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The width of an address bus, along with the size of addressable memory elements, determines how much memory can be accessed. For example, a 16-bit wide address bus (commonly used in the 8-bit processors of the 1970s and early 1980s) reaches across 216 = 65,536 = 64 Ki memory locations, whereas a 32-bit address bus (common in Today's PC processors) can address 232 = 4,294,967,296 = 4 Gi locations.

In most Microcomputer s the addressable elements are 8-bit '' Byte s'' (so a "Ki" in that case is equal to a "KiB", i.e. a Kibibyte ), while there are also many examples of computers with larger "chunks" of data as their minimum physically addressable elements, notably some Mainframe s and some Microprocessor s.


Binary prefix Nomenclature

For many years, computer users and manufacturers used the SI prefixes for powers of 103 (kilo-,mega-,giga-) to refer instead to powers of 210. The IEC has now standardized on a Binary Prefix nomenclature to resolve this ambiguity, but the older usage is still common as of 2006.


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