The problem is that Kilo (and Mega, and Giga) indicate a base-10, not a base-2 product. Remember, Kilo is an SI unit prefix which is based on multiples of 10. IEC (later adopted by ISO and IEEE) published a standard to fix this so that Kilo would indicate a base-10 number and Kibi would indicate a base-2 number. The prefixes are: Kibi, Mebi, Gibi, etc. So a 250 Megabyte drive = 232 Mebibytes (MiB).

Of course, no one uses the standard. Drive makers like using the larger numbers, and software makers are just lazy.

So, in a nutshell, computer scientists misuse the SI unit prefixes and confusion ensues.

The whole mess is documented here: http://www.cofc.edu/~frysingj/binprefixes.html

ISO published standard is here: http://www.gscassociates.com/wg8/edcs/text/unit.html

Last edited: Jun 12, 2005