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diff --git a/man7/units.7 b/man7/units.7 new file mode 100644 index 0000000..ca2bd2d --- /dev/null +++ b/man7/units.7 @@ -0,0 +1,108 @@ +'\" t +.\" Copyright (C) 2001 Andries Brouwer <aeb@cwi.nl> +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.TH units 7 2023-02-10 "Linux man-pages 6.05.01" +.SH NAME +units \- decimal and binary prefixes +.SH DESCRIPTION +.SS 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. +.RS +.TS +l l l. +Prefix Name Value +q quecto 10\[ha]\-30 = 0.000000000000000000000000000001 +r ronto 10\[ha]\-27 = 0.000000000000000000000000001 +y yocto 10\[ha]\-24 = 0.000000000000000000000001 +z zepto 10\[ha]\-21 = 0.000000000000000000001 +a atto 10\[ha]\-18 = 0.000000000000000001 +f femto 10\[ha]\-15 = 0.000000000000001 +p pico 10\[ha]\-12 = 0.000000000001 +n nano 10\[ha]\-9 = 0.000000001 +\[mc] micro 10\[ha]\-6 = 0.000001 +m milli 10\[ha]\-3 = 0.001 +c centi 10\[ha]\-2 = 0.01 +d deci 10\[ha]\-1 = 0.1 +da deka 10\[ha] 1 = 10 +h hecto 10\[ha] 2 = 100 +k kilo 10\[ha] 3 = 1000 +M mega 10\[ha] 6 = 1000000 +G giga 10\[ha] 9 = 1000000000 +T tera 10\[ha]12 = 1000000000000 +P peta 10\[ha]15 = 1000000000000000 +E exa 10\[ha]18 = 1000000000000000000 +Z zetta 10\[ha]21 = 1000000000000000000000 +Y yotta 10\[ha]24 = 1000000000000000000000000 +R ronna 10\[ha]27 = 1000000000000000000000000000 +Q quetta 10\[ha]30 = 1000000000000000000000000000000 +.TE +.RE +.PP +The symbol for micro is the Greek letter mu, often written u +in an ASCII context where this Greek letter is not available. +.SS Binary prefixes +The binary prefixes resemble the decimal ones, +but have an additional \[aq]i\[aq] +(and "Ki" starts with a capital \[aq]K\[aq]). +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". +.RS +.TS +l l l. +Prefix Name Value +Ki kibi 2\[ha]10 = 1024 +Mi mebi 2\[ha]20 = 1048576 +Gi gibi 2\[ha]30 = 1073741824 +Ti tebi 2\[ha]40 = 1099511627776 +Pi pebi 2\[ha]50 = 1125899906842624 +Ei exbi 2\[ha]60 = 1152921504606846976 +Zi zebi 2\[ha]70 = 1180591620717411303424 +Yi yobi 2\[ha]80 = 1208925819614629174706176 +.TE +.RE +.SS 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. +.PP +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=1000\ k, G=1000\ M. +.PP +The situation was messy: in the 14k4 modems, k=1000; in the 1.44\ MB +.\" also common: 14.4k modem +diskettes, M=1024000; and so on. +In 1998 the IEC approved the standard +that defines the binary prefixes given above, enabling people +to be precise and unambiguous. +.PP +Thus, today, MB = 1000000\ B and MiB = 1048576\ B. +.PP +In the free software world programs are slowly +being changed to conform. +When the Linux kernel boots and says +.PP +.in +4n +.EX +hda: 120064896 sectors (61473 MB) w/2048KiB Cache +.EE +.in +.PP +the MB are megabytes and the KiB are kibibytes. +.SH SEE ALSO +.UR https://www.bipm.org/\:documents/\:20126/\:41483022/\:SI\-Brochure\-9.pdf +The International System of Units +.UE . |