In the metric world, kilo- means 1000. For example, a kilometer is 1000 meters. But in the programming world, we sometimes say kilobyte but mean 1024 bytes, not 1000 bytes. Well apparently the NIST got into the game to resolve the confusion back in 1998.
http://physics.nist.gov/cuu/Units/binar
They defined the prefix kibi- to mean 1024. So now you can say kibibyte if you mean 1024 bytes. Whew, that's a load off my chest. :-)