Kilobyte
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| SI prefixes | Binary prefixes | |||
| Name (Symbol) |
Standard SI |
Alternate Use |
Name (Symbol) |
Value |
| kilobyte (kB) | 103 = 10001 | 210 | kibibyte (KiB) | 210 |
| megabyte (MB) | 106 = 10002 | 220 | mebibyte (MiB) | 220 |
| gigabyte (GB) | 109 = 10003 | 230 | gibibyte (GiB) | 230 |
| terabyte (TB) | 1012 = 10004 | 240 | tebibyte (TiB) | 240 |
| petabyte (PB) | 1015 = 10005 | 250 | pebibyte (PiB) | 250 |
| exabyte (EB) | 1018 = 10006 | 260 | exbibyte (EiB) | 260 |
| zettabyte (ZB) | 1021 = 10007 | 270 | zebibyte (ZiB) | 270 |
| yottabyte (YB) | 1024 = 10008 | 280 | yobibyte (YiB) | 280 |
A kilobyte (derived from the SI prefix kilo-, meaning 1,000) is a unit of information or computer storage equal to either 1,000 bytes or 1,024 bytes (210), depending on context. It is commonly abbreviated KB, kB, Kbyte or kbyte.
[edit] Ambiguity
The exact number of bytes in a kilobyte has traditionally been ambiguous. Locations in electronic memory circuits are identified by bit vectors, so the most cost-beneficial size for a memory circuit uses the full range of address values, or some power of 2. Since 1024 is a power of 2 and is only slightly in excess of 1000, memory chip makers found it convenient to use multiples of 1024 in marketing material, approximating or treating the additional 24 bytes of each group as manufacturing overhead. At the same time, marketing material for products that did not have the same cost-benefit considerations, such as magnetic disks and networking equipment, continued to use strict decimal-based units.
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 chip 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, since 1998, 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 some software, 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.
