The
mebibyte is a multiple of the unit
byteThe byte is a unit of digital information in computing and telecommunications that most commonly consists of eight bits. Historically, a byte was the number of bits used to encode a single character of text in a computer and for this reason it is the basic addressable element in many computer...
for digital
informationInformation in its most restricted technical sense is a message or collection of messages that consists of an ordered sequence of symbols, or it is the meaning that can be interpreted from such a message or collection of messages. Information can be recorded or transmitted. It can be recorded as...
. The
binary prefixIn computing, a binary prefix is a specifier or mnemonic that is prepended to the units of digital information, the bit and the byte, to indicate multiplication by a power of 2...
mebi means 2
20, therefore 1
mebibyte is . The unit symbol for the mebibyte is
MiB. The unit was established by the
International Electrotechnical CommissionThe International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...
(IEC) in 2000 and has been accepted for use by all major standards organizations. It was designed to replace the
megabyteThe megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...
used in some computer science contexts to mean 2
20 bytes, which is similar to but conflicts with the
SIThe International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...
definition of the prefix mega (10
6).
Definition
- 1 MiB = 220 byte
The byte is a unit of digital information in computing and telecommunications that most commonly consists of eight bits. Historically, a byte was the number of bits used to encode a single character of text in a computer and for this reason it is the basic addressable element in many computer...
s = 1024 kibibyteThe kibibyte is a multiple of the unit byte for quantities of digital information. The binary prefix kibi means 1024; therefore, 1 kibibyte is . The unit symbol for the kibibyte is KiB. The unit was established by the International Electrotechnical Commission in 1999 and has been accepted for use...
s =
The prefix
mebi is a
binary prefixIn computing, a binary prefix is a specifier or mnemonic that is prepended to the units of digital information, the bit and the byte, to indicate multiplication by a power of 2...
derived from the words mega and binary, indicating its origin in the closeness in value to the
SI prefixThe International System of Units specifies a set of unit prefixes known as SI prefixes or metric prefixes. An SI prefix is a name that precedes a basic unit of measure to indicate a decadic multiple or fraction of the unit. Each prefix has a unique symbol that is prepended to the unit symbol...
mega. One mebibyte (MiB) is 2
20 (i.e., 1024 x 1024) bytes, or . One MiB differs from one
megabyteThe megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...
(MB), which means 10
6 (i.e. 1000 x 1000 = ).
Mebibyte is not commonly used. Instead,
megabyte is often used to mean 1000 x 1000, 1024 x 1024, and even 1000 x 1024 bytes. Such usage can be confusing and inconsistent. For example, Microsoft's
Windows XPWindows XP is an operating system produced by Microsoft for use on personal computers, including home and business desktops, laptops and media centers. First released to computer manufacturers on August 24, 2001, it is the second most popular version of Windows, based on installed user base...
operating systemAn operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
shows a file of 2
20 bytes as "1.00 MB" in its file properties
dialogIn a graphical user interface of computers, a dialog box is a type of window used to enable reciprocal communication or "dialog" between a computer and its user. It may communicate information to the user, prompt the user for a response, or both...
, while showing a file of 10
6 bytes as 976 KB; but Apple's
Mac OS XMac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
10.6 would report a 10
6 byte file as 1 MB.
History
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 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 CommissionThe International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...
(IEC) in December 1998. Its use (and related units) is presently endorsed by the
Institute of Electrical and Electronics EngineersThe Institute of Electrical and Electronics Engineers is a non-profit professional association headquartered in New York City that is dedicated to advancing technological innovation and excellence...
(IEEE) and the
International Committee for Weights and MeasuresThe Interglobal Committee for Weights and Measures is the English name of the Comité international des poids et mesures . It consists of eighteen persons from Member States of the Metre Convention...
(CIPM) in contexts where use of a
binary prefixIn computing, a binary prefix is a specifier or mnemonic that is prepended to the units of digital information, the bit and the byte, to indicate multiplication by a power of 2...
makes sense.
In
The Art of Computer ProgrammingThe Art of Computer Programming is a comprehensive monograph written by Donald Knuth that covers many kinds of programming algorithms and their analysis....
,
Donald KnuthDonald Ervin Knuth is a computer scientist and Professor Emeritus at Stanford University.He is the author of the seminal multi-volume work The Art of Computer Programming. Knuth has been called the "father" of the analysis of algorithms...
proposed that the mebibyte be called a
large megabyte (abbreviated
MMB).