SECTION III-3: Data Bus and Address Bus in Computers

The address bus is used to identify the devices and memory connected to the CPU, the more address buses available, the larger the number of devices that can be addressed. The number of address buses for a CPU determines the number of locations with which it can communicate. The number of locations is always equal to 2x, where x is the number of address lines, regardless of the size of the data bus. A CPU with 16 address lines can provide a total of 65,536 (216) or 64K of addressable memory. Each location can have a maximum if 1 byte of data. This is because all general-purpose microprocessor CPU's are what is called byte addressable. The IBM PC AT uses a CPU are what is called byte addressable. The total accessible memory is 16 megabytes,  224 = 16 megabytes. There would be 224 locations, as each location is 1 byte, there would be 16 megabytes of memory. The address bus is a unidirectional bus, which means that the CPU uses the address bus only to send out addresses. To summarize, the total number of memory locations addressable by a given CPU is always equal to 2x, where x is the number of address bits, regardless of the size of the data bus.

Data Bus, Address Bus and Control Bus Inside Internal Organization of Computers
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