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binary prefix
A binary prefix is a prefix attached before a unit symbol to multiply it by a power of 2. In computing, such a prefix is seen in combination with a unit of information (bit, byte, etc.), to indicate a power of 1024.
The computer industry has historically used the units ''kilobyte'', ''megabyte'', and ''gigabyte'', and the corresponding symbols KB, MB, and GB, in at least two slightly different measurement systems. In citations of main memory (RAM) capacity, ''gigabyte'' customarily means bytes. As this is the third power of 1024, and 1024 is a power of two (210), this usage is referred to as a binary prefix.
In most other contexts, the industry uses the multipliers ''kilo'', ''mega'', ''giga'', etc., in a manner consistent with their meaning in the International System of Units (SI), namely as powers of 1000. For example, a 500 gigabyte hard disk holds bytes, and a 100-megabit-per-second Ethernet connection transfers data at bit/s. In contrast with the ''binary prefix'' usage, this use is described as a ''decimal prefix'', as 1000 is a power of 10 (103).
The use of the same unit prefixes with two different meanings has caused confusion. Starting around 1998, the International Electrotechnical Commission (IEC) and several other standards and trade organizations addressed the ambiguity by publishing standards and recommendations for a set of binary prefixes that refer exclusively to powers of 1024. Accordingly, the US National Institute of Standards and Technology (NIST) requires that SI prefixes only be used in the decimal sense: kilobyte and megabyte denote one thousand bytes and one million bytes respectively (consistent with SI), while new terms such as kibibyte, mebibyte and gibibyte, having the symbols KiB, MiB, and GiB, denote 1024 bytes, bytes, and bytes, respectively.〔 In 2008, the IEC prefixes were incorporated into the IEC 80000-13 standard.
==History==
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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