Input+and+Output+Controller

=**__Input and Output Controller__**=

The processor communicates through mechanisms and devices that are grouped into I/O (input and output) controllers and I/O devices.

I/O controllers include the keyboard controller and magnetic disk controller. Peripheral devices cannot be connected directly to the CPU. If processors controlled peripherals directly, the invention of a new type of peripheral would require the processor to be redesigned.

Some I/O controllers can both input and output bits, such as a floppy disk controller. Most other controllers operate in one direction only. For example, a keyboard is only an input controller and a VDU (visual display unit) is only an output controller.

The controller consists of three different parts:
 * Electronics that interface the controller to the bus.
 * A set of data, command and status registers.
 * Electronics appropriate for sending control signals to the device connected to the computer.