An address bus is (part of) a computer bus, used by CPUss or DMA-capable units for communicating the physical addresses of computer memory elements/locations that the requesting unit (CPU/DMA) wants to access.

The width of an address bus determines how much memory can be accessed. For example, a 16-bit address bus reaches across 216 = 65,536 = 64K memory locations, while a 32-bit bus can address 4,294,967,296 = 4G locations.