Provided by: manpages_6.8-2_all

#### 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
q        quecto   10^-30 = 0.000000000000000000000000000001
r        ronto    10^-27 = 0.000000000000000000000000001
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
µ        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
R        ronna    10^27  = 1000000000000000000000000000
Q        quetta   10^30  = 1000000000000000000000000000000

The symbol for micro is the Greek letter mu, often written u in  an  ASCII  context  where
this Greek letter is not available.

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 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
Zi       zebi   2^70 = 1180591620717411303424
Yi       yobi   2^80 = 1208925819614629174706176

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.

```

#### SEEALSO

```       The  International   System   of   Units   ⟨https://www.bipm.org/documents/20126/41483022/
SI-Brochure-9.pdf⟩.
```