2 .\" Copyright (C) 2001 Andries Brouwer <aeb@cwi.nl>
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24 .TH UNITS 7 2001-12-22 "Linux" "Linux Programmer's Manual"
26 units, kilo, kibi, mega, mebi, giga, gibi \- decimal and binary prefixes
29 The SI system of units uses prefixes that indicate powers of ten.
30 A kilometer is 1000 meter, and a megawatt is 1000000 watt.
31 Below the standard prefixes.
36 y yocto 10^-24 = 0.000000000000000000000001
37 z zepto 10^-21 = 0.000000000000000000001
38 a atto 10^-18 = 0.000000000000000001
39 f femto 10^-15 = 0.000000000000001
40 p pico 10^-12 = 0.000000000001
41 n nano 10^-9 = 0.000000001
42 u micro 10^-6 = 0.000001
49 M mega 10^ 6 = 1000000
50 G giga 10^ 9 = 1000000000
51 T tera 10^12 = 1000000000000
52 P peta 10^15 = 1000000000000000
53 E exa 10^18 = 1000000000000000000
54 Z zetta 10^21 = 1000000000000000000000
55 Y yotta 10^24 = 1000000000000000000000000
59 The symbol for micro is the Greek letter mu, often written u
60 in an ASCII context where this Greek letter is not available.
64 http://physics.nist.gov/cuu/Units/prefixes.html
67 The binary prefixes resemble the decimal ones,
68 but have an additional \(aqi\(aq
69 (and "Ki" starts with a capital \(aqK\(aq).
70 The names are formed by taking the
71 first syllable of the names of the decimal prefix with roughly the same
72 size, followed by "bi" for "binary".
78 Mi mebi 2^20 = 1048576
79 Gi gibi 2^30 = 1073741824
80 Ti tebi 2^40 = 1099511627776
81 Pi pebi 2^50 = 1125899906842624
82 Ei exbi 2^60 = 1152921504606846976
89 http://physics.nist.gov/cuu/Units/binary.html
92 Before these binary prefixes were introduced, it was fairly
93 common to use k=1000 and K=1024, just like b=bit, B=byte.
94 Unfortunately, the M is capital already, and cannot be
95 capitalized to indicate binary-ness.
97 At first that didn't matter too much, since memory modules
98 and disks came in sizes that were powers of two, so everyone
99 knew that in such contexts "kilobyte" and "megabyte" meant
100 1024 and 1048576 bytes, respectively.
101 What originally was a
102 sloppy use of the prefixes "kilo" and "mega" started to become
103 regarded as the "real true meaning" when computers were involved.
104 But then disk technology changed, and disk sizes became arbitrary numbers.
105 After a period of uncertainty all disk manufacturers settled on the
106 standard, namely k=1000, M=1000k, G=1000M.
108 The situation was messy: in the 14k4 modems, k=1000; in the 1.44MB
109 .\" also common: 14.4k modem
110 diskettes, M=1024000; etc.
111 In 1998 the IEC approved the standard
112 that defines the binary prefixes given above, enabling people
113 to be precise and unambiguous.
115 Thus, today, MB = 1000000B and MiB = 1048576B.
117 In the free software world programs are slowly
118 being changed to conform.
119 When the Linux kernel boots and says
123 hda: 120064896 sectors (61473 MB) w/2048KiB Cache
127 the MB are megabytes and the KiB are kibibytes.