The mebibyte is a multiple of the unit byte for digital information. The binary prefix mebi means 220; therefore 1 mebibyte is 1048576 bytes. 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 used in some computer science contexts to mean 220 bytes, which is similar to the SI definition of the prefix mega (106) but conflicts with it.
The unit has been accepted for use by all major standards organizations, and appears increasingly in scientific literature. It has seen little usage in non-scientific literature or by the computer industry. The unit megabyte (symbol MB), formally meaning 1000000bytes, is still commonly used in place of this unit.
|Orders of magnitude of data|
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 x 1024) bytes, or 1048576bytes. One MiB differs from one megabyte (MB), which means 106 (i.e. 1000 x 1000 = 1000000) bytes.
The term mebibyte is not commonly used even when reporting numbers calculated as mebibytes. Instead, megabyte is often used to mean 1000 x 1000 (correctly used), 1024 x 1024 (properly mebibytes) or even 1024 x 1000 (a strange hybrid) by operating system and utility software. Disk drive manufacturers generally use megabyte correctly to mean 1,000,000 bytes. The inconsistency can be confusing, since operating systems using the nonstandards-based method report lower numbers for hard disks than advertised by manufacturers. Many operating systems compute file size in mebibytes, but report the number as MB. For example, all versions of Microsoft Windows operating system shows a file of 220 bytes as "1.00 MB" or "1,024 KB" in its file properties dialog, while showing a file of 106 (1000000) bytes as 976 KB.
Confusion in the meaning of megabyte was evident for many years. For instance, the 1.44 MB floppy disk's storage capacity was calculated using 1024000bytes 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 mebi- prefix was defined by the International Electrotechnical Commission (IEC) in December 1998. Its use (and related units) is presently 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.
Binary prefixes are increasingly used in scientific literature and open source software. In product advertising and other non-scientific publications, the kilobyte sometimes refers to a power of ten and sometimes a power of two. 
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