Mebibyte

"MiB" redirects here. For similar abbreviations, see MIB (disambiguation).

The mebibyte is a multiple of the unit byte for digital information. The binary prefix mebi means 2²⁰; therefore one mebibyte is equal to 1048576bytes, i.e., 1024 kibibytes. The unit symbol for the mebibyte is MiB.

The unit was established by the International Electrotechnical Commission (IEC) in 1998. 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. Many Linux distributions use the unit, but it is not widely acknowledged within the industry or media.

Multiples of bytes
Decimal Value Metric 1 B byte 1000 kB kilobyte 10002 MB megabyte 10003 GB gigabyte 10004 TB terabyte 10005 PB petabyte 10006 EB exabyte 10007 ZB zettabyte 10008 YB yottabyte	Binary Value IEC JEDEC 1 B byte B byte 1024 KiB kibibyte KB kilobyte 10242 MiB mebibyte MB megabyte 10243 GiB gibibyte GB gigabyte 10244 TiB tebibyte – 10245 PiB pebibyte – 10246 EiB exbibyte – 10247 ZiB zebibyte – 10248 YiB yobibyte –
Orders of magnitude of data

Definition

1 MiB = 2²⁰ bytes = 1048576bytes = 1024 kibibytes

This definition implies that

1024 MiB = 1 gibibyte (GiB)

The prefix mebi is a binary prefix derived from the SI prefix mega- and the word binary. Its value is a binary (2ⁿ) approximation of 10⁶, the base-10 order of magnitude indicated by mega- in SI. One mebibyte (MiB) is 2²⁰, i.e. 1024 × 1024 bytes, 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 a megabyte. 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 mebibyte is closely related to the megabyte, which formally refers to 1,000,000 bytes. Within the field of computer science, during the 1970s and 1980s, the term megabyte generally meant 2 to the power 20 (1,048,576) bytes, but was sometimes used to mean 1,000,000 bytes. The errors associated with this ambiguity are relatively small with the lower prefixes in the series, i.e. for kilo and mega, but grows to substantial differences beyond.

In 1995, to resolve this ambiguity, the International Union of Pure and Applied Chemistry's Interdivisional Committee on Nomenclature and Symbols proposed new prefixes kibi, mebi, etc for powers of 1024. The mebi proposal was formally adopted by the International Electrotechnical Commission in December 1998, and published in January 1999.

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 2009 with 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.

The Ubuntu developer Canonical implemented an updated units policy in 2010 and as of Ubuntu 10.10 all versions use IEC binary prefixes for base-2 quantities and SI prefixes for base-10 quantities.

See also

• IEEE 1541
• Orders of magnitude (data)