Here are the SI magnifying prefixes, along with the corresponding binary interpretations in common use:
prefix decimal binary
kilo- 1000^1 1024^1 = 2^10 = 1,024
mega- 1000^2 1024^2 = 2^20 = 1,048,576
giga- 1000^3 1024^3 = 2^30 = 1,073,741,824
tera- 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
Here are the SI fractional prefixes:
prefix decimal jargon usagemilli- 1000^-1 (seldom used in jargon)
micro- 1000^-2 small or human-scale (see [micro-])
nano- 1000^-3 even smaller (see [nano-])
pico- 1000^-4 even smaller yet (see [pico-])
femto- 1000^-5 (not used in jargon---yet)
atto- 1000^-6 (not used in jargon---yet)
zepto- 1000^-7 (not used in jargon---yet)
yocto- 1000^-8 (not used in jargon---yet)
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 suffix 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'.
prefix decimal binary pronunciationkilo- k K, KB, /kay/
mega- M M, MB, meg /meg/
giga- G G, GB, gig /gig/,/jig/
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.