megabyte

A megabyte or Mbyte is a unit of information or computer storage equal to either 10⁶ (1,000,000) bytes or 2²⁰ (1,048,576) bytes, depending on context. In rare cases, it is used to mean 1000×1024 (1,024,000) bytes. It is commonly abbreviated as Mbyte or MB (not to be confused with Mb, which is used for the megabit). The term megabyte was coined in 1970.^[1]

Definition

The term "megabyte" is ambiguous because it is commonly used to mean either 1000² bytes or 1024² bytes. The confusion originated as compromise technical jargon for the byte multiples that needed to be expressed by the powers of 2 but lacked convenient naming. As 1024 (2¹º) is roughly equal to 1000 (10³), roughly corresponding SI multiples began to be used as approximate binary multiples. In the past few years, standards and government authorities including IEC, IEEE, EU, and NIST, have addressed this ambiguity by promoting the use of megabyte to describe strictly 1000² bytes and "mebibyte" to describe 1024² bytes. This shift is reflected in an increasing number of software projects, but most file managers still show file sizes as "megabytes" ("MB").

The term remains ambiguous and it can follow any one of the following common definitions:

1. 1,000,000 bytes (1000², 10⁶): This is the definition recommended by SI and IEC. This definition is used in networking contexts and most storage media, particularly hard drives, Flash-based storage, 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.
2. 1,048,576 bytes (1024², 2²⁰): This definition is most commonly used in reference to computer memory, but most software that display file size or drive capacity, including file managers also use this definition. See Consumer confusion (in the "gigabyte" article).
3. 1,024,000 bytes (1000×1024): This is used to describe the formatted capacity of USB flash drives and the "1.44 MB" 3.5 inch HD floppy disk, which actually has a 1440 KiB capacity, that is, 1,440×1,024 bytes, or 1,474,560 bytes.

Megabyte examples

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

• a 1024×1024 pixel bitmap image with 8 bit (1 byte) color depth
• 1 minute of 128 kbit/s MP3 compressed music.
• 5.7 seconds of uncompressed CD audio
• 100 pages of single-spaced 12 point font text in OpenOffice.org
• a typical book volume in text format (500 pages × 2000 characters)

See also

• binary prefix
• kilobyte
• gigabyte
• mebibyte
• megabit
• orders of magnitude (data)

External links

• Historical Notes About The Cost Of Hard Drive Storage Space
• the megabyte (established definition in Networking and Storage industries; from whatis.com)
• International Electrotechnical Commission definitions
• IEC prefixes and symbols for binary multiples

References

1. ^ "Megabyte."Webster's Ninth New Collegiate Dictionary. 9th ed. 1983.

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