The basic unit of data is the binary bit (symbol: bit), which can take on a value of 1 or 0. A byte (B) consists of 8 bits.

According to the International System of Quantities, a kilobyte is 1,000 bytes. The recommended symbol is kB. This usage agrees with the International System of Units, which is the modern form of metric measurement. The same is true of mega- (M), giga- (G) and other prefixes.

Because binary arithmetic is so important in computing, kilobytes were traditionally (and continue to be) taken by some companies and users as 2¹⁰ = 1,024 bytes. This is now more properly referred to as a kibibyte (KiB – note the capital K), where the bi denotes the binary origin of the value. Similarly, we have mebibytes (MiB), gibibytes (GiB) and so on.