Mebibyte

"MiB" redirects here. For other things abbreviating to MiB or MIB, see MIB (disambiguation).

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 2000 and has been accepted for use by all major standards organizations. It was designed to replace the megabyte used in some computer science contexts to mean 2²⁰ bytes, which is similar to but conflicts with the SI definition of the prefix mega (10⁶).

v · d · e Multiples of bytes
SI decimal prefixes		IEC binary prefixes
Name (Symbol)	Value	Name (Symbol)	Value
kilobyte (kB)	103	kibibyte (KiB)	210 = 1.024 × 103
megabyte (MB)	106	mebibyte (MiB)	220 ≈ 1.049 × 106
gigabyte (GB)	109	gibibyte (GiB)	230 ≈ 1.074 × 109
terabyte (TB)	1012	tebibyte (TiB)	240 ≈ 1.100 × 1012
petabyte (PB)	1015	pebibyte (PiB)	250 ≈ 1.126 × 1015
exabyte (EB)	1018	exbibyte (EiB)	260 ≈ 1.153 × 1018
zettabyte (ZB)	1021	zebibyte (ZiB)	270 ≈ 1.181 × 1021
yottabyte (YB)	1024	yobibyte (YiB)	280 ≈ 1.209 × 1024
See also: Multiples of bits · 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,^[2] or 1048576bytes. One MiB differs from one megabyte (MB), which means 10⁶ (i.e. 1000 x 1000 = 1000000bytes).

Mebibyte is not commonly used. Instead, megabyte is often used to mean 1000 x 1000, 1024 x 1024, and even 1000 x 1024 bytes. Such usage can be confusing and inconsistent. For example, Microsoft's Windows XP operating system shows a file of 2²⁰ bytes as "1.00 MB" in its file properties dialog, while showing a file of 10⁶ (1000000) bytes as 976 KB; but Apple's Mac OS X 10.6 would report a 10⁶ byte file as 1 MB.^[3]

History

Confusion in the meaning of megabyte was evident for many years. For instance, the 1.44 MB floppy disk's storage capacity was calculated using 1024000bytes per "MB" (i.e. 1.44×1024×1000), rather than 1.47 MB (1.47×1000×1000) or 1.40 MiB (1.40×1024×1024).

The mebi- prefix was defined by the International Electrotechnical Commission (IEC) in December 1998. Its use (and related units) is presently endorsed by the Institute of Electrical and Electronics Engineers (IEEE) and the International Committee for Weights and Measures (CIPM) in contexts where use of a binary prefix makes sense.

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

See also

• Megabyte
• SI prefix
• IEEE 1541
• Orders of magnitude (data)

References

1. ^ International Electrotechnical Commission (2010-01). "IEC 60050 - International Electrotechnical Vocabulary - Details for IEV number 112-01-27". http://www.electropedia.org/iev/iev.nsf/display?openform&ievref=112-01-27. Retrieved 2011-06-19. 
2. ^ "Definition of NIST binary". Ziff-Davis. 2010. http://www.pcmag.com/encyclopedia_term/0,2542,t=mebi&i=55970,00.asp. Retrieved 2010-07-31. 
3. ^ "How Mac OS X reports drive capacity". Apple Inc. 2009-08-27. http://support.apple.com/kb/TS2419. Retrieved 2009-10-16.