I/O is the abbreviation of input/output, which is the input and output port. Each device has a dedicated I/O address that handles its own input and output information.

The connection of the CPU to external devices, memory, and data exchange are all required to be implemented by an interface device, the former being referred to as an I/O interface and the latter being referred to as a memory interface.

The memory usually works under the synchronous control of the CPU, and the interface circuit is relatively simple; and the I/O devices are various in variety, and the corresponding interface circuits are also different. Therefore, it is customary to say that the interface refers only to the I/O interface.