This article is about a unit of data measurement. For the cartoon character, see ReBoot.

A megabyte (informally, meg) is a unit of measurement for computer storage, memory and information that is either exactly or approximately equal to one million bytes, depending on the definition used. The most-often used symbol for megabyte is MB, with Mb close behind, although the latter is also used to stand for megabit.

Three definitions are currently in use:

1. 1,048,576 bytes (1024² or 2²⁰): Though unofficial, this is the definition used in almost all cases. One megabyte is 1,024 kilobytes. One gigabyte is 1,024 megabytes. The reason is that computers use the binary numeral system internally. This is also referred to as a mebibyte (MiB or Mib, whose magnitude is not in doubt).
2. 1,000,000 bytes (10⁶): This is a definition used by hard drive manufacturers. It is also consistent with the SI prefix "mega" and is endorsed by international standards bodies.
3. 1,024,000 bytes (1,024×1,000): This is a "definition" used by floppy disk and Flash drive manufacturers.

To reduce the confusion and distinguish between meanings (1) and (2) above, the International Electrotechnical Commission (IEC), adopted an international standard in December 1998 which reserves the term megabyte for 10⁶ bytes and introduces the new prefix mebi (symbol Mi) for 2²⁰. Similarly, the prefixes kibi (Ki, equal to 2¹⁰) and gibi (Gi, equal to 2³⁰) were introduced. This naming convention, strongly endorsed by IEEE and CIPM, is slowly coming into common usage.

Note also the distinction between a megabyte (one million bytes) and a megabit (one million bits). A megabit is abbreviated as Mbit (preferably) or as Mb (when the byte is abbreviated by an upper case "B", which stands for Bel in SI). There are eight bits in one byte, so a megabyte is eight times as large as a megabit. Megabits are often used in applications where a serial bitstream is the item of interest, particularly in communications and in specifying the internal data rate of a computer hard drive. In these contexts, one megabit is almost invariably defined as 10⁶ bits. In practice, when the symbol Mb is encountered, an examination of the context is necessary to indicate which unit of measure was intended.

Similarly, a Gbit is a gigabit and a kbit is a kilobit.

Computer professionals and knowledgeable users often use the abbreviation "meg" in place of the full term, as in "50 megs" for 50 megabytes, though this abbreviation is more often spoken than written.

Unicode has a symbol for Megabyte: (㎆).

See also

• Binary prefix
• Integral data type
• List of device bandwidths
• Octet

External links

• Prefixes for binary multiples (http://www.iec.ch/zone/si/si_bytes.htm). International Electrotechnical Commission.
• Prefixes for binary multiples (http://physics.nist.gov/cuu/Units/binary.html). NIST Reference on Constants, Units, and Uncertainty.
• Michael Quinton. Kibibyte (http://www.worldwidewords.org/turnsofphrase/tp-kib1.htm). (August 21, 1999). World Wide Words.
• Conversion: bits and bytes (http://www.sengpielaudio.com/calculator-bits.htm). Sengpielaudio. (conversion calculator)