I/O devices connect the computer to the outside world. In our example, we have four I/O devices: a keyboard and mouse for input, a display for output, and a disk drive for long-term storage. Each I/O device connects to the system via the I/O bus through a controller (built into the device or motherboard) or an adapter (a card that plugs into the motherboard). Both serve to transfer data between the I/O bus and the I/O devices.