Memory sizes

Binary prefixes (also IEC prefixes) are prefixes for units of measurement that denote multiples of certain powers of two. They are mainly used with units such as 'bit' or 'byte' to measure data quantities, as powers of two often occur here for technical reasons.

In contrast, decimal prefixes are unit prefixes that denote multiples of certain 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 sets. Both the name and the associated symbol are referred to as unit prefixes.

Binary prefixes (IEC prefixes)

In order to avoid ambiguities, the International Electrotechnical Commission (IEC) proposed a new draft standard for binary prefixes in June 1996, which should only be used in the binary meaning. This draft was adopted as a standard in December 1998 and published as a supplement to IEC 60027-2 in January 1999. 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 byte corresponds to 1 KiB, according to IEC prefix

Decimal prefixes (SI prefixes)

For data memories with binary addressing, storage capacities are technically based on powers of two (2n bytes). As there were no special unit prefixes for powers of two until 1996, it was common to use the actual decimal SI prefixes in connection with storage capacities to designate powers of two (with a factor of 2^10 = 1,024 instead of 1,000). Nowadays, the prefixes should only be used in connection with the decimal specification of memory 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 1,000,000,000,000,000,000,000 = 10^18
Zettabyte ZB 1,000,000,000,000,000,000,000,000 = 10^21
Yottabyte YB 1,000,000,000,000,000,000,000,000,000,000 = 10^24

1,000 byte corresponds to 1 kB, according to decimal prefix

You can also find more information on memory sizes in the Wikipedia article "Byte".

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