View source for Kilobyte

{{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 [[Computer data storage|digital information]].

The [[International System of Units]] (SI) defines the prefix ''[[kilo-|kilo]]'' as a multiplication factor of 1000 (10<sup>3</sup>); therefore, one kilobyte is 1000&nbsp;bytes.<ref name="IEC80000">International Standard [[IEC 80000-13]] Quantities and Units – Part 13: Information science and technology, International Electrotechnical Commission (2008).</ref> The internationally recommended unit symbol for the kilobyte is '''kB'''.<ref name="IEC80000" />

In some areas of [[information technology]], particularly in reference to [[random-access memory]] capacity, ''kilobyte'' instead often refers to 1024 (2<sup>10</sup>) bytes. This arises from the prevalence of sizes that are [[powers of two]] in modern digital memory architectures, coupled with the coincidence that 2<sup>10</sup> differs from 10<sup>3</sup> by less than 2.5%. 

The [[kibibyte]] is defined as 1024&nbsp;bytes, avoiding the ambiguity issues of the ''kilobyte''.<ref name="IEC80000">International Standard [[IEC 80000-13]] Quantities and Units – Part 13: Information science and technology, International Electrotechnical Commission (2008).</ref>
{{TOC limit|3}}

==Definitions and usage==
===Decimal (1000&nbsp;bytes)===
In the [[International System of Units]] (SI) the [[metric prefix]] ''[[kilo-|kilo]]'' means 1,000 (10<sup>3</sup>); therefore, one kilobyte is 1000&nbsp;bytes. The unit symbol is kB.

This is the definition standardised by the [[International Electrotechnical Commission]] (IEC).<ref name="NIST">[http://physics.nist.gov/cuu/Units/binary.html Prefixes for Binary Multiples] {{webarchive|url=https://web.archive.org/web/20070808000831/http://physics.nist.gov/cuu/Units/binary.html |date=2007-08-08 }} — The NIST Reference on Constants, Units, and Uncertainty</ref> This definition, and the related definitions of the prefixes [[mega-|mega]] ({{gaps|1,000,000}}), [[giga-|giga]] ({{gaps|1,000,000,000}}), etc., are most commonly used for [[Data rate|data transfer rate]]s in [[computer network]]s, internal bus, hard drive and flash media transfer speeds, and for the capacities of most [[Data storage|storage media]], particularly [[hard disk drive]]s,<ref>1977 Disk/Trend Report Rigid Disk Drives, published June 1977</ref> [[Flash memory|flash]]-based storage,<ref>[http://apac.sandisk.com/Products/Catalog(1349)-SanDisk_Extreme_Ducati_Edition_USB_Flash_Drive.aspx SanDisk USB Flash Drive] {{webarchive|url=https://web.archive.org/web/20080513155718/http://apac.sandisk.com/Products/Catalog%281349%29-SanDisk_Extreme_Ducati_Edition_USB_Flash_Drive.aspx |date=2008-05-13 }} "Note: 1&nbsp;megabyte (MB) = 1&nbsp;million bytes; 1&nbsp;gigabyte (GB) = 1&nbsp;billion bytes."</ref> and [[DVD]]s. It is also consistent with the other uses of the metric prefixes in computing, such as [[Hertz#Computers|CPU clock speeds]] or [[FLOPS|measures of performance]].

The international standard [[ISO/IEC 80000|IEC 80000-13]] uses the term "byte" to mean eight [[bit]]s (1&nbsp;B = 8&nbsp;bit). Therefore, 1&nbsp;kB = 8000&nbsp;bit. One thousand kilobytes (1000&nbsp;kB) is equal to one [[megabyte]] (1&nbsp;MB), where 1&nbsp;MB is one million bytes.

