The megabyte is a multiple of the unit

byte The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable un ...

for digital information. Its recommended unit symbol is MB. The unit prefix ''mega'' is a multiplier of (10⁶) in the

International System of Units The International System of Units, internationally known by the abbreviation SI (from French ), is the modern form of the metric system and the world's most widely used system of measurement. It is the only system of measurement with official s ...

(SI). Therefore, one megabyte is one million bytes of information. This definition has been incorporated into the

International System of Quantities The International System of Quantities (ISQ) is a standard system of Quantity, quantities used in physics and in modern science in general. It includes basic quantities such as length and mass and the relationships between those quantities. This ...

. 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 (2²⁰ B), a quantity that conveniently expresses the binary architecture of digital computer memory. Standards bodies have deprecated this binary usage of the mega- prefix in favor of a new set of binary prefixes, by means of which the quantity 2²⁰ B is named

mebibyte The byte is a units of information, unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character (computing), character of text in a computer and for this ...

(symbol 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- Kilo is a decimal prefix, decimal metric prefix, unit prefix in the metric system denoting multiplication by one thousand (103). It is used in the International System of Units, where it has the symbol k, in Letter case, lowercase. The prefix ' ...

, it was a convenient term to denote the binary multiple. In 1999, the

International Electrotechnical Commission The International Electrotechnical Commission (IEC; ) is an international standards organization that prepares and publishes international standards for all electrical, electronics, electronic and related technologies. IEC standards cover a va ...

(IEC) published standards for binary prefixes requiring the use of ''megabyte'' to denote 1000² bytes, and ''

'' to denote 1024² bytes. By the end of 2009, the IEC Standard had been adopted by the

IEEE The Institute of Electrical and Electronics Engineers (IEEE) is an American 501(c)(3) organization, 501(c)(3) public charity professional organization for electrical engineering, electronics engineering, and other related disciplines. The IEEE ...

, EU,

ISO The International Organization for Standardization (ISO ; ; ) is an independent, non-governmental, international standard development organization composed of representatives from the national standards organizations of member countries. Me ...

and

NIST The National Institute of Standards and Technology (NIST) is an agency of the United States Department of Commerce whose mission is to promote American innovation and industrial competitiveness. NIST's activities are organized into physical s ...

. 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

(SI), and the

(IEC). This definition is used in

computer network A computer network is a collection of communicating computers and other devices, such as printers and smart phones. In order to communicate, the computers and devices must be connected by wired media like copper cables, optical fibers, or b ...

ing contexts and most storage media, particularly

hard drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating hard disk drive platter, pla ...

s, flash-based storage, and DVDs, and is also consistent with the other uses of the

SI prefix The International System of Units, internationally known by the abbreviation SI (from French ), is the modern form of the metric system and the world's most widely used system of measurement. It is the only system of measurement with official st ...

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 Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...

in reference to

computer memory Computer memory stores information, such as data and programs, for immediate use in the computer. The term ''memory'' is often synonymous with the terms ''RAM,'' ''main memory,'' or ''primary storage.'' Archaic synonyms for main memory include ...

, such as

random-access memory Random-access memory (RAM; ) is a form of Computer memory, electronic computer memory that can be read and changed in any order, typically used to store working Data (computing), data and machine code. A random-access memory device allows ...

(RAM). This definition is synonymous with the unambiguous binary unit

. 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 A floppy disk or floppy diskette (casually referred to as a floppy, a diskette, or a disk) is a type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined with a ...

, 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

Depending on compression methods and

file format A file format is a Computer standard, standard way that information is encoded for storage in a computer file. It specifies how bits are used to encode information in a digital storage medium. File formats may be either proprietary format, pr ...

, a megabyte of data can roughly be: * a 1

megapixel In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a Raster graphics, raster image, or the smallest addressable element in a dot matrix display device. In most digital display devices, p ...

bitmap image (e.g. ~ 1152 × 864) with 256 colors (8 bits/pixel color depth) stored without any compression. * 6seconds of 44.1 kHz/16 bit uncompressed CD audio. * 1minute of 128 kbit/s MP3 lossy compressed audio. * a typical English book volume in plain text format (500 pages × 2000 characters per page). The novel ''

The Picture of Dorian Gray ''The Picture of Dorian Gray'' is an 1890 philosophical fiction and Gothic fiction, Gothic horror fiction, horror novel by Irish writer Oscar Wilde. A shorter novella-length version was published in the July 1890 issue of the American period ...

'', by

Oscar Wilde Oscar Fingal O'Fflahertie Wills Wilde (16 October 185430 November 1900) was an Irish author, poet, and playwright. After writing in different literary styles throughout the 1880s, he became one of the most popular and influential playwright ...

, hosted on

Project Gutenberg Project Gutenberg (PG) is a volunteer effort to digitize and archive cultural works, as well as to "encourage the creation and distribution of eBooks." It was founded in 1971 by American writer Michael S. Hart and is the oldest digital li ...

as an uncompressed plain text file, is 0.429 MB. '' Great Expectations'' is 0.994 MB, and ''

Moby Dick ''Moby-Dick; or, The Whale'' is an 1851 Epic (genre), epic novel by American writer Herman Melville. The book is centered on the sailor Ishmael (Moby-Dick), Ishmael's narrative of the maniacal quest of Captain Ahab, Ahab, captain of the whaler ...

'' is 1.192 MB. The

human genome The human genome is a complete set of nucleic acid sequences for humans, encoded as the DNA within each of the 23 distinct chromosomes in the cell nucleus. A small DNA molecule is found within individual Mitochondrial DNA, mitochondria. These ar ...

consists of DNA representing 800MB of data. The parts that differentiate one person from another can be compressed to 4MB.

References

External links

Historical Notes About The Cost Of Hard Drive Storage Space

(established definition in Networking and Storage industries; fro

IEC prefixes and symbols for binary multiples
{{Computer Storage Volumes Units of information