binary prefixes A set of prefixes for binary powers designed to be used in data processing and data transmission contexts. They were suggested in 1998 by the International Electrotechnical Commission (IEC) as a way of resolving the ambiguity in use of kilo-, mega-, giga-, etc., in computing. In scientific usage, these prefixes indicate 10³, 10⁶, 10⁹, etc. (see SI units). In computing, it became common to use the prefix “kilo-” to mean 2¹⁰, so one kilobit was 1024 bits (not 1000 bits). This was extended to larger prefixes, so “mega-” in computing is taken to be 2²⁰ (1 048 576) rather than 10⁶ (1 000 000). However, there is a variation in usage depending on the context. In discussing memory capacities megabyte generally means 2²⁰ bytes, but in disk storage (and data transmission) megabyte is often taken to mean 10⁶ bytes. (In some contexts, as in the capacity of a floppy disk, it has even been quoted as 1 024 000 bytes, i.e. 1000 times a (binary) kilobyte.) The IEC attempted to resolve this confusion by introducing binary prefixes, modeled on the normal decimal prefixes, as follows: kibi- 2¹⁰ mebi- 2²⁰ gebi- 2³⁰ tebi- 2⁴⁰ pebi- 2⁵⁰ exbi- 2⁶⁰ These names are contractions of “kilobinary”, “megabinary”, etc., but are pronounced so that the second syllable rhymes with “bee”. Using these prefixes, one gebibyte would be 1 073 741 824 bytes and one gigabyte would (unambiguously) be 1 000 000 000 bytes. At the present time (2004) these prefixes are not widely used. The IEEE has suggested that the normal SI prefixes (kilo-, mega-, etc.) should be used with their standard meanings unless an explicit explanation of the meaning is given.