Interface

An I/O interface is required whenever the I/O device is driven by the processor. Typically a CPU communicates with devices via a bus.

The interface must have necessary logic to interpret the device address generated by the processor. Handshaking should be implemented by the interface using appropriate commands (like BUSY, READY, and WAIT), and the processor can communicate with an I/O device through the interface. If different data formats are being exchanged, the interface must be able to convert serial data to parallel form and vice versa. Because it would be a waste for a processor to be idle while it waits for data from an input device there must be provision for generating interrupts and the corresponding type numbers for further processing by the processor if required.

A computer that uses memory-mapped I/Oaccesses hardware by reading and writing to specific memory locations, using the same assembly language instructions that computer would normally use to access memory. An alternative method is via instruction-based I/O which requires that a CPU have specialised instructions for I/O.Both input and output devices have a data processing  rate that can vary greatly.^[2] With some devices able to exchange data at very high speeds direct access  to memory (DMA) without the continuous aid of a CPU is required.