Telecommunications engineers and storage manufacturers define the kilobyte as 1000 bytes, based on the SI prefix. This is also what most people (before exposure to computers) think a kilobyte is. This leads to some confusion when the novice purchases computer equipment, as the computer will report a smaller amount than the manufacturer stated.
The International Electrotechnical Commission has defined the kilobyte as 1000 bytes, and have 1024 bytes called a kibibyte (KiB) -- a term which very few have adopted.
See integral data type, megabyte, gigabyte.