Megabyte

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Multiples of bytes
Decimal
ValueMetric
1000kBkilobyte
10002MBmegabyte
10003GBgigabyte
10004TBterabyte
10005PBpetabyte
10006EBexabyte
10007ZBzettabyte
10008YByottabyte
Binary
ValueJEDECIEC
1024KBkilobyteKiBkibibyte
10242MBmegabyteMiBmebibyte
10243GBgigabyteGiBgibibyte
10244--TiBtebibyte
10245--PiBpebibyte
10246--EiBexbibyte
10247--ZiBzebibyte
10248--YiByobibyte
Orders of magnitude of data
 
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Multiples of bytes
Decimal
ValueMetric
1000kBkilobyte
10002MBmegabyte
10003GBgigabyte
10004TBterabyte
10005PBpetabyte
10006EBexabyte
10007ZBzettabyte
10008YByottabyte
Binary
ValueJEDECIEC
1024KBkilobyteKiBkibibyte
10242MBmegabyteMiBmebibyte
10243GBgigabyteGiBgibibyte
10244--TiBtebibyte
10245--PiBpebibyte
10246--EiBexbibyte
10247--ZiBzebibyte
10248--YiByobibyte
Orders of magnitude of data

The megabyte (symbol MB, sometimes abbreviated as Mbyte) is a multiple of the unit byte for digital information storage or transmission with three different values depending on context: 1000000 bytes (106, see prefix mega-) generally for computer storage or transmission rates;[1][2] 1048576 bytes (220, 1024 kilobytes or a mebibyte) generally for computer memory;[1][3] and in rare cases 1000×1024 (1024000) bytes.[2]

Definitions[edit]

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 to the SI prefix kilo-, it began to be used for binary multiples as well. In 1998 the International Electrotechnical Commission (IEC) proposed standards for binary prefixes requiring the use of megabyte to strictly 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 = 1000000 bytes (= 10002 B = 106 B) is the definition recommended by the International System of Units (SI) and the International Electrotechnical Commission IEC.[2] This definition is used in networking contexts and most storage media, particularly hard drives, flash-based storage,[4] 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.[5]
Base 2
1 MB = 1048576 bytes (= 10242 B = 220 B) is the definition used by Microsoft Windows in reference to computer memory (e.g. RAM). See Consumer confusion (in the "gigabyte" article). This definition is synonymous with the unambiguous IEC standard name mebibyte.
Mixed
1 MB = 1024000 bytes (= 1000×1024) B is the definition used to describe the formatted capacity of the "1.44 MB" 3.5 inch HD floppy disk, which actually has a capacity of 1474560 bytes.

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. Sector sizes were set as powers of two (most common 512 bytes or 4096 bytes) 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[edit]

1.44 MB floppy disks can store 1,474,560 bytes of data. MB in this context means 1,000×1,024 bytes.

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

The human genome consists of DNA representing 800 MB of data. The parts that differentiate one person from another can be losslessly compressed to 4 MB.[6]

See also[edit]

References[edit]

  1. ^ a b The American Heritage Science Dictionary. Houghton Mifflin Company. 2005. 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. ^ a b c "Definitions of the SI units: The binary prefixes". National Institute of Standards and Technology. 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" 
  3. ^ "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." 
  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. Retrieved 2009-10-16. 
  6. ^ Christley, S. .; Lu, Y. .; Li, C. .; Xie, X. . (2008). "Human genomes as email attachments". Bioinformatics 25 (2): 274–275. doi:10.1093/bioinformatics/btn582. PMID 18996942.  edit

External links[edit]