I/O devices are manipulated via a set of registers referred to as "i/o interface ports" or sometimes as "i/o registers." These are not to be confused with cpu registers. They are not in the cpu, but rather the i/o device is connected to the bus through i/o interface ports.

Example:

A printer connected to a pc might have three ports:

1. printer data port
2. printer status port
3. printer control port