A bus is a communication pathway that transfers data, addresses, and control signals between components inside a computer or between a computer and its devices. Examples include the memory bus, PCIe, SATA, and USB.
Why it matters
A bus's performance is set by its width (how many bits move at once), its clock or transfer rate, and how many devices share it. Narrow or slow buses become bottlenecks, even when the components on either end are fast. Older designs used one shared parallel bus, while modern systems mostly use point-to-point serial links, which reach higher speeds with fewer wires.
Historically, buses were described as three groups of lines: the data bus carries the values, the address bus selects the location, and the control bus carries read, write, and timing signals.
Example
A memory channel is 64 bits (8 bytes) wide. At 3200 million transfers per second, its peak bandwidth is 8 x 3200 = 25,600 MB/s, or 25.6 GB/s. If the CPU can consume data faster than that, the bus becomes the limit.
Common mistakes
- Using "bus" to mean a single fixed standard. It is a general concept.
- Looking only at device speed and ignoring the link it connects through.
- Plugging a fast NVMe drive into a slot wired for fewer PCIe lanes than expected.
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