Mebibyte

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Prefixes for bit and byte
Decimal
Value SI
10001 k kilo-
10002 M mega-
10003 G giga-
10004 T tera-
10005 P peta-
10006 E exa-
10007 Z zetta-
10008 Y yotta-
Binary
Value IEC JEDEC
10241 Ki kibi- K kilo-
10242 Mi mebi- M mega-
10243 Gi gibi- G giga-
10244 Ti tebi-
10245 Pi pebi-
10246 Ei exbi-
10247 Zi zebi-
10248 Yi yobi-

A mebibyte (a contraction of mega binary byte) is a unit of information or computer storage, abbreviated MiB.

1 MiB = 220 bytes = 1,048,576 bytes = 1,024 kibibytes

The mebibyte is closely related to the megabyte (MB), which can be a synonym for mebibyte, or refer to 106 bytes = 1,000,000 bytes, or even refer to 1,000 times 1,024 bytes, depending on context (see binary prefix for background). The 1.44 MB floppy disk's storage capacity is calculated using 1,024,000 bytes per "MB" (e.g. 1.44 times 1024 times 1000), rather than 1.44 mebibytes (1.44 times 1,048,576). The three numbers are relatively close together, but mistaking the three has nonetheless led to consumer confusion and even legal disputes. There are times when it is necessary to know the exact size of a file, for example, or exactly how much space remains on a storage device.

The unit was defined by the International Electrotechnical Commission (IEC) in December 1998. Use of mebibyte and related units is endorsed by IEEE and CIPM in contexts where use of a binary prefix makes sense, in order to protect the unambiguous decimal meaning of the "mega" prefix. The binary unit is in wide use by the consumer software industry, but use of the "mebi-" prefix is not. This leads to confusion where 220 (1,048,576) bytes is displayed as 1 MB instead of 1 MiB. For example, the operating system Windows XP will show a file of 220 bytes as "1.00 MB" in its file properties dialog. Likewise, a file of 106 (1,000,000) bytes is reported as "976 KB".

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