A
unit prefix is a specifier or mnemonic that is prepended to
units of measurement to indicate multiples or fractions of the units. Units of various
sizes are commonly formed by the use of such
prefixes. The
prefixes of the metric system, such as
kilo and
milli, represent multiplication by
powers of ten. In information technology it is common to use
binary prefixes, which are based on
powers of two. Historically, many prefixes have been used or proposed by various sources, but only a narrow set has been recognised by standards organisations.