Mebibyte

The mebibyte is a multiple of the unit byte for digital information.^[1] The binary prefix mebi means 2²⁰, therefore one mebibyte is equal to 1048576bytes. The unit symbol for the mebibyte is MiB.

The unit was established by the International Electrotechnical Commission (IEC) in 1998.^[2] It was designed to replace the megabyte, which is still being used in many contexts to represent 2²⁰ bytes, which is incompatible with the definition of the prefix mega in the International System of Units (SI) as a multiplier of 10⁶.

The binary prefixes have been accepted by all major standards organizations and are part of the International System of Quantities.^[3] Many Linux distributions use the unit, but it is not widely acknowledged within the industry or media.^[4][5][6][7]

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 × 1024 bytes,^[8] or 1048576bytes.

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 × 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 the Microsoft Windows operating system show a file of 2²⁰ bytes as "1.00 MB" or "1,024 KB" in its file properties dialog and show 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 instead uses megabytes for all file and disk sizes, so it reports a 10⁶ byte file as 1 MB.^[9][10]

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

The mebibyte is closely related to the megabyte. The latter term is often used as a synonym for mebibyte, but it formally refers to 1000 kilobytes, or 1,000,000 bytes. The binary prefix mebi, which is a factor of 2²⁰, was created to provide an unambiguous unit that is distinct from the metric SI prefix mega (M). Binary prefixes are becoming more predominant in scholarly literature, descriptions of computer hardware and open source software.^[12][13]

See also

• IEEE 1541
• Orders of magnitude (data)

References