IBM and its Blue Gene supercomputer again claimed the top spot in the Top500 supercomputer rankings. IBM also had the most systems on the list with 259, followed by Hewlett-Packard with 131.

The No. 1 position was claimed by the Blue Gene/L System, a joint development between IBM and the Department of Energy's National Nuclear Security Administration and installed at the department's Lawrence Livermore National Laboratory in Livermore, Calif. The system has a Linpack benchmark performance of 136.8 teraflops per second.

Second on the list is also a Blue Gene system installed at IBM's Thomas J. Watson Research Center in Yorktown, N.Y., benchmarked at 91.2 teraflops.

A total of 333 of the top 500 systems were based on Intel processors, up from 320 in the last listing six months ago. The second-most-common processor is the IBM Power with 77 systems, followed by Hewlett-Packard's PA RISC with 26, and Advanced Micro Devices processors at 25.

A total of 294 of the 500 systems are based in the United States. Europe was second with 114 systems, followed by Asian countries with 58 systems.

The Top500 list is compiled by Hans Meur of the University of Mannheim, Germany; Erich Strohmaier and Horst Simon of NER C/Lawrence Berkeley National Laboratory; and Jack Dongarra of the University of Tennessee, Knoxville.