A kilobyte can be defined as either 1024 bytes or 1000 bytes. Similarly, a megabyte could be 1024 kilobytes or 1000 kilobytes, and so forth. Really, 1024 is the number that makes more sense, but hard drive manufacturers promoted the “1000 bytes” interpretation so they could advertise their hard drives as having more megabytes.

Some standards organizations tried to “solve” the issue by defining a “kibibyte” as 1024 bytes and so forth, but you only ever see those in abbreviated forms (ie KiB). I personally hate that convention; the words are aesthetically atrocious and were only invented to please pedants (who annoy me) and dishonest marketing people (whom I detest even more).

Isn't this the difference between speed notation and size notation?