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, i.e., 1024 kibibytes. The unit symbol for the mebibyte is MiB.

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]


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,[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 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 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 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.[11][12]

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.[13]

See also


  1. ^ International Electrotechnical Commission (January 2010). "IEC 60050 - International Electrotechnical Vocabulary - Details for IEV number 112-01-27". Retrieved 2011-06-19.
  2. ^ International Electrotechnical Commission (January 1999), IEC 60027-2 Amendment 2: Letter symbols to be used in electrical technology - Part 2: Telecommunications and electronics.[1]
  3. ^ "IEC 80000-13:2008". International Organization for Standardization. Retrieved 21 July 2013.
  4. ^ Upgrading and Repairing PCs, Scott Mueller, Pg. 596, ISBN 0-7897-2974-1
  5. ^ The silicon web: physics for the Internet age, Michael G. Raymer, Pg. 40, ISBN 978-1-4398-0311-0
  6. ^ Knuth: Recent News. Retrieved on 2011-01-07.
  7. ^ Atwood, Jeff. (2007-09-10) Gigabyte: Decimal vs. Binary. Coding Horror. Retrieved on 2011-01-07.
  8. ^ "Definition of NIST binary". Ziff-Davis. 2010. Retrieved 2010-07-31.
  9. ^ HDD Turns 50 Years Today - The Chronicles
  10. ^ Backman, R. B. (2004). The Description, Evolution, and Applications of Binary Prefixes.
  11. ^ "How Mac OS X reports drive capacity". Apple Inc. 2009-08-27. Retrieved 2009-10-16.
  12. ^ David Pogue (2011), Mac OS X Lion: The Missing Manual Missing Manual, Oreilly Series, O'Reilly Media, pp. 473–474, ISBN 978-1-4493-9749-4
  13. ^ "Ubuntu UnitsPolicy". Ubuntu. 2010. Retrieved 2013-09-26.
Binary prefix

A binary prefix is a unit prefix for multiples of units in data processing, data transmission, and digital information, notably the bit and the byte, to indicate multiplication by a power of 2.

The computer industry has historically used the units kilobyte, megabyte, and gigabyte, and the corresponding symbols KB, MB, and GB, in at least two slightly different measurement systems. In citations of main memory (RAM) capacity, gigabyte customarily means 1073741824 bytes. As this is a power of 1024, and 1024 is a power of two (210), this usage is referred to as a binary measurement.

In most other contexts, the industry uses the multipliers kilo, mega, giga, etc., in a manner consistent with their meaning in the International System of Units (SI), namely as powers of 1000. For example, a 500 gigabyte hard disk holds 500000000000 bytes, and a 1 Gbit/s (gigabit per second) Ethernet connection transfers data at 1000000000 bit/s. In contrast with the binary prefix usage, this use is described as a decimal prefix, as 1000 is a power of 10 (103).

The use of the same unit prefixes with two different meanings has caused confusion. Starting around 1998, the International Electrotechnical Commission (IEC) and several other standards and trade organizations addressed the ambiguity by publishing standards and recommendations for a set of binary prefixes that refer exclusively to powers of 1024. Accordingly, the US National Institute of Standards and Technology (NIST) requires that SI prefixes only be used in the decimal sense: kilobyte and megabyte denote one thousand bytes and one million bytes respectively (consistent with SI), while new terms such as kibibyte, mebibyte and gibibyte, having the symbols KiB, MiB, and GiB, denote 1024 bytes, 1048576 bytes, and 1073741824 bytes, respectively. In 2008, the IEC prefixes were incorporated into the international standard system of units used alongside the International System of Quantities (see ISO/IEC 80000).

Data-rate units

In telecommunications, data-transfer rate is the average number of bits (bitrate), characters or symbols (baudrate), or data blocks per unit time passing through a communication link in a data-transmission system. Common data rate units are multiples of bits per second (bit/s) and bytes per second (B/s). For example, the data rates of modern residential high-speed Internet connections are commonly expressed in megabits per second (Mbit/s).


The exbibyte (symbol EiB) is 260 bytes of digital information. It is one of a set of units with binary prefixes defined by the International Electrotechnical Commission (IEC).The prefix exbi (symbol Ei) represents multiplication by 260, therefore:

1 exbibyte = 260 bytes = 1152921504606846976bytes = 1024pebibytesThe exbibyte is approximately equal to 1.15 exabytes (EB), the corresponding unit in the decimal system of multiples, which is defined as 1018 bytes = 1000000000000000000bytes.

