with minimum effort. However, it is not suitable for input of large amount of data. Typically, they are used in information-providing systems like the hospital, airlines, railway reservation counters, amusement parks, etc.

f) Touch Pad
A touch pad is one of the latest pointing devices. It looks like a small gray window, about two inches wide. It is use din potable computer such as laptop and notebook to substitute the mouse. It has two buttons below or above the pads which work like the mouse buttons. You can move the cursor on the screen by making a finger or other object along the pad .And one can also click by tapping a finger on the touch pad, and drag with a tap in the continuous pointing scale.

Digital Camera
A digital camera is also an input device which stores pictures digitally rather than recording them on a film. Once a picture has been taken that stores on its chip memory. The picture can be downloaded to computer system and then manipulated with an image editing software. Then it can be printed. The major advantage of digital cameras is that making photos is both inexpensive and fast because there is no film processing.

A scanner scans an image and transforms the image to ASCII codes and graphics. This can be edited, manipulated, combined and then printed. Scanners use a light beam to scan the input data. If the data to be scanned is an image, it can be changed by using the special image editing software. If the image is a page of a text, then the special optical character recognition software must be used to convert the image of letters in the text and this can be edited by using a word processor. Most of the scanners come with a utility program that allows it to communicate with the computer and save the scanned image as a graphic file on the computer. Commonly scanners are classified in two types:
• Hand-Held scanner
• Flat-Bed scanner

A microphone is a speech recognition device. Speech recognition is one of the most interactive system to communicate with the computer. The user can simply instruct the computer about the task to be performed with the help of a microphone. It is the technology by which sounds, words or phrases spoken by humans are converted into digital signals, and these signals are transformed into the computer generated texts or commands. Most speech recognition systems are speaker-dependent so they must be separately trained for each individual user. The speech recognition systems system learns to voice of the user, who speaks isolated words repeatedly. Then, these voiced words are recognizable in the future. It is more popular in the corporate world among non-typists, people with disabilities, and business travelers who tap-record information for later transcription.

Graphic Digitizer
Graphic digitizer is an input device, which is used for converting pictures, maps and drawings into digital form for storage in computers. This enables re-creation of the drawing whenever required. It also facilitates any changes in the drawing whenever required.
A digitizer consists of a digital tablet (also known as graphics tablet) associated with a stylus. The digitizing tablet is a flat surface, which contains hundreds of fine copper wires forming a grid. Each copper wire receives electric pulses. The digitizing tablet can be spread over a working table, and is connected to computer.

Optical Scanners
New technologies have developed alternative methods to input data instead of entering data through keystrokes. Devices such as bar code reader can interpret machine printed marks or codes. Accordingly there are four types of optical recognition.
a) OCR (Optical Character Recognition)
b) OMR (Optical Mark Recognition)
c) MICR ( Magnetic-Ink Character Recognition)
d) BCR(Bar Code Reader)

Optical Character Recognition (OCR)
Optical Character Recognition is a process of scanning printed pages as image on a flatbed scanner using OCR software which recognizes the letters as ASCII text. The device used for this technology is called optical reader. In the OCR system book or a magazine article is fed directly into an electronic computer file, and then this file is edited by using a word processor. Advanced OCR systems can read the text large variety of fonts.

Optical Mark Recognition (OMR)
Optical Mark Recognition is the process of recognizing a pre-specified type of marks made by pencils or pen on the paper. This type of technology is used to evaluate the papers of competitive examination. Optical mark reading is done by special device called optical mark reader.

Magnetic-Ink Character Recognition (MICR)
Magnetic-Ink Character Recognition technology is used by the banking industry for faster processing of the large volume of cheques. This technology also ensures accuracy of data entry, because most of the information is pre-printed on the cheque and is directly fed to the computer. Magnetic ink character reader is a device used in the technology.

Bar Code Reader (BCR)
A bar code is a machine-readable code in the form of a pattern of parallel vertical lines. They are commonly used for labeling goods that are available in supermarkets, numbering books in libraries, etc. These codes/strips are sensed and read by a photoelectric device called bar code reader that reads the code by means of reflective light. The information recorded in a bar code reader is fed into the computer, which recognizes the information from the thickness and spacing of bars.



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