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).[1] Therefore, one megabyte is one million bytes of information. This definition has been incorporated into the
International System of Quantities.
In the computer and information technology fields, other definitions have been used that arose for historical reasons of convenience. A common usage has been to designate one megabyte as 1048576bytes (220 B), a quantity that conveniently expresses the binary architecture of digital computer memory. The standards bodies have deprecated this usage of the megabyte in favor of a new set of
binary prefixes,[2] in which this quantity is designated by the unit
mebibyte (MiB).
Definitions
The unit megabyte is commonly used for 10002 (one million) bytes or 10242 bytes. The interpretation of using base 1024 originated as technical jargon for the byte
multiples that needed to be expressed by the powers of 2 but lacked a convenient name. As 1024 (210) approximates 1000 (103), roughly corresponding to the SI prefix
kilo-, it was a convenient term to denote the binary multiple. In 1999, the
International Electrotechnical Commission (IEC) published standards for
binary prefixes requiring the use of megabyte to denote 10002 bytes, and mebibyte to denote 10242 bytes. By the end of 2009, the IEC Standard had been adopted by the
IEEE,
EU,
ISO and
NIST. Nevertheless, the term megabyte continues to be widely used with different meanings.
1 MB = 1048576 bytes (= 10242 B = 220 B) is the definition used by
Microsoft Windows in reference to
computer memory, such as
random-access memory (RAM). This definition is synonymous with the unambiguous binary unit
mebibyte. In this convention, one thousand and twenty-four megabytes (1024 MB) is equal to one gigabyte (1 GB), where 1 GB is 10243 bytes (i.e., 1
GiB).
Mixed
1 MB = 1024000 bytes (= 1000×1024 B) is the definition used to describe the formatted capacity of the 1.44 MB 3.5-inch HD
floppy disk, which actually has a capacity of 1474560bytes.[5]
Randomly addressable semiconductor memory doubles in size for each address lane added to an integrated circuit package, which favors counts that are powers of two. The capacity of a disk drive is the product of the sector size, number of sectors per track, number of tracks per side, and the number of disk platters in the drive. Changes in any of these factors would not usually double the size.
Examples of use
Depending on compression methods and
file format, a megabyte of data can roughly be: