Prefixes for Binary and Decimal Multiples
Binary versus decimal
The International System of Units (SI) prefixes and symbols (e.g., kilo-, Mega-, Giga-) are often used interchangeably (and incorrectly) for decimal and binary values. This misuse not only causes confusion and errors, but the errors compound as the numbers increase. In terms of storage, this can cause significant problems. For example, consider that a kilobyte (103) of data is only 24 bytes less than 210 bytes of data. Although this difference may be of little consequence, the table below demonstrates how the differences increase and become significant.
To alleviate the confusion, the International Electrotechnical Commission (IEC) adopted a standard of prefixes for binary multiples for use in information technology. The table below compares the SI and IEC prefixes, symbols, and values.
| SI decimal vs IEC binary prefixes for multiples | |||||
|---|---|---|---|---|---|
| SI decimal standard | IEC binary standard | ||||
|
Prefix (Symbol) | Power | Value | Value | Power |
Prefix (Symbol) |
| kilo- (kB) | 103 | 1000 | 1024 | 210 | kibi- (KiB) |
| mega- (MB) | 106 | 1000000 | 1048576 | 220 | mebi- (MiB) |
| giga- (GB) | 109 | 1000000000 | 1073741824 | 230 | gibi- (GiB) |
| tera- (TB) | 1012 | 1000000000000 | 1099511627776 | 240 | tebi- (TiB) |
| peta- (PB) | 1015 | 1000000000000000 | 1125899906842624 | 250 | pebi- (PiB) |
| exa- (EB) | 1018 | 1000000000000000000 | 1152921504606846976 | 260 | exbi- (EiB) |
| zetta- (ZB) | 1021 | 1000000000000000000000 | 1180591620717411303424 | 270 | zebi- (ZiB) |
| yotta- (YB) | 1024 | 1000000000000000000000000 | 1208925819614629174706176 | 280 | yobi- (YiB) |
For a detailed explanation, including a historical perspective, see http://physics.nist.gov/cuu/Units/binary.html.