Memory Sizes
Binary prefixes (also known as IEC prefixes) are prefixes for units of measurement that denote multiples of specific powers of two. They are primarily used with units such as bit or byte to measure amounts of data, since powers of two frequently occur in these contexts for technical reasons.
In contrast, decimal prefixes are unit prefixes that denote multiples of specific powers of ten. SI prefixes are decimal prefixes for use in the SI system of units; IEC binary prefixes are binary prefixes intended for use with data quantities. Both the name and the corresponding symbol are referred to as unit prefixes.
Binary prefixes (IEC prefixes)
To avoid ambiguity, the International Electrotechnical Commission (IEC) proposed a new draft standard for binary prefixes in June 1996, which were to be used only in the binary sense. This draft was adopted as a standard in December 1998 and published in January 1999 as an amendment to IEC 60027-2. It introduced the prefixes kibi, mebi, gibi, tebi, pebi, and exbi for binary multiples of units.
| Name | Symbol | Number of Bytes |
|---|---|---|
| Kibibyte | KiB | 1,024 = 2^10 |
| Mebibyte | MiB | 1,048,576 = 2^20 |
| Gibibyte | GiB | 1,073,741,824 = 2^30 |
| Tebibyte | TiB | 1,099,511,627,776 = 2^40 |
| Pebibyte | PiB | 1,125,899,906,842,624 = 2^50 |
| Exbibyte | EiB | 1,152,921,504,606,846,976 = 2^60 |
| Zebibyte | ZiB | 1,180,591,620,717,411,303,424 = 2^70 |
| Yobibyte | YiB | 1,208,925,819,614,629,174,706,176 = 2^80 |
1,024 bytes equals 1 KiB, according to the IEC prefix
Decimal prefixes (SI prefixes)
For data storage devices with binary addressing, storage capacities are technically based on powers of two (2^n bytes). Since there were no specific unit prefixes for powers of two until 1996, it was common practice to use the SI prefixes—which are actually decimal—in the context of storage capacities to denote powers of two (with a factor of 2^10 = 1,024 instead of 1,000). Today, the prefixes should only be used in conjunction with the decimal specification of storage sizes.
| Name | Symbol | Number of Bytes |
|---|---|---|
| Kilobyte | kB | 1,000 = 10^3 |
| Megabyte | MB | 1,000,000 = 10^6 |
| Gigabyte | GB | 1,000,000,000 = 10^9 |
| Terabyte | TB | 1,000,000,000,000 = 10^12 |
| Petabyte | PB | 1,000,000,000,000,000 = 10^15 |
| Exabyte | EB | 1,000,000,000,000,000,000 = 10^18 |
| Zettabyte | ZB | 1,000,000,000,000,000,000,000 = 10^21 |
| Yottabyte | YB | 1,000,000,000,000,000,000,000,000 = 10^24 |
1,000 bytes equals 1 kB, according to the decimal prefix system
You can also find more information on storage sizes in the Wikipedia article “Byte”.