One exbibyte (1 EiB) is equal to eight exbibits (8 Eibit).

One thousand twenty-four exbibytes (1024 EiB) is equal to one zebibyte (1 ZiB).

File size

File size is a measure of how much data a computer file contains or, alternately, how much storage it consumes. Typically, file size is expressed in units of measurement based on the byte. By convention, file size units use either a metric prefix (as in megabyte and gigabyte) or a binary prefix (as in mebibyte and gibibyte).When a file is written to a file system, which is the case in most modern devices, it may consume slightly more disk space than the file requires. This is because the file system rounds the size up to include any unused space left over in the last disk sector used by the file. (A sector is the smallest amount of space addressable by the file system. The size of a disk sectors is several hundred or several thousands bytes.) The wasted space is called slack space or internal fragmentation. Although smaller sector sizes allow for denser use of disk space, they decrease the operational efficiency of the file system.

The maximum file size a file system supports depends not only on the capacity of the file system, but also on the number of bits reserved for the storage of file size information. The maximum file size in the FAT32 file system, for example, is 4,294,967,295 bytes, which is one byte less than four gibibytes.

Kilobyte (KB) (JEDEC), is sometimes referred to unambiguously as kibibyte (KiB)(IEC). Sometimes kB, with lower cased SI-prefix k- for kilo (1000), is used, then always equaling 1000 bytes.

A file system may display all sizes with the metric system with only kB on small files indicating it, while some file systems/operating systems would display sizes in, the traditionally used on computers, binary system for all sizes, e.g. KB, even if hard disk manufacturers may prefer to use the metric system (for e.g. GB = 1,000,000,000 bytes and TB = 1000 GB), to show higher capacity numbers for their products.

File transfers (e.g. "downloads") may use rates of units of bytes (e.g. MB/s) in binary rather than metric system, while networking hardware, such as WiFi, always uses the metric system (Mbits/s, Gbits/s etc.). of units of bits (and it needs to send more than the files themselves, so some overhead needs to be factored in), making superficially similar terms very incompatible.


The gibibyte is a multiple of the unit byte for digital information. The binary prefix gibi means 230, therefore one gibibyte is equal to 1073741824bytes = 1024 mebibytes. The unit symbol for the gibibyte is GiB.

It is one of the units with binary prefixes defined by the International Electrotechnical Commission (IEC) in 1998.The gibibyte is closely related to the gigabyte (GB), which is defined by the IEC as 109 bytes = 1000000000bytes, 1GiB ≈ 1.074GB. 1024 gibibytes are equal to one tebibyte. In the context of computer memory, gigabyte and GB are customarily used to mean 10243 (230) bytes, although not in the context of data transmission and not necessarily for hard drive size.Hard drive and SSD manufacturers use the gigabyte to mean 1000000000 bytes. Therefore, the capacity of a 128 GB SSD is 128000000000 bytes. Expressed in gibibytes this is about 119.2 GiB. Some operating systems, including Microsoft Windows, display such a drive capacity as 119 GB, using the SI prefix G with the binary meaning. No space is missing: the size is simply being expressed in a different unit, even though the same prefix (G) is used in both cases.

The use of gigabyte (GB) to refer to 1000000000 bytes in some contexts and to 1073741824 bytes in others, sometimes in reference to the same device, has led to claims of confusion, controversies, and lawsuits. The IEC created the binary prefixes (kibi, mebi, gibi, etc.) in an attempt to reduce such confusion. They are increasingly used in technical literature and open-source software, and are a component of the International System of Quantities.


The gigabyte () is a multiple of the unit byte for digital information. The prefix giga means 109 in the International System of Units (SI). Therefore, one gigabyte is 1000000000bytes. The unit symbol for the gigabyte is GB.

This definition is used in all contexts of science, engineering, business, and many areas of computing, including hard drive, solid state drive, and tape capacities, as well as data transmission speeds. However, the term is also used in some fields of computer science and information technology to denote 1073741824 (10243 or 230) bytes, particularly for sizes of RAM. The use of gigabyte may thus be ambiguous. Hard disk capacities as described and marketed by drive manufacturers using the standard metric definition of the gigabyte, but when a 500-GB drive's capacity is displayed by, for example, Microsoft Windows, it is reported as 465 GB, using a binary interpretation.

To address this ambiguity, the International System of Quantities standardizes the binary prefixes which denote a series of integer powers of 1024. With these prefixes, a memory module that is labeled as having the size 1GB has one gibibyte (1GiB) of storage capacity.


