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.
Base 10 : 1 MB = bytes (= 10002 B = 106 B) is the definition following the rules of the
International System of Units (SI), and the
International Electrotechnical Commission (IEC). and
DVDs, and is also consistent with the other uses of the
SI prefix in computing, such as
CPU clock speeds or
measures of performance. The
Mac OS X 10.6 file manager is a notable example of this usage in software. Since
Snow Leopard, file sizes are reported in decimal units. In this convention, one thousand megabytes (1000 MB) is equal to one gigabyte (1 GB), where 1 GB is one billion bytes.
Base 2 : 1 MB = 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 = bytes (= 1000×1024 B) is the definition used to describe the formatted capacity of the 1.44 MB HD
floppy disk, which actually has a capacity of . 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==