Kilobyte

A kilobyte (derived from the SI prefix kilo-) is a unit of information or computer storage equal to either 1024 or 1000 bytes. It is commonly abbreviated KB, kB, Kbyte, kbyte, or very informally, K or k.

Related Topics:
SI prefix - Kilo - Information - Computer storage - Byte

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The term "kilobyte" was first used to refer to a value of 1024 bytes (210), because the binary nature of digital computers lends itself to quantities that are powers of two, and 210 is roughly one thousand. This misuse of the SI prefix kilo- (the multiplication by 1000 prefix) got carried away from the slang of computer professionals into the mainstream lexicon by marketing people, creating a lot of semantics problems.

Related Topics:
Binary - Digital - Computer - Powers of two - Slang - Lexicon - Marketing - Semantics

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Some suggested that the capitalized prefix K should be used to distinguish this quantity from the SI prefix k. However, the K prefix was never formally mandated and is not used consistently. When larger units were needed for millions of bytes or more, this subtle upper-case / lower-case distinction between the SI prefix and this special use in computing was not available. (SI already uses the prefixes m and M to mean "thousandth" and "million" respectively.) These prefixes can therefore be used with either decimal (powers of 1000) or binary (powers of 1024) values, depending on context. See binary prefix for more details.

Related Topics:
Capitalized - Computing - SI - Binary prefix

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• 1024 bytes (2¹⁰): This definition is always used to express memory capacity, and other quantities which are based on powers of two. Most software also uses it to express storage capacity. However, this definition is explicitly forbidden by the SI standard.http://www.bipm.org/utils/en/pdf/si-brochure.pdf#page=23 This quantity is expressed unambiguously as a kibibyte (KiB), and that name is recommended by most standards organizations. Although it is seldom seen in practice, it is starting to be adopted by software in which precision is important, such as BitTorrent or the Linux kernel. http://lwn.net/2002/0103/a/esr-kibi.php3
• 1000 bytes (10³): This definition is consistent with the SI prefix, and is recommended for all uses by international standards organizations such as IEC, IEEE, and ISO. However, the overwhelming popularity of the 1024 definition means that anyone using "kilobyte" to mean 1000 in these situations is likely to cause confusion. Still, it is common to use 1000 when deriving kilobyte measures from quantities which are not based on powers of two, such as clock speeds or bitrates.

Compare with kilobit, which is more frequently used with the decimal meaning.

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