# units of measure::prefixes::kilo, mega, giga, etc.

(source: Free On-line Dictionary of Computing (US, CA., mirror of Imperial College, London; now at http://foldoc.org/; this article is no longer available at that site) The standard metric prefixes used in the International System of Units (Système International, SI) (SI) conventions for scientific measurement.

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

```
"Femto" and "atto" derive not from Greek but from Danish.

The abbreviated forms of these prefixes are common in electronics and physics.

When used with bytes of storage, these prefixes usually denote multiplication by powers of 1024 = 2^10 (K, M, and G are common in computing). Thus "MB" stands for megabytes (2^20 bytes). The formal SI prefix for 1000 is lower case "k"; some, including this dictionary, use this strictly, reserving upper case "K" for multiplication by 1024 (KB is thus "kilobytes").

Also, in data transfer rates the prefixes stand for powers of ten so, for example, 28.8 kb/s means 28,800 bits per second.

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. Last modified Sun Jul 29 18:22:20 PDT 2007