Megabyte

Multiples of bytes
SI decimal prefixes IEC binary prefixes
Name
(Symbol)
Value Name
(Symbol)
Value
kilobyte (kB) 103 kibibyte (KiB) 210 = 1.024 × 103
megabyte (MB) 106 mebibyte (MiB) 220 ≈ 1.049 × 106
gigabyte (GB) 109 gibibyte (GiB) 230 ≈ 1.074 × 109
terabyte (TB) 1012 tebibyte (TiB) 240 ≈ 1.100 × 1012
petabyte (PB) 1015 pebibyte (PiB) 250 ≈ 1.126 × 1015
exabyte (EB) 1018 exbibyte (EiB) 260 ≈ 1.153 × 1018
zettabyte (ZB) 1021 zebibyte (ZiB) 270 ≈ 1.181 × 1021
yottabyte (YB) 1024 yobibyte (YiB) 280 ≈ 1.209 × 1024
See also: Multiples of bits · Orders of magnitude of data

The megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: 1048576 bytes (220) generally for computer memory;[1][2] and one million bytes (106, see prefix mega-) generally for computer storage.[1][3] The IEEE Standards Board has decided that "Mega will mean 1 000 000", with exceptions allowed for the base-two meaning.[3] In rare cases, it is used to mean 1000×1024 (1024000) bytes.[3] It is commonly abbreviated as Mbyte or MB (compare Mb, for the megabit).

Contents

Definition

The term "megabyte" is commonly used to mean either 10002 bytes or 10242 bytes. This originated as compromise 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 SI multiples began to be used for binary multiples. By the end of 2007, standards and government authorities including IEC, IEEE, EU, and NIST proposed standards for binary prefixes and requiring the use of megabyte to strictly denote 10002 bytes and mebibyte to denote 10242 bytes. The term remains ambiguous and it can follow any one of the following common definitions:

Semiconductor memory doubles in size for each address line 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. Sector sizes were set as powers of two (256 bytes, 512 bytes and so on) for convenience in processing. It was a natural extension to give the capacity of a disk drive in multiples of the sector size, giving a mix of decimal and binary multiples when expressing total disk capacity.

Examples of use

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

See also

References

  1. ^ a b The American Heritage Science Dictionary. Houghton Mifflin Company. 2005. http://www.thefreedictionary.com/megabyte. Retrieved 2009-12-22. "1. A unit of computer memory or data storage capacity equal to 1,048,576 bytes (1,024 kilobytes or 220) bytes. 2. One million bytes. ... prefix mega- often does not have its standard scientific meaning of 1,000,000 ... rate of one megabit per second is equal to one million bits per second ..." 
  2. ^ "What are bits, bytes, and other units of measure for digital information? - Knowledge Base". Indiana University. "1MB is 1,024 kilobytes, or 1,048,576 (1024x1024) bytes, not one million bytes. ... Many hard drive manufacturers use a decimal number system to define amounts of storage space. As a result, 1MB is defined as one million bytes, 1GB is defined as one billion bytes, and so on." 
  3. ^ a b c d "Definitions of the SI units: The binary prefixes". National Institute of Standards and Technology. http://physics.nist.gov/cuu/Units/binary.html. Retrieved 2009-12-22. "third megabyte of 1 024 000 bytes is the megabyte used to format the familiar 90 mm (3½ inch), "1.44 MB" diskette" 
  4. ^ SanDisk USB Flash Drive "Note: 1 megabyte (MB) = 1 million bytes; 1 gigabyte (GB) = 1 billion bytes."
  5. ^ "How Mac OS X reports drive capacity". Apple Inc. 2009-08-27. http://support.apple.com/kb/TS2419. Retrieved 2009-10-16. 

External links