The kibibyte is a multiple of the unit byte for quantities of digital information. The binary prefix kibi means 210, or 1024; therefore, 1 kibibyte is 1024 bytes. The unit symbol for the kibibyte is KiB.The unit was established by the International Electrotechnical Commission (IEC) in 1998, has been accepted for use by all major standards organizations, and is part of the International System of Quantities. The kibibyte was designed to replace the kilobyte in those computer science contexts in which the term kilobyte is used to mean 1024 bytes. The interpretation of kilobyte to denote 1024 bytes, conflicting with the SI definition of the prefix kilo (1000), used to be common.


The mebibit is a multiple of the bit, a unit of information, prefixed by the standards-based multiplier "mebi" (symbol Mi), a binary prefix meaning 220. The unit symbol of the mebibit is Mibit.

1 mebibit = 220 bits = 1048576bits = 1024 kibibitsThis unit is most useful for measuring RAM and ROM chip capacity.

The mebibit is closely related to the megabit which equals 106 bits = 1,000,000 bits.

Throughout the 1980s and 1990s, video game manufacturers sometimes reported the amount of internal cartridge read-only memory (ROM) on packaging in megabits, where 1 megabit equaled 128 kibibyte and 8 megabits were 1 mebibyte of ROM, containing game instructions and data.


Mega is a unit prefix in metric systems of units denoting a factor of one million (106 or 1000000). It has the unit symbol M. It was confirmed for use in the International System of Units (SI) in 1960. Mega comes from Ancient Greek: μέγας, translit. megas, lit. 'great'.


The megabyte is a multiple of the unit byte for digital information. Its recommended unit symbol is MB. The unit prefix mega is a multiplier of 1000000 (106) in the International System of Units (SI). Therefore, one megabyte is one million bytes of information. This definition has been incorporated into the International System of Quantities.

However, in the computer and information technology fields, several other definitions are used that arose for historical reasons of convenience. A common usage has been to designate one megabyte as 1048576bytes (220 B), a measurement that conveniently expresses the binary multiples inherent in digital computer memory architectures. However, most standards bodies have deprecated this usage in favor of a set of binary prefixes, in which this quantity is designated by the unit mebibyte (MiB). Less common is a convention that used the megabyte to mean 1000×1024 (1024000) bytes.

Megabyte (disambiguation)

Megabyte (MB) is a decimallized unit of data storage measurement equalling 106 bytes.

Megabyte may also refer to:

Mebibyte (MiB), the idiomatic unit of data storage measurement, also called "megabyte" (MB), equalling 220 bytes.

Megabyte (ReBoot), a fictional character from the CG animated TV fictional universe ReBoot

MEGABYTE Act of 2016 (Making Electronic Government Accountable By Yielding Tangible Efficiencies) H.R. 4904, a federal law of the United States of America

Orders of magnitude (bit rate)

An order of magnitude is generally a factor of ten. A quantity growing by four orders of magnitude implies it has grown by a factor of 10000 or 104. However, because computers are binary, orders of magnitude are sometimes given as powers of two.

This article presents a list of multiples, sorted by orders of magnitude, for bit rates measured in bits per second. Since some bit rates may measured in other quantities of data or time (like MB/s), information to assist with converting to and from these formats is provided. This article assumes the following:

A group of 8 bits (8 b) constitutes one byte (1 B). The byte is the most common unit of measurement of information (megabyte, mebibyte, gigabyte, gibibyte, etc.).

The decimal SI prefixes kilo, mega etc., are powers of 10. The power of two equivalents are the binary prefixes kibi, mebi, etc.Accordingly:

1 kB (kilobyte) = 1000 bytes = 8000 bits

1 KiB (kibibyte) = 210 bytes = 1024 bytes = 8192 bits

1 kb (kilobit) = 125 bytes = 1000 bits

1 Kib (kibibit) = 210 bits = 1024 bits = 128 bytes

Orders of magnitude (data)

An order of magnitude is a factor of ten. A quantity growing by four orders of magnitude implies it has grown by a factor of 10,000 or 104.

This article presents a list of multiples, sorted by orders of magnitude, for digital information storage measured in bits.

The byte is a common unit of measurement of information (kilobyte, kibibyte, megabyte, mebibyte, gigabyte, gibibyte, terabyte, tebibyte, etc.); for the purpose of this article, a byte is a group of 8 bits (octet), a nibble is a group of four bits. Historically, both assumptions have not always been true.

