Yep, Beowulf clusters ... Seems to be extremely efficient if you
don't need a very fine grained parallelism.
http://cesdis.gsfc.nasa.gov/linux/beowulf/
This is similar to the Alpha farm on which the Titanic film effect were
rendered. The CalTech Beowulf machine is really impressive, 140 PPro 200
with 128 Mb of Ram each ....
http://www.cacr.caltech.edu/research/beowulf/
Daniel