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Prefixes for binary multiples
In December 1998 the International Electrotechnical Commission (IEC), the leading
international organization for worldwide standardization in electrotechnology,
approved as an IEC International Standard names and symbols for prefixes for
binary multiples for use in the fields of data processing and data transmission.
The prefixes are as follows:
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Prefixes for binary multiples
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Factor Name Symbol Origin Derivation
2^10 kibi Ki kilobinary: (2^10)^1 kilo: (10^3)^1
2^20 mebi Mi megabinary: (2^10)^2 mega: (10^3)^2
2^30 gibi Gi gigabinary: (2^10)^3 giga: (10^3)^3
2^40 tebi Ti terabinary: (2^10)^4 tera: (10^3)^4
2^50 pebi Pi petabinary: (2^10)^5 peta: (10^3)^5
2^60 exbi Ei exabinary: (2^10)^6 exa: (10^3)^6
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Examples and comparisons with SI prefixes
one kibibit 1 Kibit = 2^10 bit = 1024 bit
one kilobit 1 kbit = 10^3 bit = 1000 bit
one byte 1 B = 2^3 bit = 8 bit
one mebibyte 1 MiB = 2^20 B = 1 048 576 B
one megabyte 1 MB = 10^6 B = 1 000 000 B
one gibibyte 1 GiB = 2^30 B = 1 073 741 824 B
one gigabyte 1 GB = 10^9 B = 1 000 000 000 B
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It is suggested that in English, the first syllable of the name of the
binary-multiple prefix should be pronounced in the same way as the first syllable
of the name of the corresponding SI prefix, and that the second syllable should
be pronounced as "bee".
It is important to recognize that the new prefixes for binary multiples are not
part of the International System of Units (SI), the modern metric system.
However, for ease of understanding and recall, they were derived from the SI
prefixes for positive powers of ten. As can be seen from the above table, the
name of each new prefix is derived from the name of the corresponding SI prefix
by retaining the first two letters of the name of the SI prefix and adding the
letters "bi," which recalls the word "binary". Similarly, the symbol of each new
prefix is derived from the symbol of the corresponding SI prefix by adding the
letter "i," which again recalls the word "binary". (For consistency with the
other prefixes for binary multiples, the symbol Ki is used for 2^10 rather than
ki.)
Official publication
These prefixes for binary multiples, which were developed by IEC Technical
Committee (TC) 25, Quantities and units, and their letter symbols, with the
strong support of the International Committee for Weights and Measures (CIPM) and
the Institute of Electrical and Electronics Engineers (IEEE), were first adopted
by the IEC as Amendment 2 to IEC International Standard IEC 60027-2: Letter
symbols to be used in electrical technology - Part 2: Telecommunications and
electronics. The full content of Amendment 2, which has a publication date of
1999-01, is reflected in the tables above and the suggestion regarding
pronunciation. Subsequently the contents of this Amendment were incorportated in
the second edition of IEC 60027-2, which has a publication date of 2000-11 (the
first edition was published in 1972). The complete citation for this revised
standard is IEC 60027-2, Second edition, 2000-11, Letter symbols to be used in
electrical technology - Part 2: Telecommunications and electronics.
Historical context^*
Once upon a time, computer professionals noticed that 2^10 was very nearly equal
to 1000 and started using the SI prefix "kilo" to mean 1024. That worked well
enough for a decade or two because everybody who talked kilobytes knew that the
term implied 1024 bytes. But, almost overnight a much more numerous "everybody"
bought computers, and the trade computer professionals needed to talk to
physicists and engineers and even to ordinary people, most of whom know that a
kilometer is 1000 meters and a kilogram is 1000 grams.
Then data storage for gigabytes, and even terabytes, became practical, and the
storage devices were not constructed on binary trees, which meant that, for many
practical purposes, binary arithmetic was less convenient than decimal
arithmetic. The result is that today "everybody" does not "know" what a megabyte
is. When discussing computer memory, most manufacturers use megabyte to mean
2^20 = 1 048 576 bytes, but the manufacturers of computer storage devices usually
use the term to mean 1 000 000 bytes. Some designers of local area networks have
used megabit per second to mean 1 048 576 bit/s, but all telecommunications
engineers use it to mean 10^6 bit/s. And if two definitions of the megabyte are
not enough, a third megabyte of 1 024 000 bytes is the megabyte used to format
the familiar 90 mm (3 1/2 inch), "1.44 MB" diskette. The confusion is real, as is
the potential for incompatibility in standards and in implemented systems.
Faced with this reality, the IEEE Standards Board decided that IEEE standards
will use the conventional, internationally adopted, definitions of the SI
prefixes. Mega will mean 1 000 000, except that the base-two definition may be
used (if such usage is explicitly pointed out on a case-by-case basis) until such
time that prefixes for binary multiples are adopted by an appropriate standards
body.
Return to [18]SI prefixes
*Historical context adapted from: Bruce Barrow, "A Lesson in Megabytes," IEEE
Standards Bearer, January 1997, page 5. Portions copyright © 1997 by the
Institute of Electrical and Electronics Engineers, Inc. The IEEE disclaims any
responsibility or liability resulting from the placement and use in the described
manner. Information is reprinted with the permission of the IEEE.
References
1. https://physics.nist.gov/cuu/index.html
2. https://physics.nist.gov/cuu/Units/index.html
3. https://physics.nist.gov/cuu/Units/index.html
4. https://physics.nist.gov/cuu/Units/index.html
5. https://physics.nist.gov/cuu/Units/index.html
6. https://physics.nist.gov/cuu/Units/introduction.html
7. https://physics.nist.gov/cuu/Units/units.html
8. https://physics.nist.gov/cuu/Units/prefixes.html
9. https://physics.nist.gov/cuu/Units/outside.html
10. https://physics.nist.gov/cuu/Units/rules.html
11. https://physics.nist.gov/cuu/Units/background.html
12. https://physics.nist.gov/cuu/Units/bibliography.html
13. https://physics.nist.gov/cuu/Units/bibliography.html
14. https://physics.nist.gov/cuu/index.html
15. https://physics.nist.gov/cuu/index.html
16. https://physics.nist.gov/cuu/index.html
17. https://physics.nist.gov/cuu/index.html
18. https://physics.nist.gov/cuu/Units/prefixes.html
Usage: http://www.kk-software.de/kklynxview/get/URL
e.g. http://www.kk-software.de/kklynxview/get/http://www.kk-software.de
Errormessages are in German, sorry ;-)