Mebibyte

The mebibyte is a multiple of the unit byte for digital information. The binary prefix mebi means 220; therefore 1 mebibyte is 1048576bytes. The unit symbol for the mebibyte is MiB.[1] The unit was established by the International Electrotechnical Commission (IEC) in 1998.[2] It was designed to replace the megabyte used in some computer science contexts to mean 220 bytes, which is similar to the SI definition of the prefix mega (106) but conflicts with it.

The unit has been accepted for use by all major standards organizations, appears increasingly in scholarly literature and is part of the International System of Quantities.[3] Many Linux distributions use the unit, but the unit has not been widely accepted in the computer industry or popular media.[4][5][6][7] The unit megabyte (symbol MB), formally meaning 1000000bytes, is still commonly used in place of this unit.

Multiples of bytes
Decimal
Value Metric
1000 kB kilobyte
10002 MB megabyte
10003 GB gigabyte
10004 TB terabyte
10005 PB petabyte
10006 EB exabyte
10007 ZB zettabyte
10008 YB yottabyte
Binary
Value JEDEC IEC
1024 KB kilobyte KiB kibibyte
10242 MB megabyte MiB mebibyte
10243 GB gigabyte GiB gibibyte
10244 – – TiB tebibyte
10245 – – PiB pebibyte
10246 – – EiB exbibyte
10247 – – ZiB zebibyte
10248 – – YiB yobibyte
Orders of magnitude of data

Definition

1 MiB = 220 bytes = 1024 kibibytes = 1048576bytes

The prefix mebi is a binary prefix derived from the words mega and binary, indicating its origin in the closeness in value to the SI prefix mega. One mebibyte (MiB) is 220 (i.e. 1024 x 1024) bytes,[8] or 1048576bytes. One MiB differs from one megabyte (MB), which means 106 (i.e. 1000 x 1000 = 1000000) bytes.

Despite its official status, the unit mebibyte is not commonly used even when reporting byte counts calculated in binary multiples, but is often represented as megabytes. Formally, one megabyte means 1000 x 1000 bytes. Disk drive manufacturers strictly use decimal units, and the megabyte means 1000000bytes. The discrepancy may cause confusion, since operating systems using the binary method report lower numerical values for storage size than advertised by manufacturers. Many operating systems compute file size in mebibytes, but report the number as MB. For example, all versions of Microsoft Windows operating system shows a file of 220 bytes as "1.00 MB" or "1,024 KB" in its file properties dialog, while showing a file of 106 (1000000) bytes as 976 KB.

All versions of Apple's operating systems had the same behavior, until Mac OS X version 10.6, which now uses megabytes for all file and disk sizes, so it reports a 106 byte file as 1 MB.[9][10]

Ubuntu developer Canonical implemented an updated Units Policy in 2010 and as of Ubuntu 10.10 all versions now adhere to the IEC binary prefix for base-2 units and the SI prefix for base-10 units. [11]

History

The binary prefix mebi, which is a factor of 220, was created to provide an unambiguous unit distinct from the metric SI prefix mega (M), which represents multiplication by 106. An example of such misuse is the marking of 3½-inch HD floppy disks. They have usually been marked 1.44 MB, while their true capacity of 1474560bytes is equal to 1440 KiB. Lower capacity predecessors of this diskette include versions with capacities of 720 KiB (designated "720 KB") and 360 KiB (designated "360 KB").

The prefix mebi was defined by the International Electrotechnical Commission (IEC) in December 1998. The use of the binary prefixes has been endorsed by all major international standards bodies.

In The Art of Computer Programming, Donald Knuth proposed that the mebibyte be called a large megabyte (abbreviated MMB).

Binary prefixes are increasingly used in scholarly literature and open source software.

See also

References

  1. ↑ International Electrotechnical Commission (January 2010). "IEC 60050 - International Electrotechnical Vocabulary - Details for IEV number 112-01-27". Retrieved 2011-06-19.
  2. ↑ International Electrotechnical Commission (January 1999), IEC 60027-2 Amendment 2: Letter symbols to be used in electrical technology - Part 2: Telecommunications and electronics.
  3. ↑ "IEC 80000-13:2008". International Organization for Standardization. Retrieved 21 July 2013.
  4. ↑ Upgrading and Repairing PCs, Scott Mueller, Pg. 596, ISBN 0-7897-2974-1
  5. ↑ The silicon web: physics for the Internet age, Michael G. Raymer, Pg. 40, ISBN 978-1-4398-0311-0
  6. ↑ Knuth: Recent News. Cs-staff.stanford.edu. Retrieved on 2011-01-07.
  7. ↑ Atwood, Jeff. (2007-09-10) Gigabyte: Decimal vs. Binary. Coding Horror. Retrieved on 2011-01-07.
  8. ↑ "Definition of NIST binary". Ziff-Davis. 2010. Retrieved 2010-07-31.
  9. ↑ "How Mac OS X reports drive capacity". Apple Inc. 2009-08-27. Retrieved 2009-10-16.
  10. ↑ David Pogue (2011), Mac OS X Lion: The Missing Manual Missing Manual, Oreilly Series, O'Reilly Media, pp. 473–474, ISBN 978-1-4493-9749-4
  11. ↑ "Ubuntu UnitsPolicy". Ubuntu. 2010. Retrieved 2013-09-26.