[1] : Jargon File (4.3.1, 29 Jun 2001)

quantifiers in techspeak and jargon, the standard metric prefixes used
   in the si syste`me 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
   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 usage_
  milli-  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       pronunciation
  kilo-       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.

   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.

   1993 update: hacker morgan burke has proposed, to general approval on
   usenet, the following additional prefixes:

   groucho
  10^-30
  
   harpo
  10^-27
  
   harpi
  10^27
  
   grouchi
  10^30
  
   we observe that 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.

   1999 upate: there is an iec proposal
   ftp://ftp.informatik.uni-erlangen.de/pub/doc/iso/information-units for
   binary multipliers, but no evidence that any of its proposals are in
   live use.


see also:
micro- nano- pico- attoparsec marketroid microfloppies 
bogus 

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