SI Prefix

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What Does SI Prefix Mean?

The SI prefixes are a series of prefixes to units in the International System of Units, or SI. These can denote very small or very large amounts. They are most commonly used in computing to refer to storage space, such as bytes, even though storage is not an official SI unit.


Techopedia Explains SI Prefix

SI prefixes denote the amounts of SI units, commonly known as the metric system. They are based on powers of ten.

  • yotta: 1024
  • zetta: 1021
  • exa: 1018
  • peta: 1015
  • tera: 1012
  • giga: 109
  • mega: 106
  • kilo: 103
  • hecto: 102
  • deci: 10-1
  • centi: 10-2
  • milli: 10-3
  • micro: 10-6
  • nano: 10-9
  • pico: 10-12
  • femto: 10-15
  • atto: 10-18
  • zepto: 10-21
  • yocto: 10-24

The mega, giga and kilo prefixes are familiar to many people even in countries where imperial measurements are more common, such as the U.S., thanks to their usage for measuring computer storage. For example, one gigabyte is 1,000 bytes. These prefixes also have other usages in computing. Since the components on hardware circuit boards are so small, they are usually measured in micrometers or microns.


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Margaret Rouse
Technology Expert
Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.