ASCI White is now #3 on the
Top 500 supercomputer list. It resides at the
Lawrence Livermore National Laboratory where it simulates
nuclear reactions. It can perform 12.3
TFLOPS peak/7.3 TFLOPS max; the
NEC Earth Simulator handily trounces it, but keep in mind this was state-of-the-art at one time.
ASCI White is composed of 8192 Power3 processors (512 16-processor RS/6000s), weighs 106 tons, and cost $110 million to build. It runs a parallelized version of AIX. This is not your father's supercomputer.
Information gleaned from http://www.top500.org/ and http://www.llnl.gov/asci/platforms/white/