Address bus
Address buses are made up of a collection of wires connecting the CPU with main memory that is used to identify particular locations (addresses) in main memory. The width of the address bus (that is, the number of wires) determines how many unique memory locations can be addressed. Modern personal computers and Macintoshes have as many as 36 address lines. This theoretically allows them to access 64 gigabytes of main memory. However, the actual amount of memory that can be accessed is usually much less than this theoretical limit due to chipset and motherboard limitations.