UNITS
Section: Linux Programmer's Manual (7)
Updated: 2017-09-15
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NAME
units - decimal and binary prefixes
DESCRIPTION
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.
-
| Prefix | Name | Value
|
| y | yocto | 10^-24 = 0.000000000000000000000001
|
| z | zepto | 10^-21 = 0.000000000000000000001
|
| a | atto | 10^-18 = 0.000000000000000001
|
| f | femto | 10^-15 = 0.000000000000001
|
| p | pico | 10^-12 = 0.000000000001
|
| n | nano | 10^-9 = 0.000000001
|
| mc | micro | 10^-6 = 0.000001
|
| m | milli | 10^-3 = 0.001
|
| c | centi | 10^-2 = 0.01
|
| d | deci | 10^-1 = 0.1
|
| da | deka | 10^ 1 = 10
|
| h | hecto | 10^ 2 = 100
|
| k | kilo | 10^ 3 = 1000
|
| M | mega | 10^ 6 = 1000000
|
| G | giga | 10^ 9 = 1000000000
|
| T | tera | 10^12 = 1000000000000
|
| P | peta | 10^15 = 1000000000000000
|
| E | exa | 10^18 = 1000000000000000000
|
| Z | zetta | 10^21 = 1000000000000000000000
|
| Y | yotta | 10^24 = 1000000000000000000000000
|
The symbol for micro is the Greek letter mu, often written u
in an ASCII context where this Greek letter is not available.
See also
-
Binary prefixes
The binary prefixes resemble the decimal ones,
but have an additional aqiaq
(and "Ki" starts with a capital aqKaq).
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".
-
| Prefix | Name | Value
|
| Ki | kibi | 2^10 = 1024
|
| Mi | mebi | 2^20 = 1048576
|
| Gi | gibi | 2^30 = 1073741824
|
| Ti | tebi | 2^40 = 1099511627776
|
| Pi | pebi | 2^50 = 1125899906842624
|
| Ei | exbi | 2^60 = 1152921504606846976
|
See also
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.
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.
The situation was messy: in the 14k4 modems, k=1000; in the 1.44 MB
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.
Thus, today, MB = 1000000 B and MiB = 1048576 B.
In the free software world programs are slowly
being changed to conform.
When the Linux kernel boots and says
hda: 120064896 sectors (61473 MB) w/2048KiB Cache
the MB are megabytes and the KiB are kibibytes.
COLOPHON
This page is part of release 4.13 of the Linux
man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
https://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- DESCRIPTION
-
- Decimal prefixes
-
- Binary prefixes
-
- Discussion
-
- COLOPHON
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- Running on 
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