Field Guide · concept

A system bus is the shared set of electrical conductors that moves data, addresses, and control signals between a computer’s CPU, memory, and I/O devices.1

CPU address bus data bus control bus RAM I/O devices where a value goes · what the value is · when to move it
A classic system bus is really three buses working together: the address bus names a location, the data bus carries the value, and the control bus says read or write and when. CPU, RAM, and I/O all hang off the same shared lines — which is why heavy traffic makes the bus a bottleneck, and why modern machines split it into point-to-point links.

Overview

Classically a bus has three parts: a data bus (the values being moved), an address bus (which memory location or device they go to), and a control bus (timing and read/write signals). The bus width — how many bits cross at once — and its clock set the bandwidth. This shared design comes straight from the von Neumann architecture, where one path connects the processor to a common memory and devices.

Where it fits

Because the components on the motherboard cannot talk directly, the bus is the meeting point, and a shared bus can become a bottleneck when many devices compete for it. Modern systems mostly replace one wide shared bus with many fast point-to-point links — PCIe being the dominant example — but the concept is unchanged: a defined interconnect that lets the parts of a computer exchange data in step.

Sources

  1. Bus (computing) — Wikipedia, on data, address, and control buses. ↩

See also