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{{Short description|Multiple of the unit byte}}{{Distinguish|kilobit}}{{redirect|KByte|the battery electric car from Future Mobility Corporation|Byton K-Byte}}{{Quantities of bytes}}The kilobyte is a multiple of the unit byte for digital information.The International System of Units (SI) defines the prefix kilo as a multiplication factor of 1000 (103); therefore, one kilobyte is 1000 bytes.International Standard IEC 80000-13 Quantities and Units – Part 13: Information science and technology, International Electrotechnical Commission (2008). The internationally recommended unit symbol for the kilobyte is kB.In some areas of information technology, particularly in reference to random-access memory capacity, kilobyte instead typically refers to 1024 (210) bytes. This arises from the prevalence of sizes that are powers of two in modern digital memory architectures, coupled with the coincidence that 210 differs from 103 by less than 2.5%. A kibibyte is 1024 bytes.{{TOC limit|3}}

Definitions and usage

Decimal (1000 bytes)

In the International System of Units (SI) the metric prefix kilo means 1000 (103); therefore, one kilobyte is 1000 bytes. The unit symbol is kB.This is the definition recommended by the International Electrotechnical Commission (IEC).Prefixes for Binary Multiples {{webarchive|url=https://web.archive.org/web/20070808000831weblink |date=2007-08-08 }} — The NIST Reference on Constants, Units, and Uncertainty This definition, and the related definitions of the prefixes mega ({{gaps|1|000|000}}), giga ({{gaps|1|000|000|000}}), etc., are most commonly used for data transfer rates in computer networks, internal bus, hard drive and flash media transfer speeds, and for the capacities of most storage media, particularly hard disk drives,1977 Disk/Trend Report Rigid Disk Drives, published June 1977 flash-based storage,SanDisk USB Flash Drive {{webarchive|url=https://web.archive.org/web/20080513155718weblink |date=2008-05-13 }} "Note: 1 megabyte (MB) = 1 million bytes; 1 gigabyte (GB) = 1 billion bytes." and DVDs. It is also consistent with the other uses of the metric prefixes in computing, such as CPU clock speeds or measures of performance.The international standard IEC 80000-13 uses the term "byte" to mean eight bits (1 B = 8 bit). Therefore, 1 kB = 8000 bit. One thousand kilobytes (1000 kB) is equal to one megabyte (1 MB), where 1 MB is one million bytes.

Binary (1024 bytes)

The term 'kilobyte' has traditionally been used to refer to 1024 bytes (210 B).Kilobyte – Definition and More from the Free Merriam-Webster Dictionary {{webarchive|url=https://web.archive.org/web/20100409171320weblink |date=2010-04-09 }}. Merriam-webster.com (2010-08-13). Retrieved on 2011-01-07.Kilobyte | Define Kilobyte at Dictionary.com {{webarchive|url=https://web.archive.org/web/20100901202451weblink |date=2010-09-01 }}. Dictionary.reference.com (1995-09-29). Retrieved on 2011-01-07.Definition of kilobyte from Oxford Dictionaries Online {{webarchive|url=https://web.archive.org/web/20060625132017weblink |date=2006-06-25 }}. Askoxford.com. Retrieved on 2011-01-07. The usage of the metric prefix kilo for binary multiples arose as a convenience, because 1024 is approximately 1000.WEB, Prefixes for binary multiples,weblink iec.ch, International Electrotechnical Commission, 1 October 2016, live,weblink" title="web.archive.org/web/20160925125914weblink">weblink 25 September 2016, The binary interpretation of metric prefixes is still prominently used by the Microsoft Windows operating system.WEB,weblink Determining Actual Disk Size: Why 1.44 MB Should Be 1.40 MB, Support.microsoft.com, 2003-05-06, 2014-03-25, live,weblink" title="web.archive.org/web/20140209012305weblink">weblink 2014-02-09, Binary interpretation is also used for random-access memory capacity, such as main memory and CPU cache size, due to the prevalent binary addressing of memory.The binary meaning of the kilobyte for 1024 bytes typically uses the symbol KB, with an uppercase letter K. The B 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, the IEC addressed such multiple usages and definitions by creating prefixes such as kibi, mebi, gibi, etc., to unambiguously denote powers of 1024.WEB,weblink Prefixes for binary multiples, National Institute of Standards and Technology, National Institute of Standards and Technology, live,weblink" title="web.archive.org/web/20070808000831weblink">weblink 2007-08-08, "In December 1998 the International Electrotechnical Commission (IEC) [...] approved as an IEC International Standard names and symbols for prefixes for binary multiples for use in the fields of data processing and data transmission." 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. The International System of Units restricts the use of the SI prefixes strictly to powers of 10.{{SIbrochure9th|page=143}}. "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 [...]"

