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, appears increasingly in scientific literature and is now part of the International System of Quantities. . It has been adopted by Ubuntu and Linux, but has seen little further usage by the computer industry or in non-scientific literature. 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 hybrid not recognised by any standards body) 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.
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. 
The "Mi" (mebi-) binary prefix (which equals 220) was created to counter casual misuse of the "M" (mega-) decimal prefix (which equals 106). An example of such casual misuse is the marking of 3½-inch HD floppy disks. While they have an actual capacity of 1474560bytes, they have usually been marked "1.44 MB" in error. The error is this: Though 1474560bytes does equal 1440 KiB, 1440 KiB cannot be designated "1.44 MB" because doing so mixes binary and decimal prefixes. The resulting mixed prefix-base creates a quantity that is not only confusing, it is non-calculable. To maintain consistent prefix-base, 1440 KiB must be designated either "1.40625 MiB" (possibly rounded to "1.41 MiB") or 1.47456 MB (possibly rounded to "1.47 MB"). Lower capacity predecessors of this disquette include versions able to store 720 KiB (designated "720 KB") and 360 KiB (designated "360 KB").
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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