{{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}} {{Distinguish|megabit}} {{Infobox unit | name = megabyte | image = PS2-8MB-Mem-Card.jpg | caption = A PlayStation 2 memory card has a capacity of 8 megabytes (MB). | standard = Unit derived from bit | quantity = Digital information, data size | symbol = MB }} {{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 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 prefixes 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, 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 networking contexts and most storage media, particularly hard drives, 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 DVDs, and is also consistent with the other uses of the SI prefix in computing, such as CPU clock speeds or measures of performance. The Mac OS X 10.6 file manager is a notable example of this usage in software. Since 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 MB) is equal to one gigabyte (1 GB), where 1 GB is one billion bytes.
=== Base 2 === {{Main|Mebibyte}} : 1 MB = {{gaps|1|048|576}} bytes (= 1024<sup>2</sup> B = 2<sup>20</sup> 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 MB) is equal to one gigabyte (1 GB), where 1 GB is 1024<sup>3</sup> bytes (i.e., 1 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 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 disks 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. ~1152 × 864) with 256 colors (8 bits/pixel color depth) stored without any compression.<!-- (1024×1024×8)/8 = 1048576 bytes --> * 6{{nbsp}}seconds of 44.1 kHz/16 bit uncompressed CD audio.<!-- (44100×2×16/8)×6 = 1058400 bytes --> * 1{{nbsp}}minute of 128{{nbsp}}kbit/s MP3 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