NAME

       units - 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
              µ        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=1000 k, G=1000 M.

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

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

       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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       information   about   reporting   bugs,   and   the  latest  version  of  this  page,  can  be  found  at
       https://www.kernel.org/doc/man-pages/.

Linux                                              2020-08-13                                           UNITS(7)