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Интерактивная система просмотра системных руководств (man-ов)

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units (7)
  • units (1) ( Solaris man: Команды и прикладные программы пользовательского уровня )
  • units (1) ( FreeBSD man: Команды и прикладные программы пользовательского уровня )
  • units (1) ( Linux man: Команды и прикладные программы пользовательского уровня )
  • units (7) ( Русские man: Макропакеты и соглашения )
  • >> units (7) ( Linux man: Макропакеты и соглашения )
  •  

    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.
    PrefixNameValue
    yyocto10^-24 = 0.000000000000000000000001
    zzepto10^-21 = 0.000000000000000000001
    aatto10^-18 = 0.000000000000000001
    ffemto10^-15 = 0.000000000000001
    ppico10^-12 = 0.000000000001
    nnano10^-9 = 0.000000001
    umicro10^-6 = 0.000001
    mmilli10^-3 = 0.001
    ccenti10^-2 = 0.01
    ddeci10^-1 = 0.1
    dadeka10^ 1 = 10
    hhecto10^ 2 = 100
    kkilo10^ 3 = 1000
    Mmega10^ 6 = 1000000
    Ggiga10^ 9 = 1000000000
    Ttera10^12 = 1000000000000
    Ppeta10^15 = 1000000000000000
    Eexa10^18 = 1000000000000000000
    Zzetta10^21 = 1000000000000000000000
    Yyotta10^24 = 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 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".
    PrefixNameValue
    Kikibi2^10 = 1024
    Mimebi2^20 = 1048576
    Gigibi2^30 = 1073741824
    Titebi2^40 = 1099511627776
    Pipebi2^50 = 1125899906842624
    Eiexbi2^60 = 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

    This page is part of release 3.14 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


     

    Index

    NAME
    DESCRIPTION
    Decimal prefixes
    Binary prefixes
    Discussion
    COLOPHON


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