In 1998, the IEC decreed to call 1,024 bytes
a kibibyte — a term which is only slowly catching on. During the transition period, the IEEE suggests using a lower-case "k" for the decimal kilo (1,000) and, if properly pointed out, an upper-case "K" for the binary kilo (1,024), thereby taking the historical development into account. This is versus the kilobyte
, where kilo is commonly defined as 1000.
It should be noted that many reject the IEC's binary prefixes (kibi-, mebi-, gibi-, tebi-, pebi-, exbi-) on the basis that they sound really, really dumb.