The biannual Top500 supercomputers list is out. IBM retains the top spot with its BlueGene system at Lawrence Livermore National Laboratory. BlueGene's performance comes in at 280.6 trillion calculations per second. Of the ten most powerful supercomputers in the world, seven are in the U.S. with the other three in Japan, France and Spain. Overall, 306 of the top 500 systems are in the U.S.