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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