JargonFile/entries/quantifiers.txt

quantifiers

In techspeak and jargon, the standard metric prefixes used in the SI (Systeme
International) conventions for scientific measurement have dual uses. 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. But 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 decimal
interpretations in common use:

kilo  (K, KB)  1,024
mega  (M, MB)  1,048,576
giga  (G, GB)  1,073,741,824
tera  (T, TB)  1,099,511,627,776
peta  (P, PB)  1,125,899,906,842,624
exa   (EX)     1,152,921,504,606,846,976<37>
zetta          1,180,591,620,717,411,303,424
yotta          1,208,925,819,614,629,174,706,176

Here are the SI fractional prefixes:

milli  1000^-1
micro  1000^-2
nano   1000^-3
pico   1000^-4
femto  1000^-5
atto   1000^-6
zepto  1000^-7
yocto  1000^-8

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 1/1000, 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). See the entries on micro-, pico-, and nano- for more information
on connotative jargon use of these terms. ‘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).

There are, of course, some standard unit prefixes for powers of 10. In
the following table, the ‘prefix’ column is the international standard
prefix for the appropriate power of ten; the ‘binary’ column lists
jargon abbreviations and words for the corresponding power of 2. The
B-suffixed forms are commonly used for byte quantities; the words ‘meg’
and ‘gig’ are nouns that may (but do not always) pluralize with ‘s’.

Confusingly, hackers often use K or M as though they were suffix or
numeric multipliers rather than a prefix; thus “2K dollars”, “2M of
disk space”. This is also true (though less commonly) of G.

Note that the formal SI metric prefix for 1000 is ‘k’; some use this
strictly, reserving ‘K’ for multiplication by 1024 (KB is thus
‘kilobytes’).

K, M, and G used alone refer to quantities of bytes; thus, 64G is
64 gigabytes and ‘a K’ is a kilobyte (compare mainstream use of
‘a G’ as short for ‘a grand’, that is, $1000). Whether one
pronounces ‘gig’ with hard or soft ‘g’ depends on what one thinks
the proper pronunciation of ‘giga-’ is.

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" floppies
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.