Input, output, and secondary storage devices are connected to computer through expansion boards with circuitries that control the devices operation. These boards are inserted into motherboard slots. Examples of these boards are video adapters, fax/modem boards, sound boards, and disk controllers. Some boards have exterior sockets (ports) through which external devices can be connected. Port types include:

- Serial ports that transmit a single bit at a time. They require inexpensive cables and they reliable deliver data over long distances. Mice and other devices may be connected to computer through serial ports.

- Parallel ports that transmit eight bits (one byte) at a time. Printers and scanners may be connected to computer through parallel ports.

- Monitor, mouse, keyboard, modem, network, speaker, and microphone ports

- USB ports with each being capable of supporting up to 127 peripheral devices, so you are never out of ports. USB ports greatly simplify connecting devices to computer. Most peripherals now come in USB versions. Several peripherals can be connected through a single USB port by chaining them together or by using USB hubs.