An address bus is a crucial component in a computer's architecture that carries the addresses of data between the processor and memory. It allows the CPU to specify where data is stored or retrieved in the system's memory. The width of the address bus, measured in bits, determines how many unique addresses can be accessed, influencing the maximum memory capacity of the system. For example, a 32-bit address bus can access up to 4 gigabytes of memory, while a 64-bit address bus can access significantly more. The address bus works alongside the data bus, which carries the actual data being transferred, and the control bus, which manages the operations of the system.