Kilobyte

The kilobyte (symbol: kB) is a multiple of the unit byte for digital information. Although the prefix kilo- means 1000, the term kilobyte and symbol kB have historically been used to refer to either 1024 (210) bytes or 1000 (103) bytes, dependent upon context, in the fields of computer science and information technology.

For example:

• The HP 21MX real-time computer (1974) denoted 196,608 (which is 192×1024) as "196K", while the HP 3000 business computer (1973) denoted 131,072 (which is 128×1024) as "128K".
• The Shugart SA-400 51⁄₄-inch floppy disk (1976) held 109,375 bytes unformatted, and was advertised as "110 Kbyte", using the 1000 convention. Likewise, the 8-inch DEC RX01 floppy (1975) held 256,256 bytes formatted, and was advertised as "256k". On the other hand, the Tandon 51⁄₄-inch DD floppy format (1978) held 368,640 bytes, but was advertised as "360 KB", following the 1024 convention.
• On modern systems, Mac OS X Snow Leopard represents a 65,536 byte file as "66 KB", rounding to the nearest 1000, while Microsoft Windows 7 would divide by 1024 and represent this as "64 KB".

In December 1998, the IEC addressed such multiple usages and definitions by creating unique binary prefixes to denote multiples of 1024, such as “kibibyte (KiB)”, which represents 210, or 1024, bytes. However, adoption by the computer industry has not been universal, particularly when communicating in a public context, such as to consumers of computer or computer based products.