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NAME

       units, kilo, kibi, mega, mebi, giga, gibi - decimal and binary prefixes

DESCRIPTION

   Decimal prefixes
       The  SI  system  of units uses prefixes that indicate powers of ten.  A
       kilometer is 1000 meter, and a megawatt is  1000000  watt.   Below  the
       standard prefixes.

              Prefix   Name    Value
              y        yocto   10^-24 = 0.000000000000000000000001
              z        zepto   10^-21 = 0.000000000000000000001
              a        atto    10^-18 = 0.000000000000000001
              f        femto   10^-15 = 0.000000000000001
              p        pico    10^-12 = 0.000000000001
              n        nano    10^-9  = 0.000000001
              u        micro   10^-6  = 0.000001
              m        milli   10^-3  = 0.001
              c        centi   10^-2  = 0.01
              d        deci    10^-1  = 0.1
              da       deka    10^ 1  = 10
              h        hecto   10^ 2  = 100
              k        kilo    10^ 3  = 1000
              M        mega    10^ 6  = 1000000
              G        giga    10^ 9  = 1000000000
              T        tera    10^12  = 1000000000000
              P        peta    10^15  = 1000000000000000
              E        exa     10^18  = 1000000000000000000
              Z        zetta   10^21  = 1000000000000000000000
              Y        yotta   10^24  = 1000000000000000000000000

       The  symbol  for  micro  is  the Greek letter mu, often written u in an
       ASCII context where this Greek letter is not available.  See also

              http://physics.nist.gov/cuu/Units/prefixes.html

   Binary prefixes
       The binary prefixes resemble the decimal ones, but have  an  additional
       'i'  (and  "Ki"  starts  with  a capital 'K').  The names are formed by
       taking the first syllable of the  names  of  the  decimal  prefix  with
       roughly the same size, followed by "bi" for "binary".

              Prefix   Name   Value
              Ki       kibi   2^10 = 1024
              Mi       mebi   2^20 = 1048576
              Gi       gibi   2^30 = 1073741824
              Ti       tebi   2^40 = 1099511627776
              Pi       pebi   2^50 = 1125899906842624
              Ei       exbi   2^60 = 1152921504606846976

       See also

              http://physics.nist.gov/cuu/Units/binary.html

   Discussion
       Before  these  binary prefixes were introduced, it was fairly common to
       use k=1000 and K=1024, just like b=bit, B=byte.  Unfortunately,  the  M
       is capital already, and cannot be capitalized to indicate binary-ness.

       At  first  that  didn't matter too much, since memory modules and disks
       came in sizes that were powers of two, so everyone knew  that  in  such
       contexts  "kilobyte"  and  "megabyte"  meant  1024  and  1048576 bytes,
       respectively.  What originally was a sloppy use of the prefixes  "kilo"
       and  "mega"  started to become regarded as the "real true meaning" when
       computers were involved.  But then disk technology  changed,  and  disk
       sizes became arbitrary numbers.  After a period of uncertainty all disk
       manufacturers settled on the standard, namely k=1000, M=1000k, G=1000M.

       The situation was messy: in the 14k4  modems,  k=1000;  in  the  1.44MB
       diskettes,  M=1024000; etc.  In 1998 the IEC approved the standard that
       defines the binary prefixes given above, enabling people to be  precise
       and unambiguous.

       Thus, today, MB = 1000000B and MiB = 1048576B.

       In  the  free  software  world  programs  are  slowly  being changed to
       conform.  When the Linux kernel boots and says

              hda: 120064896 sectors (61473 MB) w/2048KiB Cache

       the MB are megabytes and the KiB are kibibytes.

COLOPHON

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