The kilobyte (symbol: kB) is a multiple of the unit byte for digital information. Historically and in common usage, a kilobyte refers to 1024 (210) bytes in most fields of computer science and information technology. However, hard disk drives measure capacity in strict accordance with the rule of the International System of Units unit prefixes (prefixes like kilo- and mega-) that are based on decimal math. In such mass storage contexts, megabyte equals precisely 1,000,000 bytes and gigabyte is precisely 1,000 times greater than a megabyte. This association suggests that kilobyte can also denote 1,000 bytes in the context of mass storage. Thus, kilobyte and its symbol KB can be ambiguous, their exact value (1,024 or 1,000) dependent upon context.