Address bus

An address bus is a computer bus architecture. It is used to transfer data between devices. The devices are identified by the hardware address of the physical memory (the physical address). The address is stored in the form of binary numbers to enable the data bus to access memory storage. 
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. 
An address bus is part of the system bus architecture, which was developed to decrease costs and enhance modular integration. However, most modern computers use a variety of individual buses for specific tasks. 
An individual computer contains a system bus, which connects the major components of a computer system and has three main elements, of which the address bus is one, along with the data bus and control bus.
An address bus is measured by the amount of memory a system can retrieve. A system with a 32-bit address bus can address 4 gigabytes of memory space. Newer computers using a 64-bit address bus with a supporting operating system can address 16 exbibytes of memory locations, which is virtually unlimited.