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 = 1024 kibibytes. The unit symbol for the mebibyte is MiB. Technically a megabyte (MB) is a power of ten, while a mebibyte (MiB) is a power of two, appropriate for binary machines.

The unit was established by the International Electrotechnical Commission (IEC) in 1998.^[2] It was designed to replace the megabyte when used in the binary sense to mean 2²⁰ bytes, which conflicts 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 denotes 1000 × 1000 bytes. The discrepancy may cause confusion, since operating systems using the binary method report lower numerical values for storage size than advertised by manufacturers, such as disk drive manufacturers who strictly use decimal units.

History and usage

The binary prefixes, including mebi, were defined by the International Electrotechnical Commission (IEC) in December 1998. All major standards bodies have endorsed the use of them for binary multiples.

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.^[9][10]

Many operating systems compute file size in mebibytes, but report the number as MB (megabytes). 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.^[11][12]

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.^[13]

See also

• IEEE 1541
• Orders of magnitude (data)

References