Chapter 1
INPUT/OUTPUT DEVICES
1.1 INPUT DEVICES
1.1.1 Keyboard
Keyboard is an input device; consisting of a set of typewriter-like keys that enables to enter data into a
computer.
Figure 1. 1
The keys on computer keyboards are often classified as follows:
1.1.1.1 Alphanumeric Keys – letters and numbers
1.1.1.2 Punctuation Keys – comma, period, semicolon, and so on.
1.1.1.3 Special Keys – function keys, control keys, arrow keys, Caps Lock key, and so on.
1.1.2 Mouse
Mouse is a device that controls the movement of the cursor or pointer on a display screen. It is a small
object that can roll along a hard flat surface.
Figure 1. 2
There are three basic types of mouse:
1.1.2.1 Mechanical – It has a rubber or metal ball on its underside that can roll in all directions. Mechanical
sensors within the mouse detect the direction in which the ball is rolling and move the screen pointer
accordingly.
1.1.2.2 Optomechanical – It is same as a mechanical mouse, but uses optical sensors to detect motion of
the ball.
1.1.2.3 Optical – It has a laser to detect the mouse’s movement. One must move the mouse along a special
mat with a grid so that the optical mechanism has a frame of reference. Optical mice have no mechanical
moving parts.
1.1.3 Trackball
It is another pointing device. Essentially, a trackball is a mouse lying on its back. To move the pointer, we
rotate the ball with our thumb, our fingers, or the palm of our hand.
1.1.4 Joystick
With a joystick, the pointer continues moving in the direction the joystick is moving. To stop the pointer, we
must return the joystick to its upright position
1.2 OUTPUT DEVICES
An output device is any machine capable of representing information from a computer. Output devices
include display screens, loudspeakers, printers, plotters, etc.
1.2.1 Monitor
Monitor is another term for the display screen. The term monitor usually refers to the entire box, whereas
display screen can mean just the screen.
Figure 1. 3
1.2.1.1 Digital Monitor – A digital monitor accepts digital signals rather than analog signals. It translates the
digital signals into analog signals that control the actual display.
1.2.1.2 Analog Monitor – This is the traditional type of color display screen that has been used for years in
televisions.
1.2.2 Printer
Printer is a device that prints text or illustrations on paper.
Figure 1. 4
There are many difference types of printers:
1.2.2.1 Daisy-wheel Printer – A daisy-wheel printer is a type of printer that produces letter-quality type. The
daisy wheel is a disk made of plastic or metal on which characters stand out in relief along the outer edge.
To print a character, the printer rotates the disk until the desired letter is facing the paper. Then a hammer
strikes the disk, forcing the character to hit an ink ribbon, leaving an impression of the character on the
paper.
1.2.2.2 Dot-matrix Printer – Dot-matrix printers create characters by striking pins against an ink ribbon. Each
pin makes a dot, and combinations of dots form characters and illustrations.
1.2.2.3 Ink-jet Printer – Ink-jet printers work by spraying ionized ink at a sheet of paper. Magnetized plates in
the ink’s path direct the ink onto the paper in the desired shapes.
1.2.2.4 Laser Printer – Laser printer utilizes a laser beam to produce an image on a drum. The light of the
laser alters the electrical charge on the drum wherever it hits. The drum is then rolled through a reservoir of
toner, which is picked up by the charged portions of the drum. Finally, the toner is transferred to the paper
through a combination of heat and pressure.
1.2.3 Plotter
Plotter is a device that draws pictures on paper based on commands from a computer.
Figure 1. 5
1.2.4 Sound Cards and Speakers
Sound card is an expansion board that enables a computer to manipulate and output sounds. Sound cards
enable the computer to output sound through speakers connected to the board, to record sound input from a
microphone connected to the computer, and manipulate sound stored on a disk.
1.2.5 3D-Audio
3D audio is a technique for giving more depth to traditional stereo sound. Typically, 3D audio is produced by
placing a device in a room with stereo speakers. The device dynamically analyzes the sound coming from
the speakers and sends feedback to the sound system so that it can readjust the sound to give the
impression that the speakers are further apart.
Figure 1. 6
