The size or width of a bus is how many bits it carries in parallel. Common bus sizes are: 4 bits, 8 bits, 12 bits, 16 bits, 24 bits, 32 bits, 64 bits, 80 bits, 96 bits, and 128 bits. Such buses are in wide use, to link:
- CPU and on-board Memory.
- multiple CPUs in a multi-cpu system
- Arithmetic logic unit to the rest of the CPU
- hard drives, graphics cards, etc. to the main system.