(3) Input Devices

Input hardware consists of external devices – i.e. components outside of the computer's CPU – that are used to enter information and instructions into a computer for storage or processing. The purpose of an input device is to convert incoming data into binary code (i.e. combinations of 0s and 1s) understandable to a digital computer. The most common input devices are a keyboard and a mouse.

A keyboard is a device with buttons or keys that a user presses to enter text, commands, numbers, or other data into a computer. The most used English-language keyboard is called QWERTY. (It was created by an American inventor and printer Christopher Sholes in the late 1860s.) QWERTY is not a word. It is the first six letters in the top alphabet row on a keyboard. That combination of letters is often used to name the standard keyboard in contrast to other keyboards. The minimum number of keys on a board is 44 but modern keyboards may have more than 100 buttons.

A mouse is a mechanical or optical hand-held device. It has two/three buttons and a stroll wheel on the top as well as a rolling ball or an optical sensor in its base. To move the cursor on the display screen, the user moves the mouse around on a flat surface. When the cursor reaches the required location, the user presses the right or left button on the mouse once or twice. Clicking the button, the user can select operations, activate commands, create or change images on the screen.

A trackball, joystick, light pen, and laser scanner also refer to input devices.

Atrackball is an inverted mouse. (See Figure 5) The only functional difference between a mechanical mouse and a trackball is in how the ball is moved. With a mouse, the ball is rolled by moving the whole unit over a desktop or other surface. With a trackball, the user rotates the ball itself while the unit is stationary. One of the main advantages of a trackball is that it takes little desktop surface. Figure 5

Trackball

A joystick is a pointing device used primarily for playing computer video games. A joystick usually has a square or rectangular plastic base to which is attached a vertical lever. Control buttons are located on the base and sometimes on top of the lever. The lever can be moved in multiple directions to control the movement of a cursor or other graphical object on the screen.

A light pen (or stylus) is a device like an ordinary pen that can be used to write text or draw an image directly on a special screen or to select information on the screen by pressing the light pen against the surface of the screen. Light pens are often used in computer-aided design and computer-aided manufacture (CAD and CAM) technology.

An optical scanner is used to enter graphics as well as typeset characters. This device reads images such as a picture or text on a printed page and translates them into binary numbers that the CPU can use. For example, a photograph can be scanned into a computer and then included in a text document created on that computer.

A microphone and a voice recognition unit can be also used to feed data into the computer. A microphone is a device converting sound into signals that can then be stored, manipulated, and reproduced by the computer. A voice recognition module is a device that converts spoken words into information that the computer can recognize and process.