How a Computer Works (2015)
9. PCI Bus
The motherboard is a large PCB fitted into the main system box. All peripherals and devices ultimately connect to the motherboard.
The motherboard contains chips for processing instructions. Connectors on the motherboard allow peripherals and devices to connect.
Motherboards in a PC use the PCI bus specification. A system bus on a motherboard is like a 32 lane motorway where data moves between chips. The PCI bus specification exists to maintain a specification that all motherboard manufacturers can follow. This enables compatibility between computer PCs and peripherals.
Although components used on motherboards differ the specification remains consistent.
Expansion cards plug into the PCI connector. The expansion card needs to meet the PCI standard.