===Binary (1024&nbsp;bytes)===
The term 'kilobyte' has traditionally been used to refer to 1024&nbsp;bytes (2<sup>10</sup>&nbsp;B).<ref>[http://www.merriam-webster.com/dictionary/kilobyte Kilobyte – Definition and More from the Free Merriam-Webster Dictionary] {{webarchive|url=https://web.archive.org/web/20100409171320/http://www.merriam-webster.com/dictionary/kilobyte |date=2010-04-09 }}. Merriam-webster.com (2010-08-13). Retrieved on 2011-01-07.</ref><ref>[http://dictionary.reference.com/browse/kilobyte Kilobyte | Define Kilobyte at Dictionary.com] {{webarchive|url=https://web.archive.org/web/20100901202451/http://dictionary.reference.com/browse/kilobyte |date=2010-09-01 }}. Dictionary.reference.com (1995-09-29). Retrieved on 2011-01-07.</ref><ref>[http://www.askoxford.com/concise_oed/kilobyte?view=uk Definition of kilobyte from Oxford Dictionaries Online] {{webarchive|url=https://web.archive.org/web/20060625132017/http://www.askoxford.com/concise_oed/kilobyte?view=uk |date=2006-06-25 }}. Askoxford.com. Retrieved on 2011-01-07.</ref> The usage of the metric prefix ''kilo'' for binary multiples arose as a convenience, because 1024 is approximately 1000.<ref>{{cite web|title=Prefixes for binary multiples|url=http://www.iec.ch/si/binary.htm|website=iec.ch|publisher=International Electrotechnical Commission|access-date=1 October 2016|url-status=live|archive-url=https://web.archive.org/web/20160925125914/http://www.iec.ch/si/binary.htm|archive-date=25 September 2016}}</ref>

The binary interpretation of metric prefixes is still prominently used by the [[Microsoft Windows]] operating system.<ref name="auto">{{cite web |url=http://support.microsoft.com/kb/121839 |title=Determining Actual Disk Size: Why 1.44 MB Should Be 1.40 MB |publisher=Support.microsoft.com |date=2003-05-06 |access-date=2014-03-25 |url-status=live |archive-url=https://web.archive.org/web/20140209012305/http://support.microsoft.com/kb/121839 |archive-date=2014-02-09 }}</ref> Binary interpretation is also used for [[random-access memory]] capacity, such as main memory and [[CPU cache]] size, due to the prevalent [[binary address]]ing of memory.

The binary meaning of the kilobyte for 1024&nbsp;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&nbsp;bytes of cache memory might be said to have "64&nbsp;K" of cache. In this convention, one thousand and twenty-four kilobytes (1024&nbsp;KB) is equal to one megabyte (1&nbsp;MB), where 1&nbsp;MB is 1024<sup>2</sup>&nbsp;bytes.

In December 1998, the [[International Electrotechnical Commission|IEC]] addressed such multiple usages and definitions by creating prefixes such as kibi, mebi, gibi, etc., to unambiguously denote powers of 1024.<ref>{{cite web|url=http://physics.nist.gov/cuu/Units/binary.html|title=Prefixes for binary multiples|author=National Institute of Standards and Technology|author-link=National Institute of Standards and Technology|url-status=live|archive-url=https://web.archive.org/web/20070808000831/http://physics.nist.gov/cuu/Units/binary.html|archive-date=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."</ref> Thus the kibibyte, symbol KiB, represents 2<sup>10</sup>&nbsp;bytes = 1024&nbsp;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&nbsp;bytes.  The [[International System of Units]] restricts the use of the SI prefixes strictly to powers of 10.<ref>{{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&nbsp;bits and not 1024&nbsp;bits). The names and symbols for prefixes to be used with powers of 2 are recommended as follows: kibi Ki 2<sup>10</sup> [...]"</ref>

