Megabyte

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

Quantities of bytes
Popular use and (SI standard meaning)			Binary prefix standards from IEC 60027-2
Name	Symbol	Quantity	Name	Symbol	Quantity
kilobyte	kB	2¹⁰ (10³)	kibibyte	KiB	2¹⁰
megabyte	MB	2²⁰ (10⁶)	mebibyte	MiB	2²⁰
gigabyte	GB	2³⁰ (10⁹)	gibibyte	GiB	2³⁰
terabyte	TB	2⁴⁰ (10¹²)	tebibyte	TiB	2⁴⁰
petabyte	PB	2⁵⁰ (10¹⁵)	pebibyte	PiB	2⁵⁰
exabyte	EB	2⁶⁰ (10¹⁸)	exbibyte	EiB	2⁶⁰
zettabyte	ZB	2⁷⁰ (10²¹)	zebibyte	ZiB	2⁷⁰
yottabyte	YB	2⁸⁰ (10²⁴)	yobibyte	YiB	2⁸⁰

A megabyte is a unit of information or computer storage equal to approximately one million bytes. Megabyte is commonly abbreviated as MB. Mb is used for megabits.

Definition

Because of inconsistencies in the use of SI-derived prefixes such as kilo- and mega-, the exact number can be any one of the following:

1,048,576 bytes (1,024², 2²⁰): This definition is used for nearly all discussions of computer memory (as computer addresses are naturally powers of two, making it efficient to manufacture memory in power-of-two capacities) and file storage. As of 2005, most software uses this definition to express storage capacity (e.g. file size).
1,000,000 bytes (1,000², 10⁶): This is the definition recommended by SI and IEC. It is used primarily in networking contexts and most storage media, particularly hard drives and DVDs. This definition of 'mega-' as a SI prefix is consistent with the other SI prefixes, and with many other uses of the prefix in computing, such as CPU clock speeds or measures of performance.
1,024,000 bytes (1,024×1,000): This definition occurs rarely. It was used in a small number of storage contexts, most notably the "1.44 MB" (actually 1,474,560 bytes), and the "3.5-inch" (actually 90 mm) high-density floppy diskette.

Several attempts to resolve these inconsistencies have been proposed, most notably the standard created by the IEC to redefine 1,048,576 bytes as a "mebibyte". This standard has been adopted by several organizations, such as the NIST and IEEE. See Binary prefix for more information.

Megabytes in use

Usually, the storage capacities of hardware devices such as hard drives are given as 1 megabyte = 1,000,000 bytes (especially for items made in Japan, as Japan has standardized on the metric definition). Other capacities, such as for the RAM capacity of most personal computers, are given as 1 megabyte = 1,048,576 bytes (known unambiguously as a "mebibyte").

Depending on compression methods and file format, a megabyte of data can roughly hold:

one larger book (excluding images),
one "typical" sized photograph with reasonably good quality
a hundred small images, or
roughly a minute of compressed music.

A digital photograph produced by a typical digital camera in 2005 might be 1–4 MB depending on the camera's image resolution and level of compression used.

Until the introduction of hard drives with a capacity of one gigabyte or more, the capacity of hard drives was measured in megabytes.

Megabyte

Definition

Megabytes in use

See also