prefix
1. The standard metric prefixes used in the SI
(Syst`eme International) conventions for scientific
measurement. With units of time or things that come in powers
of 10, such as money, they retain their usual meanings of
multiplication by powers of 1000 ◦ 10^3. When used with bytes
or other things that naturally come in powers of 2, they
usually denote multiplication by powers of 1024 ◦ 2^(10).
Here are the SI magnifying prefixes, along with the
corresponding binary interpretations in common use:
prefix abr decimal binary
yocto- 1000^-8
zepto- 1000^-7
atto- 1000^-6
femto- f 1000^-5
pico- p 1000^-4
nano- n 1000^-3
micro- ▫ 1000^-2 ▫ Abbreviation: Greek mu
milli- m 1000^-1
kilo- k 1000^1 1024^1 ◦ 2^10 ◦ 1,024
mega- M 1000^2 1024^2 ◦ 2^20 ◦ 1,048,576
giga- G 1000^3 1024^3 ◦ 2^30 ◦ 1,073,741,824
tera- T 1000^4 1024^4 ◦ 2^40 ◦ 1,099,511,627,776
peta- 1000^5 1024^5 ◦ 2^50 ◦ 1,125,899,906,842,624
exa- 1000^6 1024^6 ◦ 2^60 ◦ 1,152,921,504,606,846,976
zetta- 1000^7 1024^7 ◦ 2^70 ◦ 1,180,591,620,717,411,303,424
yotta- 1000^8 1024^8 ◦ 2^80 ◦ 1,208,925,819,614,629,174,706,176
The prefixes zetta-, yotta-, zepto-, and yocto- have been
included in these tables purely for completeness and giggle
value; they were adopted in 1990 by the "19th Conference
Generale des Poids et Mesures". The binary peta- and exa-
loadings, though well established, are not in jargon use
either - yet. The prefix milli-, denoting multiplication by
1000^(-1), has always been rare in jargon (there is, however,
a standard joke about the "millihelen" - notionally, the
amount of beauty required to launch one ship). "Femto" and
"atto" (which, interestingly, derive not from Greek but from
Danish) have not yet acquired jargon loadings, though it is
easy to predict what those will be once computing technology
enters the required realms of magnitude (however, see
{attoparsec}).
The abbreviated forms of these prefixes are common in
electronics and physics. k, M and G are also common in
computing where they stand for powers of two more often than
powers of ten. Thus "MB" stands for megabytes (2^20 bytes).
In speach, the unit is often dropped so one may talk of "a 40K
salary" (40000 dollars) or "2M of disk space" (2▫2^20 bytes).
The accepted pronunciation of the initial G of "giga-" was
once soft, /ji'ga/ (like "gigantic"), but now the hard
pronunciation, /gi'ga/, is probably more common.
Note that the formal SI metric prefix for 1000 is lower case
"k"; some, including this dictionary, use this strictly,
reserving "K" for multiplication by 1024 (KB is thus
"kilobytes").
Confusing 1000 and 1024 (or other powers of 2 and 10 close in
magnitude) - for example, describing a memory in units of 500K
or 524K instead of 512K - is a sure sign of the {marketroid}.
One example of this: it is common to refer to the capacity of
3.5" {microfloppies} as "1.44 MB" In fact, this is a
completely {bogus} number. The correct size is 1440 KB, that
is, 1440 ▫ 1024 ◦ 1474560 bytes. So the "mega" in "1.44 MB"
is compounded of two "kilos", one of which is 1024 and the
other of which is 1000. The correct number of megabytes would
of course be 1440 / 1024 ◦ 1.40625. Alas, this fine point is
probably lost on the world forever.
In 1993, hacker Morgan Burke proposed, to general approval on
{Usenet}, the following additional prefixes: groucho (10^-30),
harpo (10^-27), harpi (10^27), grouchi (10^30). This would
leave the prefixes zeppo-, gummo-, and chico- available for
future expansion. Sadly, there is little immediate prospect
that Mr. Burke's eminently sensible proposal will be ratified.
2. Related to the {prefix notation}.
(1998-05-09)