input devices

Input Devices.
Disk units, tape units, and drum units are all input and output (I/O) devices, and they share a common use for mass storage. In this section, we look at a few devices that are used exclusively for input of data. We start with one of the most prevalent devices – the keyboard.
1- Keyboard:
By far the most common input device is the keyboard. It is standard equipment on virtually every personal computer. the essential elements of a keyboard are a switch matrix and a keyboard interface encoder chip. The keyboard encoder is a microprocessor with an in-built ROM. The switch matrix consists of a number of horizontal and vertical lines crossing each other. At each crossing, a small switch operated by a spring –loaded key is located. When a key is pressed, the switch closes and relevant horizontal and vertical lines are shorted. This is then detected by the keyboard encoder, which generates a special 8-bit code known as the scan code. Each key is allocated its own unique scan code. The scan code is entered into internal buffer for transmission to the computer via especial serial cable on the computer side, a keyboard controller. Also known as the keyboard bios chip receives the serial data stream and converts it into an appropriate ASCII code. The keyboard controller is another dedicated processor with an in-built few kilobytes of ROM and hundred bytes Of RAM. The characters you type are stored until the CPU is ready to accept them.
2-Mouse:
since the keyboard is likely to remain the dominate device for entering text. But many operations on personal computers involve pointing selecting or removing items already on the screen, often you can perform these tasks more quickly with pointing devices, such as the touch screen and the mouse.