They should not be used to indicate powers of 2 (for example, one kilobit represents 1000 bits and not 1024 bits). These SI prefixes refer strictly to powers of 10. On page 23 of the 7 th edition of the SI brochure, published in 1998, there is a marginal note that, referring to the decimal prefixes, says: There was the need of a different set of binary prefixes to resolve this ambiguity. Moreover, these decimal prefixes are sometimes used with their original meaning even in computing. About 40 years ago, when they started to use this notation, they all knew that the term kilobyte was intended as 1024 bytes and there was no confusion, but when laymen and other specialists (such as scientists and engineers) started to use computers, they weren't aware of this difference. In computing, the units bit and byte are often expressed using powers of 2 and the small difference between 1024 (2¹⁰) and 1000 (10³) led the IT specialists to adopt the use of kilo- to mean 1024. Sometimes "K" is used to indicate ×1024 (2¹⁰) and "k" ×1000 (10³) but this hasn't been standardized and also it can't be extended to the other units, thus the "K" should never be used as a prefix. Even though it's unlikely that the "K" used as kelvin and the "K" improperly used as kilo- might be confused, the latter is wrong. In SI the "K" symbol represent the kelvin, a unit of temperature. (for instance, a nanometer is equal to 0.000000001 metres or 1 m × 10⁻⁹ and its symbol is "nm") but since they are not often used in computing we won't discuss about them.Īll the prefixes shown in the previous table are written in the upper-case form except the "k". To denote the submultiples of the units of measure, there are also other SI prefixes with a negative power of 10, such as milli-, micro-, nano-, etc. ![]() ** Note that only the "kilo-" prefix has a lowercase symbol ('k'). Kilo- means ×1000 or ×10³ and its symbol is "k" (lower-case letter 'k'), thus a km is equal to 1000 metres (or 1 m × 10³).Įvery decimal prefix denotes a specific power of 10 and has a name and a symbol, as shown in the following table: The SI prefixes* * Only the prefixes that denote positive powers of 10 are listed in this table. The International System of Units (abbreviated SI) defines a set of prefixes, with an associated symbol, to represent multiples (or submultiples) of a unit of measure.įor example, the kilo- prefix can be combined with the unit metre to form "kilometre". Differences between Decimal and Binary Prefixes.Binary Prefixes - The IEEE 1541 standard.This article explains what decimal and binary prefixes are, when they should be used, what are the differences between them and how they are used with hardware and software.
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