units


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 tak-
       ing 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
       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 con-
       form.  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
       This page is part of release 3.35 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://man7.org/linux/man-pages/.



Linux                             2001-12-22                          UNITS(7)
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