# Seth Woolley's Man Viewer

## Manual for units - man 7 units

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```UNITS(7)                   Linux Programmer's Manual                  UNITS(7)

NAME
units(1,7), kilo, kibi, mega, mebi, giga, gibi - decimal and binary prefixes

DESCRIPTION
Decimal prefixes
The SI system of units(1,7) 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
u        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(1,8)  an

http://physics.nist.gov/cuu/Units/prefixes.html

Binary prefixes
The  binary  prefixes resemble the decimal ones, but have an additional
'i' (and "Ki" starts with a capital 'K'). The names are formed by  tak-
ing  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

http://physics.nist.gov/cuu/Units/binary.html

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(1,8) sizes that were powers of two, so everyone knew  that  in(1,8)  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=1000k, G=1000M.

The  situation  was  messy:  in(1,8)  the 14k4 modems, k=1000; in(1,8) the 1.44MB
diskettes, M=1024000; etc. In 1998 the IEC approved the  standard  that
defines  the binary prefixes given above, enabling people to be precise
and unambiguous.

Thus, today, MB = 1000000B and MiB = 1048576B.

In the free software world programs are slowly being  changed  to  con-
form. When the Linux kernel boots and says

hda: 120064896 sectors (61473 MB) w/2048KiB Cache

the MB are megabytes and the KiB are kibibytes.

Linux                             2001-12-22                          UNITS(7)
```