Originální popis anglicky:
units, kilo, kibi, mega, mebi, giga, gibi - decimal and binary 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 |
| 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 an ASCII context
where this Greek letter is not available. See also
http://physics.nist.gov/cuu/Units/prefixes.html
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 |
See also
http://physics.nist.gov/cuu/Units/binary.html
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=1000k, G=1000M.
The situation was messy: in the 14k4 modems, k=1000; in 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 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.