==Use of term==
* The [[Shugart Associates|Shugart]] SA-400 5{{1/4}}-inch [[floppy disk]] (1976) held 109,375&nbsp;bytes unformatted,<ref>{{cite web |url=http://www.swtpc.com/mholley/SA400/SA400_Index.htm |title=SA400 minifloppy |publisher=Swtpc.com |date=2013-08-14 |access-date=2014-03-25 |url-status=dead |archive-url=https://web.archive.org/web/20140527094602/http://www.swtpc.com/mholley/SA400/SA400_Index.htm |archive-date=2014-05-27 }}</ref> and was advertised as "110 Kbyte", using the 1000 convention.<ref>{{cite web |url=http://www.swtpc.com/mholley/SA400/SA400_Datasheet.pdf |title=Shugart Associates SA 400 minifloppy TM Disk Drive |access-date=2011-06-24 |url-status=dead |archive-url=https://web.archive.org/web/20110608195322/http://www.swtpc.com/mholley/SA400/SA400_Datasheet.pdf |archive-date=2011-06-08 }}</ref>  Likewise, the 8-inch [[Digital Equipment Corporation|DEC]] RX01 floppy (1975) held 256,256&nbsp;bytes formatted, and was advertised as "256k".<ref>{{cite web |url=http://bitsavers.org/pdf/dec/disc/rx01/EK-RX01-MM-002_maint_Dec76.pdf |title=RXS/RX11 floppy disk system maintenance manual |access-date=2011-06-24 |url-status=dead |archive-url=https://web.archive.org/web/20110423194129/http://www.bitsavers.org/pdf/dec/disc/rx01/EK-RX01-MM-002_maint_Dec76.pdf |archive-date=2011-04-23 }}</ref>  On the other hand, the [[Tandon Corporation|Tandon]] 5{{1/4}}-inch [[double density|DD]] floppy format (1978) held 368,640 (which is 360×1024) bytes, but was advertised as "360&nbsp;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]] divide by 1024 and represent a 65,536-byte file as "64&nbsp;KB".<ref name="auto"/> Conversely, [[Mac OS X Snow Leopard]] and newer represent this as 66&nbsp;kB, rounding to the nearest 1000&nbsp;bytes;<ref>{{cite web |url=http://support.apple.com/kb/TS2419 |title=How OS X and iOS report storage capacity |publisher=Support.apple.com |date=2013-07-01 |access-date=2014-03-25 |url-status=live |archive-url=https://web.archive.org/web/20140304015219/http://support.apple.com/kb/TS2419 |archive-date=2014-03-04 }}</ref> file sizes are reported with decimal prefixes.<ref>{{cite web |url=http://support.apple.com/kb/TS2419 |title=How Mac OS X reports drive capacity |publisher=Apple Inc |date=2009-08-27 |access-date=2009-10-16 |url-status=live |archive-url=https://web.archive.org/web/20091222235620/http://support.apple.com/kb/TS2419 |archive-date=2009-12-22 }}</ref>
* {{As of|2016|post=,}} the binary interpretation was still used in marketing and billing by some telecommunication companies, such as [[Vodafone]],<ref>{{cite web|publisher=Vodafone Ireland|title=3G/GPRS data rates|url=https://www.vodafone.ie/planscosts_bus/data/|access-date=26 October 2016|url-status=live|archive-url=https://web.archive.org/web/20161026232743/https://www.vodafone.ie/planscosts_bus/data/|archive-date=26 October 2016}}</ref> [[AT&T]],<ref>{{cite web |publisher=AT&T |title=Data Measurement Scale |url=http://www.att.com/support_static_files/KB/KB24648.html |access-date=26 October 2016 }}{{dead link|date=December 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> [[Orange S.A.|Orange]]<ref>{{cite web|publisher=Orange Romania|title=Internet Mobile Access|url=https://www.orange.ro/recharge/internet.html|access-date=26 October 2016|url-status=dead|archive-url=https://web.archive.org/web/20161026234911/https://www.orange.ro/recharge/internet.html|archive-date=26 October 2016}}</ref> and [[Telstra]].<ref>{{cite web|publisher=Telstra|title=Our Customer Terms|page=7|url=https://www.telstra.com.au/content/dam/tcom/personal/consumer-advice/pdf/intl-roaming.pdf|access-date=26 October 2016|url-status=live|archive-url=https://web.archive.org/web/20170410020355/https://www.telstra.com.au/content/dam/tcom/personal/consumer-advice/pdf/intl-roaming.pdf|archive-date=10 April 2017}}</ref>

