Megabyte
Encyclopedia
The megabyte is a multiple of the unit byte
for digital information storage
or transmission with two different values depending on context: bytes (220) generally for computer memory; and one million byte
s (106, see prefix mega-) generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000 000", with exceptions allowed for the base-two meaning. In rare cases, it is used to mean 1000×1024 bytes. It is commonly abbreviated as Mbyte or MB (compare Mb, for the megabit
).
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 prefix
es and requiring the use of megabyte to strictly denote 10002 bytes and mebibyte
to denote 10242 bytes. This is reflected 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 any one of the following common definitions: bytes (10002, 106): This is the definition recommended by the International System of Units (SI
) and the International Electrotechnical Commission IEC
. This definition is used in networking
contexts and most storage media, particularly hard drives, Flash
-based storage, and DVD
s, 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. 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 not been widespread. 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 bytes.
RAM
usage: In modern computer systems, blocks of main working memory (RAM
) invariably come in sizes that are some-power-of-2 bytes, so for this reason, the binary M-means-1024×1024-system will almost always be used when talking about blocks of RAM. Example: "1 MB of RAM" =1×1024×1024 bytes ( bytes)
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.
, a megabyte of data can roughly be:
Byte
The byte is a unit of digital information in computing and telecommunications that most commonly consists of eight bits. Historically, a byte was the number of bits used to encode a single character of text in a computer and for this reason it is the basic addressable element in many computer...
for digital information storage
Computer storage
Computer data storage, often called storage or memory, refers to computer components and recording media that retain digital data. Data storage is one of the core functions and fundamental components of computers....
or transmission with two different values depending on context: bytes (220) generally for computer memory; and one million byte
Byte
The byte is a unit of digital information in computing and telecommunications that most commonly consists of eight bits. Historically, a byte was the number of bits used to encode a single character of text in a computer and for this reason it is the basic addressable element in many computer...
s (106, see prefix mega-) generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000 000", with exceptions allowed for the base-two meaning. In rare cases, it is used to mean 1000×1024 bytes. It is commonly abbreviated as Mbyte or MB (compare Mb, for the megabit
Megabit
The megabit is a multiple of the unit bit for digital information or computer storage. The prefix mega is defined in the International System of Units as a multiplier of 106 , and therefore...
).
Definition
The term "megabyte" is commonly used to mean either 10002 bytes or 10242 bytes. This originated as compromise technical jargon for the byte multiplesSI prefix
The International System of Units specifies a set of unit prefixes known as SI prefixes or metric prefixes. An SI prefix is a name that precedes a basic unit of measure to indicate a decadic multiple or fraction of the unit. Each prefix has a unique symbol that is prepended to the unit symbol...
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
International Electrotechnical Commission
The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...
, IEEE, EU, and NIST proposed standards for binary prefix
Binary prefix
In computing, a binary prefix is a specifier or mnemonic that is prepended to the units of digital information, the bit and the byte, to indicate multiplication by a power of 2...
es and requiring the use of megabyte to strictly denote 10002 bytes and mebibyte
Mebibyte
The mebibyte is a multiple of the unit byte for digital information. The binary prefix mebi means 220, therefore 1 mebibyte is . The unit symbol for the mebibyte is MiB. The unit was established by the International Electrotechnical Commission in 2000 and has been accepted for use by all major...
to denote 10242 bytes. This is reflected 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 any one of the following common definitions: bytes (10002, 106): This is the definition recommended by the International System of Units (SI
International System of Units
The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...
) and the International Electrotechnical Commission IEC
International Electrotechnical Commission
The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...
. This definition is used in networking
Computer network
A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....
contexts and most storage media, particularly hard drives, Flash
Flash memory
Flash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...
