IBM captured the number one and six of the top 10 positions in a ranking released Thursday of the world's most powerful supercomputers.

ASCI White, IBM's classified supercomputer used for nuclear weapons research at the Lawrence Livermore National Laboratory in California, was ruled the world's most powerful, followed by the company's machine at the NERSC (National Energy Research Scientific Computing Center[sic]), also in California.

IBM officially announced delivery Thursday of the NERSC machine, capable of a theoretical peak of 3.8 trillion calculations per second (3.8 teraflops), said Dave Gelardi, director of high-performance computing at IBM.

The Top 500 list, published every six months by researchers from University of Tennessee and the University of Mannheim, was made public at the Supercomputing 2001 Conference this week in Heidelberg, Germany. Researchers measure supercomputers' speed and power using a benchmarking standard called the Linpack test.

IBM also dominated the previous list, released in November 2000, with ASCI White taking first place and Big Blue machines in five of the top 10 positions.

Third place went to Intel's ASCI Red, at Sandia National Laboratories in New Mexico. IBM took fourth for its ASCI Blue-Pacific machine, also at Lawrence Livermore, and fifth-place honours went to Hitachi for its SR8000/MPP, at the University of Tokyo.

IBM and NERSC worked for two years on the computing system that joins 158 servers and over 2,400 processors.

Scientists from around the world can use the NERSC systems by submitting research proposals to a peer group that judges the merits of the research and how ready the scientists are to use the computer. Researchers will use the NERSC systems to study areas such as the human genome, global climate patterns and the energy efficiency of buildings and cities, said Bill Kramer, head of high performance computing at NERSC in Berkeley, California.

Around 65 technicians manage the NERSC systems and prepare them for research use.