The decimal SI prefixes kilo, mega, giga, tera, etc., are powers of 103 = 1000. The binary prefixes kibi, mebi, gibi, tebi, etc. respectively refer to the corresponding power of 210 = 1024. In casual usage, when 1024 is a close enough approximation of 1000, the two corresponding prefixes are equivalent.

Note: this page mixes between two kinds of entropies:

Entropy (information theory), such as the amount of information that can be stored in DNA

Entropy (thermodynamics), such as entropy increase of 1 mole of waterThese two definitions are not entirely equivalent, see Entropy in thermodynamics and information theory.

For comparison, the Avogadro constant is 6.02214179(3)×1023 entities per mole, based upon the number of atoms in 12 grams of carbon-12 isotope.

In 2012, some hard disks used ~984,573 atoms to store each bit. In January 2012, IBM researchers announced they compressed 1 bit in 12 atoms using antiferromagnetism and a scanning tunneling microscope with iron and copper atoms. This could mean a practical jump from a 1 TB disk to a 100 TB disk.


The pebibyte is a multiple of the unit byte for digital information. It is a member of the set of units with binary prefixes defined by the International Electrotechnical Commission (IEC). Its unit symbol is PiB.

The prefix pebi (symbol Pi) represents multiplication by 10245, therefore:

1 pebibyte = 250 bytes = 1125899906842624bytes = 1024 tebibytesThe pebibyte is closely related to the petabyte (PB), its corresponding unit in the decimal set of multiples defined in the International System of Units (SI), and which represents 1015 bytes = 1000000000000000bytes. It follows that one pebibyte (1 PiB) is approximately equal to 1.13 PB.

One pebibyte (1 PiB) is equal to eight pebibits (8 Pibit).

One thousand twenty-four pebibytes (1024 PiB) is equal to one exbibyte (1 EiB).

Real mode

Real mode, also called real address mode, is an operating mode of all x86-compatible CPUs. Real mode is characterized by a 20-bit segmented memory address space (giving exactly 1 MiB of addressable memory) and unlimited direct software access to all addressable memory, I/O addresses and peripheral hardware. Real mode provides no support for memory protection, multitasking, or code privilege levels.

Before the release of the 80286, which introduced protected mode, real mode was the only available mode for x86 CPUs; and for backward compatibility, all x86 CPUs start in real mode when reset, though it is possible to emulate real mode on other systems when starting on other modes.


The tebibyte is a multiple of the unit byte for digital information. It is a member of the set of units with binary prefixes defined by the International Electrotechnical Commission (IEC). Its unit symbol is TiB.

The prefix tebi (symbol Ti) represents multiplication by 10244, therefore:

1 tebibyte = 240 bytes = 1099511627776bytes = 1024 gibibytes1024 TiB = 1 pebibyte (PiB)The tebibyte is closely related to the terabyte (TB), which is defined as 1012 bytes = 1000000000000bytes. It follows that one tebibyte (1 TiB) is approximately equal to 1.1 TB.

In some contexts, the terabyte has been used as a synonym for tebibyte. (see Consumer confusion).


The terabyte is a multiple of the unit byte for digital information. The prefix tera represents the fourth power of 1000, and means 1012 in the International System of Units (SI), and therefore one terabyte is one trillion (short scale) bytes. The unit symbol for the terabyte is TB.


The yobibyte is a multiple of the unit byte for digital information. It is a member of the set of units with binary prefixes defined by the International Electrotechnical Commission (IEC). Its unit symbol is YiB

The prefix yobi (symbol Yi) represents multiplication by 10248, therefore:

1 yobibyte = 280 bytes = 1208925819614629174706176bytes = 1024 zebibytesThe prefixes zebi and yobi were added to the system of binary prefixes in August 2005.One yobibyte (1 YiB) is equal to eight yobibits (8 Yibit).


The yottabyte is a multiple of the unit byte for digital information. The prefix yotta indicates multiplication by the eighth power of 1000 or 1024 in the International System of Units (SI), and therefore one yottabyte is one septillion (one long scale quadrillion) bytes. The unit symbol for the yottabyte is YB.

1 YB = 10008bytes = 1024bytes = 1000000000000000000000000bytes = 1000zettabytes = 1trillionterabytesA related unit, the yobibyte (YiB), using a binary prefix, is equal to 10248bytes (approximately 1.209 YB).

Base unit
Platform-dependent units
Platform-independent units
Traditional bit units
Traditional byte units
IEC bit units
IEC byte units

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