IEEE 1541-2002

IEEE 1541-2002 is a standard issued in 2002 by the Institute of Electrical and Electronics Engineers (IEEE) concerning the use of prefixes for binary multiples of units of measurement related to digital electronics and computing. IEEE 1541-2021 revises and supersedes IEEE 1541–2002, which is 'inactive'.^[1]

While the International System of Units (SI) defines multiples based on powers of ten (like k = 10³, M = 10⁶, etc.), a different definition is sometimes used in computing, based on powers of two (like k = 2¹⁰, M = 2²⁰, etc.). This is due to binary nature of current computing systems, making powers of two the simplest to calculate.

In the early years of computing, there was no significant error in using the same prefix for either quantity (2¹⁰ = 1024 and 10³ = 1000 are equal, to two significant figures). Thus, the SI prefixes were borrowed to indicate nearby binary multiples for these computer-related quantities.

Meanwhile, manufacturers of storage devices, such as hard disks, traditionally used the standard decimal meanings of the prefixes, and decimal multiples are used for transmission rates and processor clock speeds as well. As technology improved, all of these measurements and capacities increased. As the binary meaning was extended to higher prefixes, the absolute error between the two meanings increased. This has even resulted in litigation against hard drive manufacturers, because some operating systems report the size using the larger binary interpretation.

Moreover, there is not a consistent use of the symbols to indicate quantities of bits and bytes – the unit symbol "Mb", for instance, has been widely used for both megabytes and megabits. IEEE 1541 sets new recommendations to represent these quantities and unit symbols unambiguously.

After a trial period of two years, in 2005, IEEE 1541-2002 was elevated to a full-use standard by the IEEE Standards Association, and was reaffirmed on 27 March 2008.

IEEE 1541 is closely related to Amendment 2 of the international standard IEC 60027-2. Later, the IEC standard was harmonized into the common ISO/IEC 80000-13:2008 – Quantities and units – Part 13: Information science and technology. IEC 80000-13 uses 'bit' as the symbol for bit, as opposed to 'b'.