2 .\" Copyright (C) 2001 Andries Brouwer <aeb@cwi.nl>
4 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
6 .TH units 7 (date) "Linux man-pages (unreleased)"
8 units \- decimal and binary prefixes
11 The SI system of units uses prefixes that indicate powers of ten.
12 A kilometer is 1000 meter, and a megawatt is 1000000 watt.
13 Below the standard prefixes.
18 q quecto 10\[ha]\-30 = 0.000000000000000000000000000001
19 r ronto 10\[ha]\-27 = 0.000000000000000000000000001
20 y yocto 10\[ha]\-24 = 0.000000000000000000000001
21 z zepto 10\[ha]\-21 = 0.000000000000000000001
22 a atto 10\[ha]\-18 = 0.000000000000000001
23 f femto 10\[ha]\-15 = 0.000000000000001
24 p pico 10\[ha]\-12 = 0.000000000001
25 n nano 10\[ha]\-9 = 0.000000001
26 \[mc] micro 10\[ha]\-6 = 0.000001
27 m milli 10\[ha]\-3 = 0.001
28 c centi 10\[ha]\-2 = 0.01
29 d deci 10\[ha]\-1 = 0.1
30 da deka 10\[ha] 1 = 10
31 h hecto 10\[ha] 2 = 100
32 k kilo 10\[ha] 3 = 1000
33 M mega 10\[ha] 6 = 1000000
34 G giga 10\[ha] 9 = 1000000000
35 T tera 10\[ha]12 = 1000000000000
36 P peta 10\[ha]15 = 1000000000000000
37 E exa 10\[ha]18 = 1000000000000000000
38 Z zetta 10\[ha]21 = 1000000000000000000000
39 Y yotta 10\[ha]24 = 1000000000000000000000000
40 R ronna 10\[ha]27 = 1000000000000000000000000000
41 Q quetta 10\[ha]30 = 1000000000000000000000000000000
45 The symbol for micro is the Greek letter mu, often written u
46 in an ASCII context where this Greek letter is not available.
48 The binary prefixes resemble the decimal ones,
49 but have an additional \[aq]i\[aq]
50 (and "Ki" starts with a capital \[aq]K\[aq]).
51 The names are formed by taking the
52 first syllable of the names of the decimal prefix with roughly the same
53 size, followed by "bi" for "binary".
58 Ki kibi 2\[ha]10 = 1024
59 Mi mebi 2\[ha]20 = 1048576
60 Gi gibi 2\[ha]30 = 1073741824
61 Ti tebi 2\[ha]40 = 1099511627776
62 Pi pebi 2\[ha]50 = 1125899906842624
63 Ei exbi 2\[ha]60 = 1152921504606846976
64 Zi zebi 2\[ha]70 = 1180591620717411303424
65 Yi yobi 2\[ha]80 = 1208925819614629174706176
69 Before these binary prefixes were introduced, it was fairly
70 common to use k=1000 and K=1024, just like b=bit, B=byte.
71 Unfortunately, the M is capital already, and cannot be
72 capitalized to indicate binary-ness.
74 At first that didn't matter too much, since memory modules
75 and disks came in sizes that were powers of two, so everyone
76 knew that in such contexts "kilobyte" and "megabyte" meant
77 1024 and 1048576 bytes, respectively.
79 sloppy use of the prefixes "kilo" and "mega" started to become
80 regarded as the "real true meaning" when computers were involved.
81 But then disk technology changed, and disk sizes became arbitrary numbers.
82 After a period of uncertainty all disk manufacturers settled on the
83 standard, namely k=1000, M=1000\ k, G=1000\ M.
85 The situation was messy: in the 14k4 modems, k=1000; in the 1.44\ MB
86 .\" also common: 14.4k modem
87 diskettes, M=1024000; and so on.
88 In 1998 the IEC approved the standard
89 that defines the binary prefixes given above, enabling people
90 to be precise and unambiguous.
92 Thus, today, MB = 1000000\ B and MiB = 1048576\ B.
94 In the free software world programs are slowly
95 being changed to conform.
96 When the Linux kernel boots and says
100 hda: 120064896 sectors (61473 MB) w/2048KiB Cache
104 the MB are megabytes and the KiB are kibibytes.
106 .UR https://www.bipm.org/\:documents/\:20126/\:41483022/\:SI\-Brochure\-9.pdf
107 The International System of Units