Kilobyte
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| SI prefixes | Binary prefixes (IEC 60027-2) |
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| Name (Symbol) |
Popular Usage |
Standard SI |
Name (Symbol) |
Value |
| kilobyte (kB) | 210 | 103 | kibibyte (KiB) | 210 |
| megabyte (MB) | 220 | 106 | mebibyte (MiB) | 220 |
| gigabyte (GB) | 230 | 109 | gibibyte (GiB) | 230 |
| terabyte (TB) | 240 | 1012 | tebibyte (TiB) | 240 |
| petabyte (PB) | 250 | 1015 | pebibyte (PiB) | 250 |
| exabyte (EB) | 260 | 1018 | exbibyte (EiB) | 260 |
| zettabyte (ZB) | 270 | 1021 | zebibyte (ZiB) | 270 |
| yottabyte (YB) | 280 | 1024 | yobibyte (YiB) | 280 |
A kilobyte (derived from the SI prefix kilo-, meaning 1000) is a unit of information or computer storage equal to either 1024 or 1000 bytes. It is commonly abbreviated KB, kB, Kbyte or kbyte.
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. As computers became more widely used, this misuse (according to the BIPM) of the SI prefix spread from the slang of computer professionals into the mainstream lexicon, creating much confusion. See binary prefix for more details.
Some have suggested that the capitalized prefix K should be used to distinguish this quantity from the SI prefix k, and although this has never been formally mandated, it is commonly practised (even though K is already used as the SI symbol for kelvins). However, it is not extensible to the higher-order prefixes, as SI already uses the prefixes m and M to mean "thousandth" and "million" respectively. There are also proposals to capitalize all greater-than-unity prefixes (D, H, K, M, G, ...), which would conflict with this. See SI prefix.
These prefixes can therefore be used with either decimal (powers of 1000) or binary (powers of 1024) values, depending on context:
- 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. This definition has been expressly forbidden by the SI standard ([1] section 3.1, marginal note), and most standards organizations instead recommend the term kibibyte (KiB). Although the word "kibibyte" 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. [2]
- 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, with the abbreviation "kB". The overwhelming popularity of the 1024 definition means that anyone using "kilobyte" to mean 1000 in these situations is likely to cause confusion. However, it is common to use 1000 when deriving kilobyte measures from quantities which are not based on powers of two, such as bitrates.
Compare with kilobit, which is more frequently used with the decimal meaning.