== Data examples ==
<!--{{quote frame|align=right|width=33%|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. 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 often 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%. The kibibyte is defined as 1024 bytes, avoiding the ambiguity issues of the kilobyte. When text is encoded in ASCII, each character is represented using a single byte, which means that for any given ASCII string the character count and byte count are the same. Incidentally, the passage of ASCII-encoded text you are reading right now is precisely one thousand characters; it's a kilobyte.}}-->
* The [[Lord's Prayer]], in Latin, is 296&nbsp;bytes (about 0.3 kilobytes).<ref>{{cite web|title=Vulgata Clementina|url=http://www.sacredbible.org/articles/Matthew-Latin3.htm|quote=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|access-date=2024-02-29|archive-date=2022-12-05|archive-url=https://web.archive.org/web/20221205102852/https://sacredbible.org/articles/Matthew-Latin3.htm|url-status=live}}</ref>
* The short story ''[[The Gift of the Magi]]'', by O. Henry, hosted on [[Project Gutenberg]] as an uncompressed plain text file,<ref>Minus the introductory and extroductory Gutenberg metatext</ref> is 11,203 characters; this is 11.2 kilobytes (dividing by 1,000) or 10.94 kibibytes (dividing by 1,024).<ref>{{Cite web|url=https://www.gutenberg.org/cache/epub/7256/pg7256.txt|title=The Gift of the Magi|first=O.|last=Henry|via=Project Gutenberg|access-date=2025-07-14}}</ref> ''[[The Cask of Amontillado]]'', by [[Edgar Allan Poe]], is 12,843&nbsp;bytes (12.8&nbsp;kilobytes or 12.5&nbsp;kibibytes).<ref>{{Cite web|url=https://www.gutenberg.org/files/25525/25525-h/25525-h.htm|title=The Cask of Amontillado|first=Edgar Allan|last=Poe|via=Project Gutenberg|access-date=2024-02-29|archive-date=2024-05-08|archive-url=https://web.archive.org/web/20240508202014/https://www.gutenberg.org/files/25525/25525-h/25525-h.htm|url-status=live}}</ref>
* The size of this article's wikitext source, as of {{CURRENTMONTHNAME}} {{CURRENTYEAR}}, is {{#expr:{{strip comma|{{PAGESIZE:Kilobyte}}}}/1000}} kilobytes.
* The novel ''[[The Picture of Dorian Gray]]'', by [[Oscar Wilde]], hosted on [[Project Gutenberg]] as an uncompressed plain text file, is 428,952&nbsp;bytes; this is 428.95&nbsp;kilobytes (428,952 divided by 1,000) and 418.90&nbsp;kibibytes (divided by 1,024).<!--428,952 bytes--> ''[[Great Expectations]]'' is 994,639&nbsp;bytes (994.639 kB),<!--993,639 bytes--><!-- Minus the table of contents (etc) and Gutenberg metatext at the beginning (505b) and end (18,527b). --><ref>{{Cite book|url=https://www.gutenberg.org/ebooks/1400|title=Great Expectations|first=Charles|last=Dickens|date=July 1, 1998|via=Project Gutenberg|access-date=February 29, 2024|archive-date=February 29, 2024|archive-url=https://web.archive.org/web/20240229212608/https://www.gutenberg.org/ebooks/1400|url-status=live}}</ref> and ''[[Moby Dick]]'' is 1,191,763&nbsp;bytes (1,191.763 kB).<!--1,191,763 bytes--><!-- Minus the prefaces and notes, and again minus the Gutenberg metatext at the beginning and end. --><ref>{{Cite book|url=https://www.gutenberg.org/ebooks/2701|title=Moby Dick; Or, The Whale|first=Herman|last=Melville|date=July 1, 2001|via=Project Gutenberg|access-date=February 29, 2024|archive-date=February 29, 2024|archive-url=https://web.archive.org/web/20240229214357/https://www.gutenberg.org/ebooks/2701|url-status=live}}</ref>

==See also==
{{cols}}
* [[Binary prefix]]
* {{Section link|Gigabyte|Consumer confusion}}
* [[History of the floppy disk]]
* {{Section link|JEDEC memory standards|Unit prefixes for semiconductor storage capacity}}
* [[Timeline of binary prefixes]]
* {{Section link|Units of information|Size examples}}
{{colend}}

==References==
{{Reflist|30em}}
* {{cite web |url=http://www.jedec.org/sites/default/files/docs/JESD100B01.pdf |title=Terms, Definitions, and Letter Symbols for Microcomputers, Microprocessors, and Memory Integrated Circuits |date=December 2002 |publisher=JEDEC Solid State Technology Association |access-date=22 September 2013 |archive-date=13 March 2016 |archive-url=https://web.archive.org/web/20160313053915/http://www.jedec.org/sites/default/files/docs/jesd100b01.pdf |url-status=live }}

{{Computer Storage Volumes}}

[[Category:Units of information]]