Editing Binary prefix (section)

{{Short description|Symbol placed before units of digital information to indicate multiplication by a power of two}}
{{About|powers-of-two prefixes for measurement units like bit and byte|notations for the radix of a numeral|Integer literal#Affixes}}
{{Use dmy dates|date=May 2019|cs1-dates=y}}
{{Redirect|Gibi|other uses|Gibi (disambiguation)}}

{{Bit and byte prefixes}}

A '''binary prefix''' is a [[unit prefix]] that indicates a [[multiple (mathematics)|multiple]] of a [[units of measurement|unit of measurement]] by an integer [[powers of two|power of two]]. The most commonly used binary prefixes are '''kibi''' (symbol Ki, meaning {{nowrap|1=2<sup>10</sup> = 1024}}), '''mebi''' ({{nowrap|1=Mi, 2<sup>20</sup> = {{val|1048576}}}}), and '''gibi''' ({{nowrap|1=Gi, 2<sup>30</sup> = {{val|1073741824}}}}). They are most often used in [[information technology]] as multipliers of [[bit]] and [[byte]], when expressing the capacity of [[Data storage device|storage device]]s or the size of computer [[file (computer)|files]].

The binary prefixes "kibi", "mebi", etc. were defined in 1999 by the [[International Electrotechnical Commission]] (IEC), in the [[IEC 60027-2]] [[Technical standard|standard]] (Amendment 2). They were meant to replace the [[International System of Units|metric (SI)]] [[power of 10|decimal power]] prefixes, such as "kilo" ({{nowrap|1=k, 10<sup>3</sup> = 1000}}), "mega" ({{nowrap|1=M, 10<sup>6</sup> = {{val|1000000}}}}) and "giga" ({{nowrap|1=G, 10<sup>9</sup> = {{val|1000000000}}}}),<ref name="BIPM8" /> that were commonly used in the computer industry to indicate the nearest powers of two. For example, a memory module whose capacity was specified by the manufacturer as "2&nbsp;megabytes" or "2&nbsp;MB" would hold {{nowrap|2 × 2<sup>20</sup>}} = {{nowrap|{{val|2097152}} bytes}}, instead of {{nowrap|2 × 10<sup>6</sup>}} = {{val|2000000}}.

On the other hand, a hard disk whose capacity is specified by the manufacturer as "10 gigabytes" or "10&nbsp;GB", holds {{nowrap|10 × 10<sup>9</sup>}} = {{val|10000000000}} bytes, or a little more than that, but less than {{nowrap|10 × 2<sup>30</sup>}} = {{val|10737418240}} and a file whose size is listed as "2.3&nbsp;GB" may have a size closer to {{nowrap|2.3 × 2<sup>30</sup>}} ≈ {{val|2470000000}} or to {{nowrap|2.3 × 10<sup>9</sup>}} = {{val|2300000000}}, depending on the [[program (computer)|program]] or [[operating system]] providing that measurement. This kind of ambiguity is often confusing to computer system users and has resulted in [[lawsuit]]s.<ref name="suitxxxx" /><ref name="sand2021" /> The IEC 60027-2 binary prefixes have been incorporated in the [[ISO/IEC 80000#Part 13: Information science and technology|ISO/IEC 80000]] standard and are supported by other standards bodies, including the [[International Bureau of Weights and Measures|BIPM]], which defines the SI system,<ref name="BIPM8" />{{rp|p.121}} the [[United States|US]] [[National Institute of Standards and Technology|NIST]],<ref name="NIST1" /><ref name="NIST2" /> and the [[European Union]].

Prior to the 1999 IEC standard, some industry organizations, such as the [[JEDEC memory standards#Unit prefixes for semiconductor storage capacity|Joint Electron Device Engineering Council]] (JEDEC), noted the common use of the terms ''kilobyte'', ''megabyte'', and ''gigabyte'', and the corresponding symbols ''KB'', ''MB'', and ''GB'' in the binary sense, for use in storage capacity measurements. However, other computer industry sectors (such as [[magnetic storage]]) continued using those same terms and symbols with the decimal meaning. Since then, the major standards organizations have expressly disapproved the use of SI prefixes to denote binary multiples, and recommended or mandated the use of the IEC prefixes for that purpose, but the use of SI prefixes in this sense has persisted in some fields.