Re: Dumb Question Mk II

["J. J. Rozental" <josrozen@netmedia.net.il>]

At 12:33 PM 7/17/98 -0500, you wrote:
>SI UNIT PREFIXES:
>
>T tera    10E12 (million million)
>P peta    10E15
>E exa     10E18
>
>Thats as high as I go!
>
>Mario Iannaccone
>NH DHSS/BRH
>Health Physicist
>miannacc@dhhs.state.nh.us
>
>

Mario, Bob Giansiracusa, and others' interested

GO TO http://www.cacr.caltech.edu/~roy/dataquan/ety.html

Etymology of Units



   1.Kilo Greek khilioi = 1000 
   2.Mega Greek megas = great, e.g., Alexandros Megos 
   3.Giga Latin gigas = giant 
   4.Tera Greek teras = monster 
   5.Peta Greek pente = five, fifth prefix, peNta - N = peta 
   6.Exa Greek hex = six, sixth prefix, Hexa - H = exa
     Remember, in standard French, the initial H is silent, so they would
pronounce Hexa as  Exa. It is far easier to call it Exa for everyone's sake,
right? 
   7.Zetta almost homonymic with Greek Zeta, but last letter of the Latin
alphabet 
   8.Yotta almost homonymic with Greek iota, but penultimate letter of the
Latin alphabet. 

The first prefix is number-derived; second, third, and fourth are based on
mythology. Fifth and  sixth are supposed to be just that: fifth and sixth.
But, with the seventh, another fork has been taken. The General Conference
of Weights and Measures (CGMP, from the French; they have been
headquartered, since 1874, in Sevres on the outskirts of Paris) has now
decided to name the prefixes, starting with the seventh, with the letters of
the Latin alphabet, but starting from the
end. Now, that makes it all clear! Remember, both according to CGMP and SI,
the prefixes refer to powers of 10. Mega is 10**6, exactly 1,000,000, kilo
is exactly 1000, not 1024. 

========================================== 
GO TO http://www.sdsc.edu/GatherScatter/gsq394/gsq3_f1.html
The peta- principle

by Jim Binder

Jim Binder is a technical editor at SDSC. This article was written with
document retrieval
assistance from Dick Ellis, SDSC librarian. 
                    

Since shortly after the French Revolution of 1789, scientists--and
eventually computer scientists--have found it convenient to refer to large
quantities of various units of measure with  verbal prefixes and letter
symbols. Thus kilo- (symbol K) and mega- (M) stand for 10**3 and 10**6,
thousands and millions. After World War II, this pair of terms was extended,
three zeroes at a time, to giga- (G) and tera- (T), standing for 10**9 and
10**12, billions and trillions (usage here and below is American). In 1975,
the world arbiter of the metric system, the
General Conference of Weights and Measures (CGPM), based at Sevres near
Paris, agreed to add two more terms to the ascending series: peta- (P) and
exa- (E) for 10**15 and 10**18, quadrillions and quintillions. 

The creation of these newest terms is interesting. The older prefixes,
kilo-, mega-, giga-, and tera-, are generally understood to be derived from
the ancient Greek words for "thousand," "large," "giant," and "monster,"
respectively. But peta- departs from the traditional pattern to the extent
that there is no Greek (or any other) word to explain it in its present form. 

Considering the context, however, (preceding exa-) it is the Greek prefix
for "five," penta-, minus the letter "n." The reduction of five letters to
four makes it similar in this respect to the existing prefixes. On the other
hand, exa- has been reduced to three letters by dropping the "h" from hexa-,
the Greek prefix for "six," possibly because the "h" would be silent in
standard French. 

According to a CGPM report, prefixes meaning "five" and "six" are used
because 10**15 and  10**18 are fifth and sixth in the ascending series
10**3, 10**6, 10**9, and 10**12. 

(If tera- for 10**12 were taken to mean the Greek prefix for "four,"
te(t)ra-, minus the second letter "t," that would be an additional reason
for its being followed by pe(n)ta- as the prefix for "five." However, the
acceptance of tera- as derived from "teras," the Greek word for "monster,"
seems to be universal.) 

The use of Greek words for magnitudes through 10**12 turns out to be awkward
in the late  twentieth century, since it is difficult to extend the series
easily. (After all, what could be bigger than giants and monsters?) Yet it
would be even more awkward to throw away the established size-words and
start from scratch. Therefore, a backward switch in midstream from a
Greek-conceptual to the original Greek-numerical basis (using kilo- for
"thousand") is announced as the "expedient" thing to do, simultaneously
preserving tradition and leaving the way open to further expansion. 

Since 1975, though, and so quietly that current editions of the Encyclopedia
Brittanica and  World Almanac do not recognize their advent, prefixes with
corresponding symbols have  materialized for 10**21 and 10**24: zetta- (Z)
and yotta- (Y), denoting sextillions and septillions. With these it is easy
to see yet another change of direction. While still disyllabic, the names
are now semi-artificial (echoing Greek zeta and iota) and symbol-driven, and
the series is
now based on the Latin alphabet, starting with the last letter and moving 
backwards, with a long way to go before reaching A.

 Could this be the last terminological contortion? 

Jose Julio Rozental <josrozen@netmedia.net.il>
Israel