The new (December 1998)
prefix for 1024. Its
symbol is Ki (with capital K).
It was created to resolve the confusion between 1000 and 1024. The original prefix kilo always means 1000, and its symbol is k (lower-case).
So 1 kB = one kilobyte = 1000 bytes.
And 1 KiB = one kibibyte = 1024 bytes.
Likewise mega is 1 000 000, mebi is 1 048 576. See prefixes for binary multiples for a fuller explanation.