Multiples of bytes

SI decimal prefixes Binary

usage

IEC binary prefixes

Name

(Symbol)

Value Name

(Symbol)

Value

kilobyte (kB) 103 210 kibibyte (KiB) 210

megabyte (MB) 106 220 mebibyte (MiB) 220

gigabyte (GB) 109 230 gibibyte (GiB) 230

terabyte (TB) 1012 240 tebibyte (TiB) 240

petabyte (PB) 1015 250 pebibyte (PiB) 250

exabyte (EB) 1018 260 exbibyte (EiB) 260

zettabyte (ZB) 1021 270 zebibyte (ZiB) 270

yottabyte (YB) 1024 280 yobibyte (YiB) 280

See also: Multiples of bits · Orders of magnitude of data

MegabyteFrom Wikipedia, the free encyclopedia

The megabyte is a multiple of the unit byte for digital information storage or transmission with two different

values depending on context: 1 048 576 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 (1 024 000) bytes.[3] It is commonly abbreviated as Mbyte or MB (compare Mb, for themegabit).

Contents

1 Definition2 Examples of use

3 See also4 References

5 External links

Definition

The term "megabyte" is commonly used to mean either

10002 bytes or 10242 bytes. This originated ascompromise technical jargon for the byte multiples thatneeded 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, standardsand 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. This isreflected in an increasing number of software projects using the new definitions, but some file managers still

show file sizes using the binary interpretation (10242 bytes). The term remains ambiguous and it can follow anyone of the following common definitions:

1 000 000 bytes (10002, 106): This is the definition recommended by the International System of

Units (SI) and the International Electrotechnical Commission IEC.[3] 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]

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). This definition is synonymous with the

unambiguous IEC standard name mebibyte, however as of 2011 adoption of the standard has notbeen widespread.

1 024 000 bytes (1000×1024): This is used to describe the formatted capacity of the "1.44 MB"

3.5 inch HD floppy disk, which actually has a capacity of 1 474 560 bytes.

1.44 MB floppy disks can store

1,474,560 bytes of data. MB in

this context means 1,000×1,024

bytes.

RAM usage: In modern computer systems, blocks of main working memory (RAM) invariably come in sizesthat are some-power-of-2 bytes, so for this reason, the binary M-means-1024×1024-system will almost alwaysbe used when talking about blocks of RAM. Example: "1 MB of RAM" =1×1024×1024 bytes (1 048 576bytes)

Semiconductor memory doubles in size for each address line added to an integrated circuit package, whichfavors counts that are powers of two. The capacity of a disk drive is the product of the sector size, number ofsectors per track, number of tracks per side, and the number of disk platters in the drive. Changes in any ofthese factors would not usually double the size. Sector sizes were set as powers of two (256 bytes, 512 bytesand so on) for convenience in processing. It was a natural extension to give the capacity of a disk drive inmultiples 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 datacan roughly be:

a 1024×1024 pixel bitmap image with 256 colors (8 bppcolor depth).

1 minute of 128 kbit/s MP3 compressed music.6 seconds of uncompressed CD audio.

a typical English book volume in plain text format (500 pages× 2000 characters per page).

See also

Binary prefixMegabit

Orders of magnitude (data)Timeline of binary prefixes

References

1. ̂a b The American Heritage Science Dictionary (http://www.thefreedictionary.com/megabyte) . HoughtonMifflin 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. Onemillion bytes. ... prefix mega- often does not have its standard scientific meaning of 1,000,000 ... rate of onemegabit 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". IndianaUniversity. "1MB is 1,024 kilobytes, or 1,048,576 (1024x1024) bytes, not one million bytes. ... Many harddrive manufacturers use a decimal number system to define amounts of storage space. As a result, 1MB isdefined 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" (http://physics.nist.gov/cuu/Units/binary.html) .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), "1.44MB" diskette"

4. ^ SanDisk USB Flash Drive (http://apac.sandisk.com/Products/Catalog(1349)-SanDisk_Extreme_Ducati_Edition_USB_Flash_Drive.aspx) "Note: 1 megabyte (MB) = 1 million bytes; 1gigabyte (GB) = 1 billion bytes."

5. ^ "How Mac OS X reports drive capacity" (http://support.apple.com/kb/TS2419) . Apple Inc. 2009-08-27.http://support.apple.com/kb/TS2419. Retrieved 2009-10-16.

External links

Historical Notes About The Cost Of Hard Drive Storage Space(http://www.alts.net/ns1625/winchest.html)

the megabyte (http://searchstorage.techtarget.com/sDefinition/0,,sid5_gci212542,00.html)(established definition in Networking and Storage industries; from whatis.com

(http://whatis.techtarget.com/definition/0,,sid9_gci551931,00.html) )International Electrotechnical Commission definitions (http://www.iec.ch/zone/si/si_bytes.htm)IEC prefixes and symbols for binary multiples (http://members.optus.net/alexey/prefBin.xhtml)

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Categories: Units of information

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