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. Following are the most useful input devices.
Keyboard: This is the standard input device attached to all computers. The layout of keyboard is just like the traditional typewriter of the type QWERTY. It also contains some extra command keys and function keys. It contains a total of 101 to 104 keys. A typical keyboard used in a computer is shown in Fig. 2.6. You have to press correct combination of keys to input data. The computer can recognize the electrical signals corresponding to the correct key combination and processing is done accordingly.
Mouse: Mouse is an input device shown in Fig. 2.7 that is used with your personal computer. It rolls on a small ball and has two or three buttons on the top. When you roll the mouse across a flat surface, the cursor on the screen moves in the direction of mouse movement. The cursor moves very fast with mouse giving you more freedom to work in any direction. It is easier and faster to move through a mouse.
Trackball: Trackball is another pointing device. Essentially, a trackball is a mouse lying on its back. To move the pointer, you rotate the ball with your thumb, your fingers, or the palm of your hand. There are usually one to three buttons next to the ball, which you use just like mouse buttons.
The advantage of trackball over mouse is that the trackball is stationary so it does not require much space to use it. In addition, you can place a trackball on any type of surface, including your lap. For both these reasons, trackballs are popular pointing devices for portable computers.
Joystick: A Joystic consists of a lever that moves in all directions and controls the movement of a pointer or some other display symbols. It is similar to a mouse, except that with a mouse the cursor stops moving as soon as you stop moving the mouse. With a joystick, the pointer continues moving in the direction the joystick is pointing. To stop the pointer, you must return the joystick to its upright position. Most joysticks include two buttons called triggers. Joysticks are used mostly for computer games, but they are also used occasionally for CAD/CAM systems and other applications.
Digitizing Tablet: This is an input device that enables you to enter drawings and sketches into a computer. A digitizing tablet consists of an electronic tablet and a cursor or pen. A cursor (also called a puck) is similar to a mouse, except that it has a window with cross hairs for pinpoint placement, and it can have as many as 16 buttons.
A pen (also called a stylus), looks like a simple ballpoint pen but uses an electronic head instead of ink. The tablet contains electronic
signals that enable it to (i) detect movements of the cursor or pen, and (ii) translate the movements into digital signals that it sends to the computer.
For digitizing tablet, each point on the tablet represents a point on the display screen in a fixed manner. Thus it differs from mouse, in which all movement is relative to the current cursor position. The static nature of digitizing tablets makes them particularly effective for tracing drawings. Most modern digitizing tablets also support a 'mouse emulation mode', in which the pen or cursor acts like a mouse.
Digitizing tablets are also called digitizers, graphics tablets, touch tablets, or simply tablets.
Light Pen: Light pen is an input device that utilizes a light sensitive detector to select objects on a display screen. A light pen is similar to a mouse, except that with a light pen you can move the pointer and select objects on the display screen by directly pointing to the objects with the pen.
. Scanner: The keyboard can input only text through keys provided in it. If we want to input a picture, the keyboard cannot help us. Scanner is an optical device that can input any graphical chart or picture and display it back. The common optical scanning devices are Magnetic Ink Character Recognition (MICR), Optical Mark Reader (OMR) and Optical Character Reader (OCR).
Magnetic Ink Character Recognition (MICR): This is widely used by banks to process large volumes of cheques and drafts.
The cheque numbers and other related information is printed with specialized magnetic ink. As the cheques enter the reading unit, the cheques pass through the magnetic field which causes the 'read head' to recognize the cheque number and branch data.
Optical Mark Reader (OMR): This technique is used when students have appeared in objective type tests and they had to mark their answer by darkening a square or circular space by pencil. These answers are directly read and made available to a computer for grading.
Optical Character Recognition (OCR): This technique allows the direct reading of any printed or typed character. Suppose you have a set of hand written or typed text on a piece of paper, the same can be read by the computer. This pattern is compared with a site of patterns stored inside the computer. Whichever pattern is matched is called a character read. Patterns that cannot be identified are rejected.