TheInternational System of Units (SI) defines the prefixkilo as a multiplication factor of 1000 (103); therefore, one kilobyte is 1000 bytes.[1] The internationally recommended unit symbol for the kilobyte iskB.[1]
In some areas ofinformation technology, particularly in reference torandom-access memory capacity,kilobyte instead often refers to 1024 (210) bytes. This arises from the prevalence of sizes that arepowers of two in modern digital memory architectures, coupled with the coincidence that 210 differs from 103 by less than 2.5%.
Thekibibyte is defined as 1024 bytes, avoiding the ambiguity issues of thekilobyte.[1]
The international standardIEC 80000-13 uses the term "byte" to mean eightbits (1 B = 8 bit). Therefore, 1 kB = 8000 bit. One thousand kilobytes (1000 kB) is equal to onemegabyte (1 MB), where 1 MB is one million bytes.
The term 'kilobyte' has traditionally been used to refer to 1024 bytes (210 B).[5][6][7] The usage of the metric prefixkilo for binary multiples arose as a convenience, because 1024 is approximately 1000.[8]
The binary interpretation of metric prefixes is still prominently used by theMicrosoft Windows operating system.[9] Binary interpretation is also used forrandom-access memory capacity, such as main memory andCPU cache size, due to the prevalentbinary addressing of memory.
The binary meaning of the kilobyte for 1024 bytes typically uses the symbol KB, with an uppercase letterK. TheB is sometimes omitted in informal use. For example, a processor with 65,536 bytes of cache memory might be said to have "64 K" of cache. In this convention, one thousand and twenty-four kilobytes (1024 KB) is equal to one megabyte (1 MB), where 1 MB is 10242 bytes.
In December 1998, theIEC addressed such multiple usages and definitions by creating prefixes such as kibi, mebi, gibi, etc., to unambiguously denote powers of 1024.[10] Thus the kibibyte, symbol KiB, represents 210 bytes = 1024 bytes. These prefixes are now part of IEC 80000-13. The IEC further specified that the kilobyte should only be used to refer to 1000 bytes. TheInternational System of Units restricts the use of the SI prefixes strictly to powers of 10.[11]
TheShugart SA-400 51⁄4-inchfloppy disk (1976) held 109,375 bytes unformatted,[12] and was advertised as "110 Kbyte", using the 1000 convention.[13] Likewise, the 8-inchDEC RX01 floppy (1975) held 256,256 bytes formatted, and was advertised as "256k".[14] On the other hand, theTandon 51⁄4-inchDD floppy format (1978) held 368,640 (which is 360×1024) bytes, but was advertised as "360 KB", following the 1024 convention.
On modern systems, all versions ofMicrosoft Windows divide by 1024 and represent a 65,536-byte file as "64 KB".[9] Conversely,Mac OS X Snow Leopard and newer represent this as 66 kB, rounding to the nearest 1000 bytes;[15] file sizes are reported with decimal prefixes.[16]
^abcInternational StandardIEC 80000-13 Quantities and Units – Part 13: Information science and technology, International Electrotechnical Commission (2008).
^The International System of Units(PDF) (9th ed.), International Bureau of Weights and Measures, Dec 2022, p. 143,ISBN978-92-822-2272-0. "The SI prefixes refer strictly to powers of 10. They should not be used to indicate powers of 2 (for example, one kilobit represents 1000 bits and not 1024 bits). The names and symbols for prefixes to be used with powers of 2 are recommended as follows: kibi Ki 210 [...]"
^"Our Customer Terms"(PDF). Telstra. p. 7.Archived(PDF) from the original on 10 April 2017. Retrieved26 October 2016.
^"Vulgata Clementina".Archived from the original on 2022-12-05. Retrieved2024-02-29.pater noster qui es in cælis sanctificetur nomen tuum adveniat regnum tuum fiat voluntas tua sicut in cælo et in terra panem nostrum supersubstantialem da nobis hodie et dimitte nobis debita nostra sicut et nos dimittimus debitoribus nostris et ne nos inducas in tentationem sed libera nos a malo
^Dickens, Charles (July 1, 1998).Great Expectations.Archived from the original on February 29, 2024. RetrievedFebruary 29, 2024 – via Project Gutenberg.
^Melville, Herman (July 1, 2001).Moby Dick; Or, The Whale.Archived from the original on February 29, 2024. RetrievedFebruary 29, 2024 – via Project Gutenberg.
