SI and Data Size Units
SI Prefixes
The SI specifies a set of metric prefixes (also called SI prefixes). You are probably aware of the term "kilogram" meaning 1000 grams. In this example "kilo" is the SI prefix to the "unit of measure" which is "gram".
| Prefix | Symbol | 10n | Decimal | Term | |
|---|---|---|---|---|---|
| yotta | Y | 1024 | 1000000000000000000000000 | Quadrillion | |
| zetta | Z | 1021 | 1000000000000000000000 | Trilliard | |
| exa | E | 1018 | 1000000000000000000 | Trillion | |
| peta | P | 1015 | 1000000000000000 | Billiard | |
| tera | T | 1012 | 1000000000000 | Billion | |
| giga | G | 109 | 1000000000 | Milliard | |
| mega | M | 106 | 1000000 | Million | |
| kilo | k | 103 | 1000 | Thousand | |
| hecto | h | 102 | 100 | Hundred | |
| deca | da | 101 | 10 | Ten | |
| 100 | 1 | One | |||
| deci | d | 10−1 | 0.1 | Tenth | |
| centi | c | 10−2 | 0.01 | Hundredth | |
| milli | m | 10−3 | 0.001 | Thousandth | |
| micro | μ | 10−6 | 0.000001 | Millionth | |
| nano | n | 10−9 | 0.000000001 | Milliardth | |
| pico | p | 10−12 | 0.000000000001 | Billionth | |
| femto | f | 10−15 | 0.000000000000001 | Billiardth | |
| atto | a | 10−18 | 0.000000000000000001 | Trillionth | |
| zepto | z | 10−21 | 0.000000000000000000001 | Trilliardth | |
| yocto | y | 10−24 | 0.000000000000000000000001 | Quadrillionth | |
A "byte" is 8 bits. A "kilobyte" is 1000 bytes.
Note: Up until 1999 a kilobyte was the term used to describe 1024 bytes (210 bytes). In 1999 the IEC created the term "kibibyte" to mean 1024 and hence removing the incorrect use of the SI prefix SI when it came to writing Binary lengths.
Data Sizes
| IEC Prefix | Symbol | Value | SI Prefix | Symbol | >1999 | <=1999 |
|---|---|---|---|---|---|---|
| kibibyte | KiB | 210 | kilobyte | kB | 103 | 210 |
| mebibyte | MiB | 220 | megabyte | MB | 106 | 220 |
| gibibyte | GiB | 230 | gigabyte | GB | 109 | 230 |
| tebibyte | TiB | 240 | terabyte | TB | 1012 | 240 |
| pebibyte | PiB | 250 | petabyte | PB | 1015 | 250 |
| exbibyte | EiB | 260 | exabyte | EB | 1018 | 260 |
| zebibyte | ZiB | 270 | zettabyte | ZB | 1021 | 270 |
| yobibyte | YiB | 280 | yottabyte | YB | 1024 | 280 |
One kibibyte is 1024 bytes; no ambiguity now between SI and Binary uses. 1000 bytes is called 1 kilobyte (or 1kB), 1024 bytes is called 1 kibibyte (or 1KiB). Notice how the first 2 characters of the IEC prefix have stayed the same as SI prefixes, but then the characters "bi" have been used to symbolise "binary". An "i" has been added to the symbol to show that it is binary (and the lowercase "k" has been changed to uppercase).
