Themegabyte is a multiple of the unitbyte for digital information. Its recommended unit symbol isMB. The unit prefixmega is a multiplier of1000000 (10⁶) in theInternational System of Units (SI).^[1] Therefore, one megabyte is one million bytes of information. This definition has been incorporated into theInternational 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 as1048576bytes (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 ofbinary prefixes,^[2] by means of which the quantity 2²⁰ B is namedmebibyte (symbol MiB).

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 bytemultiples 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 prefixkilo-, it was a convenient term to denote the binary multiple. In 1999, theInternational Electrotechnical Commission (IEC) published standards forbinary prefixes requiring the use ofmegabyte to denote 1000² bytes, andmebibyte to denote 1024² bytes. By the end of 2009, the IEC Standard had been adopted by theIEEE,EU,ISO andNIST. Nevertheless, the term megabyte continues to be widely used with different meanings.

1 MB =1000000 bytes (= 1000² B = 10⁶ B) is the definition following the rules of theInternational System of Units (SI), and theInternational Electrotechnical Commission (IEC).^[2] This definition is used incomputer networking contexts and moststorage media, particularlyhard drives,flash-based storage,^[3] andDVDs, and is also consistent with the other uses of theSI prefix in computing, such asCPU clock speeds ormeasures of performance. TheMac OS X 10.6 file manager is a notable example of this usage in software. SinceSnow Leopard, file sizes are reported in decimal units.^[4]

In this convention, one thousand megabytes (1000 MB) is equal to one gigabyte (1 GB), where 1 GB is one billion bytes.

1 MB =1048576 bytes (= 1024² B = 2²⁰ B) is the definition used byMicrosoft Windows in reference tocomputer memory, such asrandom-access memory (RAM). This definition is synonymous with the unambiguous binary unitmebibyte. 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).

1 MB =1024000 bytes (= 1000×1024 B) is the definition used to describe the formatted capacity of the 1.44 MB3.5-inch HDfloppy disk, which actually has a capacity of1474560bytes.^[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.

Depending on compression methods andfile format,a megabyte of data can roughly be:

• a 1 megapixelbitmap image (e.g. ~1152 × 864) with 256 colors (8 bits/pixelcolor depth) stored without any compression.
• 6 seconds of44.1 kHz/16 bituncompressed CD audio.
• 1 minute of 128 kbit/sMP3lossy compressed audio.
• a typical English book volume in plain text format (500 pages × 2000 characters per page).

The novelThe Picture of Dorian Gray, byOscar Wilde, hosted onProject Gutenberg as an uncompressed plain text file, is 0.429 MB.Great Expectations is 0.994 MB,^[6] andMoby Dick is 1.192 MB.^[7] Thehuman genome consists of DNA representing 800 MB of data. The parts that differentiate one person from another can be compressed to 4 MB.^[8]

• Timeline of binary prefixes
• Gigabyte § Consumer confusion

• Historical Notes About The Cost Of Hard Drive Storage Space
• the megabyte (established definition in Networking and Storage industries; fromwhatis.com)
• International Electrotechnical Commission definitions
• IEC prefixes and symbols for binary multiplesArchived 2004-06-15 at theWayback Machine