Use of term

• The Shugart SA-400 5{{1/4}}-inch floppy disk (1976) held 109,375 bytes unformatted,WEB,weblink SA400 minifloppy, Swtpc.com, 2013-08-14, 2014-03-25, dead,weblink" title="web.archive.org/web/20140527094602weblink">weblink 2014-05-27, and was advertised as "110 Kbyte", using the 1000 convention.WEB,weblink Archived copy, 2011-06-24, dead,weblink" title="web.archive.org/web/20110608195322weblink">weblink 2011-06-08, Likewise, the 8-inch DEC RX01 floppy (1975) held 256,256 bytes formatted, and was advertised as "256k".WEB,weblink Archived copy, 2011-06-24, dead,weblink" title="web.archive.org/web/20110423194129weblink">weblink 2011-04-23, On the other hand, the Tandon 5{{1/4}}-inch DD floppy format (1978) held 368,640 (which is 360×1024) bytes, but was advertised as "360 KB", following the 1024 convention.
• Early home computer systems would often advertise using the 1024 convention, hence the naming of the Commodore 64, Commodore 128, and the Amstrad CPC 464.
• On modern systems, all versions of Microsoft Windows including the newest ({{as of|2019|lc=y}}) Windows 10 divide by 1024 and represent a 65,536-byte file as "64 KB". Conversely, Mac OS X Snow Leopard and newer represent this as 66 kB, rounding to the nearest 1000 bytes.WEB,weblink How OS X and iOS report storage capacity, Support.apple.com, 2013-07-01, 2014-03-25, live,weblink" title="web.archive.org/web/20140304015219weblink">weblink 2014-03-04, File sizes are reported with decimal prefixes.WEB,weblink How Mac OS X reports drive capacity, Apple Inc, 2009-08-27, 2009-10-16, live,weblink" title="web.archive.org/web/20091222235620weblink">weblink 2009-12-22,
• {{As of|2016|post=,}} the binary interpretation was still used in marketing and billing by some telecommunication companies, such as Vodafone,WEB, Vodafone Ireland, 3G/GPRS data rates,weblink 26 October 2016, live,weblink 26 October 2016, AT&T,WEB, AT&T, Data Measurement Scale,weblink 26 October 2016, {{dead link|date=December 2017 |bot=InternetArchiveBot |fix-attempted=yes }} OrangeWEB, Orange Romania, Internet Mobile Access,weblink 26 October 2016, dead,weblink 26 October 2016, and Telstra.WEB, Telstra, Our Customer Terms, 7,weblink 26 October 2016, live,weblink 10 April 2017,

Data examples

• The Lord's Prayer, in Latin, is 296 bytes.WEB, Vulgata Clementina,weblink 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,
• The short story The Cask of Amontillado by Edgar Allan Poe, hosted on Project Gutenberg as an uncompressed plain text file, is 12,843 bytes: this is 12.8 kilobytes (divided by 1,000) or 12.5 kibibytes (divided by 1,024).WEB,weblink The Cask of Amontillado, Edgar Allan, Poe, Project Gutenberg,

• The novel The Picture of Dorian Gray, by Oscar Wilde, hosted on Project Gutenberg as an uncompressed plain text file, is 428,952 bytes; this is 428.95 kilobytes (divided by 1,000) and 418.90 kibibytes (divided by 1,024). Great Expectations is 994,639 bytes,WEB,weblink Great Expectations, Charles, Dickens, July 1, 1998, Project Gutenberg, and Moby Dick is 1,191,763 bytes.WEB,weblink Moby Dick; Or, The Whale, Herman, Melville, July 1, 2001, Project Gutenberg,

See also

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• History of the floppy disk
• Binary prefix
• Timeline of binary prefixes
• {{Section link|Gigabyte|Consumer confusion}}
• {{Section link|JEDEC memory standards|Unit prefixes for semiconductor storage capacity}}
• {{Section link|Units of information|Size examples}}

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References

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• WEB,weblink Terms, Definitions, and Letter Symbols for Microcomputers, Microprocessors, and Memory Integrated Circuits, December 2002, JEDEC Solid State Technology Association, 22 September 2013,

{{Computer Storage Volumes}}