| Multiples of bytes | ||||
|---|---|---|---|---|
| SI decimal prefixes | IEC binary prefixes | |||
| Name (Symbol) |
Value | Name (Symbol) |
Value | |
| kilobyte (kB) | 103 | kibibyte (KiB) | 210 = 1.024 × 103 | |
| megabyte (MB) | 106 | mebibyte (MiB) | 220 ≈ 1.049 × 106 | |
| gigabyte (GB) | 109 | gibibyte (GiB) | 230 ≈ 1.074 × 109 | |
| terabyte (TB) | 1012 | tebibyte (TiB) | 240 ≈ 1.100 × 1012 | |
| petabyte (PB) | 1015 | pebibyte (PiB) | 250 ≈ 1.126 × 1015 | |
| exabyte (EB) | 1018 | exbibyte (EiB) | 260 ≈ 1.153 × 1018 | |
| zettabyte (ZB) | 1021 | zebibyte (ZiB) | 270 ≈ 1.181 × 1021 | |
| yottabyte (YB) | 1024 | yobibyte (YiB) | 280 ≈ 1.209 × 1024 | |
| See also: Multiples of bits · Orders of magnitude of data | ||||
The kilobyte (symbol: kB)[1] 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.[2][3][4]
For example, the HP 21MX real-time computer (1974) denoted 196,608 (which is 192×1024) as "196K",[5] while the HP 3000 business computer (1973) denoted 131,072 (which is 128×1024) as "128K".[6]
The Shugart SA-400 5¼-inch floppy drive (1977) held 109,375 bytes unformatted,[7] and was advertised as "110 Kbyte", using the 1000 convention.[8] Likewise, the DEC RX01 (1975) held 256,256 bytes formatted, and was advertised as "256k".[9] On the other hand, the Tandon 5¼-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",[10] while Microsoft Windows 7 would represent this as "64 KB".[11]
In December 1998, the IEC attempted to address these dual definitions of the conventional prefixes by proposing unique binary prefixes and prefix symbols to denote multiples of 1024, such as “kibibyte (KiB)”, which exclusively denotes 210 or 1024 bytes.[12] If the proposal had been widely and consistently adopted, it would have liberated the standard unit prefixes to unambiguously refer only to their strict decimal definitions wherein kilobyte would be understood to represent only 1000 bytes. However, in the over‑13 years that have since elapsed, the proposal has seen little adoption by the computer industry.[13][14][15][16]