For computer experts focused solely on performance, June and November
mark the twice-yearly release of the TOP500 list, which ranks the
world's supercomputers in terms of "teraflops," or trillions of
calculations per second (the "flop" comes from "floating-point
operations," a technical term for computer calculations). That list is
currently led by a supercomputer at DOE's Lawrence Livermore National
Laboratory (LLNL) that has a peak speed of more than 596 teraflops.
But the November 2007 list of supercomputing speed freaks was accompanied
by a newcomer, the Green500 list, which reworks the TOP500 list in
terms of energy efficiency. The Green500 list ranks the 500 fastest
supercomputers by megaflops per watt, that is, by how many thousands
of calculations are performed per watt of energy consumed.