Computer Input Output

            
             Input device is used to transmit data to the processing and storage hardware. The data to be input can be in source from, a form that human perceive, or in machine form, a form that can be electronically sensed by another computer. Any device that allows information from outside the computer to be communicated to the computer is considered an input device. Since the central processing unit ( CPU ) of a digital computer can understand only discrete binary information, all computer input devices and circuitry must eventually communicate with the computer in this form. Many devices are capable of performing this task. Some common computer graphics input devices are:.
             1) Keyboard.
             2) Trackball.
             3) Joystick.
             4) Mouse.
             5) Paddle controls.
             6) Light Pen.
             7) Magnetic table .
             8) Digitizing camera.
             9) Scanner.
             10) Bar Code Reader.
             11) Modem.
             12) Voice Recognition device.
             Variety of Input devices:.
             .
             Input devices are of two basic types one is analog and another is digital. Humans perceive a continuous universe; digital devices sense a discrete universe consisting of discrete segments. For example, the temperature indicated by a digital thermometer may be observed to change 73 to 74 degrees instantaneously. The device that is capable of recording continuous changes is an analog device; the device which can sense only discrete changes is a digital device.
             Time is also perceived as continuous. Therefore, a digital device must take "snapshots" of the environment with sufficient rapidity if a high degree of accuracy is to be attained. When a computer takes a snapshot of the environment by obtaining a value from an input device, is to be strobe the device.
             Analog to Digital Conversion:.
             In order to send analogue signals over a digital communication system, or process them on a digital computer, we need to convert analogue signals to digital ones. The conversion of continuous analog signals to discrete data is called analog-to-digital conversion, or simply A/D conversion.