mirror of https://github.com/mkerrisk/man-pages
130 lines
4.1 KiB
Groff
130 lines
4.1 KiB
Groff
'\" t
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.\" Copyright (C) 2001 Andries Brouwer <aeb@cwi.nl>
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" %%%LICENSE_END
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.\"
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.TH UNITS 7 2012-08-05 "Linux" "Linux Programmer's Manual"
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.SH NAME
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units, kilo, kibi, mega, mebi, giga, gibi \- decimal and binary prefixes
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.SH DESCRIPTION
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.SS Decimal prefixes
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The SI system of units uses prefixes that indicate powers of ten.
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A kilometer is 1000 meter, and a megawatt is 1000000 watt.
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Below the standard prefixes.
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.RS
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.TS
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l l l.
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Prefix Name Value
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y yocto 10^-24 = 0.000000000000000000000001
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z zepto 10^-21 = 0.000000000000000000001
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a atto 10^-18 = 0.000000000000000001
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f femto 10^-15 = 0.000000000000001
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p pico 10^-12 = 0.000000000001
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n nano 10^-9 = 0.000000001
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\(mc micro 10^-6 = 0.000001
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m milli 10^-3 = 0.001
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c centi 10^-2 = 0.01
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d deci 10^-1 = 0.1
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da deka 10^ 1 = 10
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h hecto 10^ 2 = 100
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k kilo 10^ 3 = 1000
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M mega 10^ 6 = 1000000
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G giga 10^ 9 = 1000000000
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T tera 10^12 = 1000000000000
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P peta 10^15 = 1000000000000000
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E exa 10^18 = 1000000000000000000
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Z zetta 10^21 = 1000000000000000000000
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Y yotta 10^24 = 1000000000000000000000000
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.TE
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.RE
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The symbol for micro is the Greek letter mu, often written u
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in an ASCII context where this Greek letter is not available.
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See also
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.sp
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.RS
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.UR http://physics.nist.gov\:/cuu\:/Units\:/prefixes.html
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.UE
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.RE
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.SS Binary prefixes
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The binary prefixes resemble the decimal ones,
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but have an additional \(aqi\(aq
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(and "Ki" starts with a capital \(aqK\(aq).
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The names are formed by taking the
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first syllable of the names of the decimal prefix with roughly the same
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size, followed by "bi" for "binary".
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.RS
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.TS
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l l l.
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Prefix Name Value
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Ki kibi 2^10 = 1024
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Mi mebi 2^20 = 1048576
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Gi gibi 2^30 = 1073741824
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Ti tebi 2^40 = 1099511627776
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Pi pebi 2^50 = 1125899906842624
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Ei exbi 2^60 = 1152921504606846976
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.TE
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.RE
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See also
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.sp
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.UR http://physics.nist.gov\:/cuu\:/Units\:/binary.html
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.UE
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.SS Discussion
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Before these binary prefixes were introduced, it was fairly
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common to use k=1000 and K=1024, just like b=bit, B=byte.
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Unfortunately, the M is capital already, and cannot be
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capitalized to indicate binary-ness.
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At first that didn't matter too much, since memory modules
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and disks came in sizes that were powers of two, so everyone
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knew that in such contexts "kilobyte" and "megabyte" meant
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1024 and 1048576 bytes, respectively.
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What originally was a
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sloppy use of the prefixes "kilo" and "mega" started to become
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regarded as the "real true meaning" when computers were involved.
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But then disk technology changed, and disk sizes became arbitrary numbers.
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After a period of uncertainty all disk manufacturers settled on the
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standard, namely k=1000, M=1000k, G=1000M.
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The situation was messy: in the 14k4 modems, k=1000; in the 1.44MB
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.\" also common: 14.4k modem
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diskettes, M=1024000; etc.
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In 1998 the IEC approved the standard
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that defines the binary prefixes given above, enabling people
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to be precise and unambiguous.
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Thus, today, MB = 1000000B and MiB = 1048576B.
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In the free software world programs are slowly
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being changed to conform.
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When the Linux kernel boots and says
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.RS
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.nf
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hda: 120064896 sectors (61473 MB) w/2048KiB Cache
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.fi
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.RE
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the MB are megabytes and the KiB are kibibytes.
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