Wikipedia: Prefix

Merge with SI prefix and move there, as that page has the better name

1. <unit> The standard metric prefixes used in the SI (Systeme 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 speech, 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. [Is this true of Commonwealth countries?]

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.

2. Related to the prefix notation.

This article (or an earlier version of it) contains material from FOLDOC, used with permission.

(redirected from Kilo-)

Prefix