1UNITS(7) Linux Programmer's Manual UNITS(7)
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6 units, kilo, kibi, mega, mebi, giga, gibi - decimal and binary prefixes
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9 Decimal prefixes
10 The SI system of units uses prefixes that indicate powers of ten. A
11 kilometer is 1000 meter, and a megawatt is 1000000 watt. Below the
12 standard prefixes.
13 Prefix Name Value
15 y yocto 10^-24 = 0.000000000000000000000001
16 z zepto 10^-21 = 0.000000000000000000001
17 a atto 10^-18 = 0.000000000000000001
18 f femto 10^-15 = 0.000000000000001
19 p pico 10^-12 = 0.000000000001
20 n nano 10^-9 = 0.000000001
21 µ micro 10^-6 = 0.000001
22 m milli 10^-3 = 0.001
23 c centi 10^-2 = 0.01
24 d deci 10^-1 = 0.1
25 da deka 10^ 1 = 10
26 h hecto 10^ 2 = 100
27 k kilo 10^ 3 = 1000
28 M mega 10^ 6 = 1000000
29 G giga 10^ 9 = 1000000000
30 T tera 10^12 = 1000000000000
31 P peta 10^15 = 1000000000000000
32 E exa 10^18 = 1000000000000000000
33 Z zetta 10^21 = 1000000000000000000000
34 Y yotta 10^24 = 1000000000000000000000000
35 The symbol for micro is the Greek letter mu, often written u in an
37 ASCII context where this Greek letter is not available. See also
38 ⟨http://physics.nist.gov/cuu/Units/prefixes.html⟩
40 Binary prefixes
42 The binary prefixes resemble the decimal ones, but have an additional
43 'i' (and "Ki" starts with a capital 'K'). The names are formed by tak‐
44 ing the first syllable of the names of the decimal prefix with roughly
45 the same size, followed by "bi" for "binary".
46 Prefix Name Value
48 Ki kibi 2^10 = 1024
49 Mi mebi 2^20 = 1048576
50 Gi gibi 2^30 = 1073741824
51 Ti tebi 2^40 = 1099511627776
52 Pi pebi 2^50 = 1125899906842624
53 Ei exbi 2^60 = 1152921504606846976
54 See also
56 ⟨http://physics.nist.gov/cuu/Units/binary.html⟩
58 Discussion
60 Before these binary prefixes were introduced, it was fairly common to
61 use k=1000 and K=1024, just like b=bit, B=byte. Unfortunately, the M
62 is capital already, and cannot be capitalized to indicate binary-ness.
63 At first that didn't matter too much, since memory modules and disks
65 came in sizes that were powers of two, so everyone knew that in such
66 contexts "kilobyte" and "megabyte" meant 1024 and 1048576 bytes,
67 respectively. What originally was a sloppy use of the prefixes "kilo"
68 and "mega" started to become regarded as the "real true meaning" when
69 computers were involved. But then disk technology changed, and disk
70 sizes became arbitrary numbers. After a period of uncertainty all disk
71 manufacturers settled on the standard, namely k=1000, M=1000k, G=1000M.
72 The situation was messy: in the 14k4 modems, k=1000; in the 1.44MB
74 diskettes, M=1024000; etc. In 1998 the IEC approved the standard that
75 defines the binary prefixes given above, enabling people to be precise
76 and unambiguous.
77 Thus, today, MB = 1000000B and MiB = 1048576B.
79 In the free software world programs are slowly being changed to con‐
81 form. When the Linux kernel boots and says
82 hda: 120064896 sectors (61473 MB) w/2048KiB Cache
84 the MB are megabytes and the KiB are kibibytes.
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88 This page is part of release 3.53 of the Linux man-pages project. A
89 description of the project, and information about reporting bugs, can
90 be found at http://www.kernel.org/doc/man-pages/.
91Linux 2012-08-05 UNITS(7)