UNITS(7)                  (2020-08-13)                   UNITS(7)

     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.
               l l l.  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 mc    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

        Binary prefixes
          The binary prefixes resemble the decimal ones, but have an
          additional aqiaq (and "Ki" starts with a capital aqKaq).  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".
               l l l.  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

        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

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     UNITS(7)                  (2020-08-13)                   UNITS(7)

          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
          This page is part of release 5.10 of the Linux man-pages
          project.  A description of the project, information about
          reporting bugs, and the latest version of this page, can be
          found at https://www.kernel.org/doc/man-pages/.

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