The address determines the destination or source of information. Since the wires of a bus are common to all functional units, each unit will see all the data placed on the bus lines. The address lines are used within a receiving unit to determine if available information should be processed or ignored. Each data repository on a common bus will have a unique address.
When the CPU needs to transfer data between itself and a particular location, it implements a sequence of signals as specified by the read or write operation protocol for the bus. The range of numbers that can be represented by the available address lines (wires) on a bus is known as the address space. A range of numbers is used mostly to access information from memory and is thus known as the memory address space. Some processors assign a few of these memory addresses to other input/output devices. A feature known as memory-mapped I/O.