An external bus primarily enables connecting peripherals and all external devices to a computer. These devices can include storage, monitors, keyboard, mouse and more.

Typically, an external bus is composed of electrical circuits that connect and transmit data between the computer and the external device. Being external to the computer, external buses are much slower than internal buses. Moreover, an external bus can be both serial or parallel.

Universal Serial Bus (USB) , PCI bus and IEEE 1294 are common examples of external buses.