My branch uses a Beowulf cluster for simulating atmospheric entry of interplanetary spacecraft. I cajoled my branch into buying the thing one step at a time (everyone was initially locked into the Cray main frame mind set). The cluster that we got was based upon DEC (now Compaq/Samsung) Alphas. I first demonstrated that Alphas were fast by convincing them to buy me one as a work station. My machine ran on Linux and was very fast for a single CPU box. After I convinced them that Alphas were a good thing, we bought a small cluster of thirteen nodes each based upon 650 MHz Alphas. Everything runs on Linux (Windows NT is not stable enough to run on a Beowulf cluster). Our Beowulf ran quite nicely so we then added four more nodes each with dual processors running at 850 MHz. Two of these nodes have the same floating point power as one CPU on an old Cray C90. The whole array costs less than $150,000. Beowulf clusters have outstanding performance/cost and are the only way to go for scientific computing. However they are definitely "roll your own computing". You have to assemble the hardware yourself and fiddle with the operating system (lots of tricky sysadmin). Not for the faint hearted.

Gary