Megabyte

From Free net encyclopedia

Template:This article is about Template:Quantities of bytes A megabyte is a unit of information or computer storage equal to approximately one million bytes. Megabyte is commonly abbreviated as MB (not to be confused with Mb, which is used for megabits), and sometimes as meg.

1 Definition
2 Megabytes in use
3 Consumer confusion
4 See also
5 External links

[edit]

Definition

Because of inconsistencies in the use of SI-derived prefixes such as kilo- and mega-, the exact number can be any one of the following:

1,048,576 bytes (1,024², 2²⁰): This definition is used for nearly all discussions of computer memory (as computer addresses are naturally powers of two, making it efficient to manufacture memory in power-of-two capacities) and file storage. As of 2005, most software uses this definition to express storage capacity (e.g. file size).
1,000,000 bytes (1,000², 10⁶): This is the definition recommended by IEC. It is used primarily in networking contexts and most storage media, particularly hard drives and DVDs. This definition of 'mega-' as a "binary prefix is consistent with the other SI prefixes, and with many other uses of the prefix in computing, such as CPU clock speeds or measures of performance.
1,024,000 bytes (1,024×1,000): This definition occurs rarely. It was used in a small number of storage contexts, most notably the "1.44 MB" (actually 1,474,560 bytes) "3.5-inch" (actually 90 mm) high-density floppy diskette.

Several attempts to resolve these inconsistencies have been proposed, most notably the standard created by the IEC to redefine 1,048,576 bytes as a "mebibyte". This standard has been adopted by several organizations, such as the NIST and IEEE. See Binary prefix for more information.

[edit]

Megabytes in use

Usually, the storage capacities of hardware devices such as Hard drives are given as 1 megabyte = 1,000,000 bytes (especially for items made in Japan, as Japan has standardized on the metric definition). Other capacities, such as for the RAM capacity of most personal computers, are given as 1 megabyte = 1,048,576 bytes (known unambiguously as a "mebibyte").

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

one larger book (excluding images),
one "typical" sized photograph with reasonably good quality
a hundred small images, or
roughly a minute of compressed music.

A digital photograph produced by a typical digital camera in 2005 might be between 1–4 MB depending on the camera's image resolution and level of compression used.

Until the introduction of hard drives with a capacity of one gigabyte or more, the capacity of hard drives was measured in megabytes.

[edit]

Consumer confusion

Note that computer memory is addressed in base 2, due to its design, so memory size is always a power of two. It is thus convenient to measure in binary units. Other computer measurements, like storage hardware size, data transfer rates, clock speeds, operations per second, and so on do not have an inherent base, and are usually measured in decimal units. Consumers who are (initially) unaware of varying meanings of the abbreviations often feel shortchanged when they discover the difference, and claim that manufacturers of drives and data transfer devices are using the decimal measurements in an intentionally misleading way to inflate their numbers, though these measurements are the norm in all fields other than computer memory and storage.

For instance, if a hard drive is said by a vendor to store 140 GB of data, the disk can store 140Template:E bytes. Generally, operating systems allocate and report disk and files sizes in binary units, and present them using abbreviations (e.g GB, MB, KB) also used by the decimal system, so this drive would be reported as "130 GB" (actually 130.36 GiB). Some have even sued these manufacturers for deceptive advertising, because of the discrepancy. (Furthermore, the drive wouldn't be able to store files with a total filesize of 130.36 GiB, either, due to filesystem overhead. See Partition (computing).)

If the standard IEC prefixes were used universally, this confusion would be eliminated. Template:Details

[edit]