IEEE 1541-2002 - Recommendations

Recommendations

IEEE 1541 recommends:

• a set of units to refer to quantities used in digital electronics and computing:
  • bit (symbol 'b'), a binary digit;
  • byte (symbol 'B'), a set of adjacent bits (usually, but not necessarily, eight) operated on as a group;
  • octet (symbol 'o'), a group of eight bits;
• a set of prefixes to indicate binary multiples of the aforesaid units:
  • kibi (symbol 'Ki'), 210 = 1024;
  • mebi (symbol 'Mi'), 220 = 1048576;
  • gibi (symbol 'Gi'), 230 = 1073741824;
  • tebi (symbol 'Ti'), 240 = 1099511627776;
  • pebi (symbol 'Pi'), 250 = 1125899906842624;
  • exbi (symbol 'Ei'), 260 = 1152921504606846976;
• that the first part of the binary prefix is pronounced as the analogous SI prefix, and the second part is pronounced as bee;
• that SI prefixes are not used to indicate binary multiples.

The bi part of the prefix comes from the word binary, so for example, kibibyte means a kilobinary byte, that is 1024 bytes.

Note the capital 'K' for the kibi- symbol: while the symbol for the analogous SI prefix kilo- is a small 'k', a capital 'K' has been selected for consistency with the other prefixes and with the widespread use of the misspelled SI prefix (as in 'KB').

IEEE 1541 is closely related to Amendment 2 to IEC International Standard IEC 60027-2, except the latter uses 'bit' as the symbol for bit, as opposed to 'b'.

Today, the harmonized ISO/IEC IEC 80000-13:2008 - Quantities and units -- Part 13: Information science and technology standard cancels and replaces subclauses 3.8 and 3.9 of IEC 60027-2:2005 (those related to Information theory and Prefixes for binary multiples).