View source for Megabyte

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{{Short description|Multiple of the unit byte}}
{{About|the decimal unit of data|binary unit of 1024{{sup|2}} bytes|mebibyte|other uses}}
{{Redirect|MByte|the battery electric car from ''Byton''|Byton M-Byte}}
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{{Quantities of bytes}}
The '''megabyte''' is a multiple of the unit [[byte]] for digital information. Its recommended unit symbol is '''MB'''.  The unit prefix ''mega'' is a multiplier of {{gaps|1|000|000}} (10<sup>6</sup>) in the [[International System of Units]] (SI).<ref name=bipm>{{cite web|url=http://www.bipm.org/en/si/si_brochure/chapter3/prefixes.html |title=SI Prefixes | website =  Bureau international des poids et mesures |access-date=June 1, 2007 |url-status=dead |archive-url=https://web.archive.org/web/20070607000414/http://www.bipm.org/en/si/si_brochure/chapter3/prefixes.html |archive-date=June 7, 2007 }}</ref> Therefore, one megabyte is one million bytes of information. This definition has been incorporated into the [[International System of Quantities]].

In the computer and information technology fields, other definitions have been used that arose for historical reasons of convenience. A common usage has been to designate one megabyte as {{gaps|1|048|576|bytes}} (2<sup>20</sup> B), a quantity that conveniently expresses the binary architecture of digital computer memory. Standards bodies have deprecated this binary usage of the mega- prefix in favor of a new set of [[binary prefixes]],<ref name="NIST">{{cite web |title=Definitions of the SI units: The binary prefixes |publisher=[[National Institute of Standards and Technology]] |url=http://physics.nist.gov/cuu/Units/binary.html }}</ref> by means of which the quantity 2<sup>20</sup> B is named [[mebibyte]] (symbol MiB).

==Definitions==
The unit megabyte is commonly used for 1000<sup>2</sup> (one million) bytes or 1024<sup>2</sup> bytes. The interpretation of using base 1024 originated as technical jargon for the byte [[SI prefix|multiples]] that needed to be expressed by the powers of 2 but lacked a convenient name. As 1024 (2<sup>10</sup>) approximates 1000 (10<sup>3</sup>), roughly corresponding to the SI prefix [[kilo-]], it was a convenient term to denote the binary multiple. In 1999, the [[International Electrotechnical Commission]] (IEC) published standards for [[binary prefix]]es requiring the use of ''megabyte'' to denote 1000<sup>2</sup> bytes, and ''[[mebibyte]]'' to denote 1024<sup>2</sup> bytes.  By the end of 2009, the IEC Standard had been adopted by the [[IEEE]], [[European Union|EU]], [[ISO]] and [[NIST]]. Nevertheless, the term megabyte continues to be widely used with different meanings.

=== Base 10 ===
: 1 MB = {{gaps|1|000|000}} bytes (= 1000<sup>2</sup> B = 10<sup>6</sup> B) is the definition following the rules of the [[International System of Units]] (SI), and the [[International Electrotechnical Commission]] (IEC).<ref name="NIST"/> This definition is used in [[computer network]]ing contexts and most [[storage media]], particularly [[hard drive]]s, [[Flash memory|flash]]-based storage,<ref>[https://web.archive.org/web/20080513155718/http://apac.sandisk.com/Products/Catalog(1349)-SanDisk_Extreme_Ducati_Edition_USB_Flash_Drive.aspx SanDisk USB Flash Drive] "Note: 1 megabyte (MB) = 1 million bytes; 1 gigabyte (GB) = 1 billion bytes."</ref> and [[DVD]]s, and is also consistent with the other uses of the [[SI prefix]] in computing, such as [[Megahertz#Megahertz in computing|CPU clock speeds]] or [[FLOPS|measures of performance]]. The [[Mac OS X]] 10.6 file manager is a notable example of this usage in software. Since [[Mac OS X Snow Leopard|Snow Leopard]], file sizes are reported in decimal units.<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}}</ref>
In this convention, one thousand megabytes (1000&nbsp;MB) is equal to one gigabyte (1&nbsp;GB), where 1&nbsp;GB is one billion bytes.

