atto ==>
prefix
1. <unit> The standard metric prefixes used in the Système International
d'Units (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). This common practice goes against the edicts of the
BIPM who deprecate the use of these prefixes for powers of two. 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.
The unit is often dropped so one may talk of "a 40K salary" (40000 dollars) or
"2 meg of disk space" (2*2^20 bytes).
The accepted pronunciation of the initial G of "giga" is hard, /gi'ga/.
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. For example, 3.5" microfloppies are often described
as storing "1.44 MB". In fact, this is completely specious. The correct size is
1440 KB = 1440 * 1024 = 1474560 bytes. Alas, this point is probably lost on the
world forever.
In 1993, hacker Morgan Burke proposed, to general approval on Usenet, the
following additional prefixes: groucho (10^30), harpo (10^27), harpi (10^27),
grouchi (10^30). 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.
2. <language> Related to the prefix notation.
(20030506)
Nearby terms:
predomain « preemptive multitasking « prefetch «
prefix
» prefix notation » prefix syntax » preorder