-based storage, and DVD
DVD
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....
s, and is also consistent with the other uses of the SI prefix
SI prefix
The International System of Units specifies a set of unit prefixes known as SI prefixes or metric prefixes. An SI prefix is a name that precedes a basic unit of measure to indicate a decadic multiple or fraction of the unit. Each prefix has a unique symbol that is prepended to the unit symbol...
in computing, such as CPU clock speeds or measures of performance
FLOPS
In computing, FLOPS is a measure of a computer's performance, especially in fields of scientific calculations that make heavy use of floating-point calculations, similar to the older, simpler, instructions per second...
. The Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
10.6 file manager is a notable example of this usage in software. Since Snow Leopard, file sizes are reported in decimal units. bytes (10242, 220): This definition is most commonly used in reference to computer memory
Computer memory
In computing, memory refers to the physical devices used to store programs or data on a temporary or permanent basis for use in a computer or other digital electronic device. The term primary memory is used for the information in physical systems which are fast In computing, memory refers to the...
, 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
Mebibyte
The mebibyte is a multiple of the unit byte for digital information. The binary prefix mebi means 220, therefore 1 mebibyte is . The unit symbol for the mebibyte is MiB. The unit was established by the International Electrotechnical Commission in 2000 and has been accepted for use by all major...
, however as of 2011 adoption of the standard has not been widespread. bytes (1000×1024): This is used to describe the formatted capacity of the "1.44 MB" 3.5 inch HD floppy disk
Floppy disk
A floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles...
, which actually has a capacity of bytes.
RAM
Ram
-Animals:*Ram, an uncastrated male sheep*Ram cichlid, a species of freshwater fish endemic to Colombia and Venezuela-Military:*Battering ram*Ramming, a military tactic in which one vehicle runs into another...
usage: In modern computer systems, blocks of main working memory (RAM
Ram
-Animals:*Ram, an uncastrated male sheep*Ram cichlid, a species of freshwater fish endemic to Colombia and Venezuela-Military:*Battering ram*Ramming, a military tactic in which one vehicle runs into another...
) invariably come in sizes that are some-power-of-2 bytes, so for this reason, the binary M-means-1024×1024-system will almost always be used when talking about blocks of RAM. Example: "1 MB of RAM" =1×1024×1024 bytes ( bytes)
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 formatFile format
A file format is a particular way that information is encoded for storage in a computer file.Since a disk drive, or indeed any computer storage, can store only bits, the computer must have some way of converting information to 0s and 1s and vice-versa. There are different kinds of formats for...
, a megabyte of data can roughly be:
- a 1024×1024 pixel bitmapBitmapIn computer graphics, a bitmap or pixmap is a type of memory organization or image file format used to store digital images. The term bitmap comes from the computer programming terminology, meaning just a map of bits, a spatially mapped array of bits. Now, along with pixmap, it commonly refers to...
image with 256 colors (8 bpp color depthColor depthIn computer graphics, color depth or bit depth is the number of bits used to represent the color of a single pixel in a bitmapped image or video frame buffer. This concept is also known as bits per pixel , particularly when specified along with the number of bits used...
). - 1 minute of 128 kbit/s MP3MP3MPEG-1 or MPEG-2 Audio Layer III, more commonly referred to as MP3, is a patented digital audio encoding format using a form of lossy data compression...
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 prefixBinary prefixIn computing, a binary prefix is a specifier or mnemonic that is prepended to the units of digital information, the bit and the byte, to indicate multiplication by a power of 2...
- MegabitMegabitThe megabit is a multiple of the unit bit for digital information or computer storage. The prefix mega is defined in the International System of Units as a multiplier of 106 , and therefore...
- Orders of magnitude (data)Orders of magnitude (data)An order of magnitude is generally a factor of ten. A quantity growing by four orders of magnitude implies it has grown by a factor of 10000 or 104. However, because computers are binary, orders of magnitude are sometimes given as powers of two....
- Timeline of binary prefixesTimeline of binary prefixesThis article presents a terminology timeline of binary prefixes. Early computers used two different approaches to memory addressing, representing the address as either a binary number or as a decimal number. Early machines that used decimal addressing included the ENIAC, UNIVAC 1, IBM 702, IBM 705,...
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