The
mebibyte (a contraction of
megabinary byte, pronounced MEH-bee-byte) is a standards-based
binary multiple (prefix
mebi-, symbol
Mi-) of the
byte, a unit of
digital information storage. Mebibyte is abbreviated
MiB.
The unit prefix
mebi was defined by the
International Electrotechnical Commission (IEC) in December 1998. Use of mebibyte and related units is 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 order to protect the unambiguous definition of the unit prefix
mega.
Megabyte is sometimes used in place of mebibyte, or to refer to 10
6 bytes = 1,000,000 bytes, or even 1,000 times 1,024 bytes, depending on context.
The historical binary interpretation of
mega is still in wide use by the consumer software industry and use of the
mebi prefix is still not common. This leads to
consumer confusion when 2
20 (1,048,576) bytes is referenced as 1 MB (megabyte) instead of 1 MiB. For example, the
operating system Windows XP shows a file of 2
20 bytes as "1.00 MB" in its file properties
dialog, while showing a file of 10
6 (1,000,000) bytes as "976 KB".
Apple's
Mac OS X 10.6, on the other hand, would report a 10
6 byte file correctly as "1 MB".
In another example, the
1.44 MB floppy disk's storage capacity is calculated using 1,024,000 bytes 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 three size designations are similar in value.
In
The Art of Computer Programming,
Donald Knuth proposed that this unit be called a
large megabyte (abbreviated
MMB), though this usage has never been common.
See also