=== Base 2 ===
{{Main|Mebibyte}}
: 1 MB = {{gaps|1|048|576}} bytes (= 1024<sup>2</sup>&nbsp;B = 2<sup>20</sup>&nbsp;B) is the definition used by [[Microsoft Windows]] in reference to [[computer memory]], such as [[random-access memory]] (RAM). This definition is synonymous with the unambiguous binary unit [[mebibyte]]. In this convention, one thousand and twenty-four megabytes (1024&nbsp;MB) is equal to one gigabyte (1&nbsp;GB), where 1&nbsp;GB is 1024<sup>3</sup> bytes (i.e., 1&nbsp;[[Gibibyte|GiB]]).

=== Mixed ===
: 1 MB = {{gaps|1|024|000}} bytes (= 1000×1024 B) is the definition used to describe the formatted capacity of the 1.44&nbsp;MB {{gaps|3.5-inch}} HD [[floppy disk]], which actually has a capacity of {{gaps|1|474|560|bytes}}.<ref>[http://www.computernostalgia.net/articles/HistoryoftheFloppyDisk.htm Tracing the History of the Computer - History of the Floppy Disk]</ref>

Randomly addressable semiconductor memory doubles in size for each address lane added to an integrated circuit package, which favors counts that are powers of two. The capacity of a disk drive is the product of the sector size, number of sectors per track, number of tracks per side, and the number of disk platters in the drive. Changes in any of these factors would not usually double the size.

==Examples of use==
[[File:Imation 3.5" diskette 20050729.jpg|right|thumbnail|200px|1.44 MB [[floppy disk]]s can store 1,474,560 bytes of data. The full resolution image of this photograph of a floppy diskette is itself 0.842 megabytes.]]
Depending on compression methods and [[file format]], '''a megabyte of data''' can roughly be:
* a 1{{nbsp}}[[megapixel]] [[bitmap]] image (e.g. ~[[XGA+|1152&nbsp;×&nbsp;864]]) with 256 colors (8&nbsp;bits/pixel [[color depth]]) stored without any compression.<!-- (1024×1024×8)/8 = 1048576 bytes -->
* 6{{nbsp}}seconds of [[Compact Disc Digital Audio#Audio format|44.1&nbsp;kHz/16&nbsp;bit]] [[Audio file format#Uncompressed audio format|uncompressed]] CD audio.<!-- (44100×2×16/8)×6 = 1058400 bytes -->
* 1{{nbsp}}minute of 128{{nbsp}}[[Kilobits per second|kbit/s]] [[MP3]] [[Audio file format#Lossy compressed audio format|lossy compressed]] audio.<!-- (128000/8)×60 = 960000 bytes -->

The novel ''[[The Picture of Dorian Gray]]'', by [[Oscar Wilde]], hosted on [[Project Gutenberg]] as an uncompressed plain text file, is 0.429 MB<!--428,952 bytes-->. ''[[Great Expectations]]'' is 0.994 MB,<!--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}}</ref> and ''[[Moby Dick]]'' is 1.192 MB.<!--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}}</ref> 
The [[human genome]] consists of DNA representing 800{{nbsp}}MB of data. The parts that differentiate one person from another can be compressed to 4{{nbsp}}MB.<ref name="Christley">{{Cite journal | last1 = Christley | first1 = S. | last2 = Lu | first2 = Y. | last3 = Li | first3 = C. | last4 = Xie | first4 = X. | title = Human genomes as email attachments | doi = 10.1093/bioinformatics/btn582 | journal = Bioinformatics | volume = 25 | issue = 2 | pages = 274–275 | year = 2008 | pmid =  18996942| doi-access = free }}</ref>

==See also==
* [[Timeline of binary prefixes]]
* {{Section link|Gigabyte|Consumer confusion}}

==References==
{{reflist}}

==External links==
* [https://web.archive.org/web/20140728221058/http://ns1758.ca/winch/winchest.html Historical Notes About The Cost Of Hard Drive Storage Space]
* [http://searchstorage.techtarget.com/sDefinition/0,,sid5_gci212542,00.html the megabyte] (established definition in Networking and Storage industries; from [http://whatis.techtarget.com/definition/0,,sid9_gci551931,00.html whatis.com])
* [https://web.archive.org/web/20090403051731/http://www.iec.ch/zone/si/si_bytes.htm International Electrotechnical Commission definitions]
* [http://members.optus.net/alexey/prefBin.xhtml IEC prefixes and symbols for binary multiples] {{Webarchive|url=https://web.archive.org/web/20040615185053/http://members.optus.net/alexey/prefBin.xhtml |date=2004-06-15 }}

{{Computer Storage Volumes}}

[[Category:Units of information]]