KNOXVILLE, Tenn. -- The most powerful supercomputer available for general scientific research in the United States has undergone an upgrade that's doubled its peak performance.

The Cray XT3 supercomputer at Tennessee's Oak Ridge National Laboratory can now perform up to 54 trillion calculations per second -- up from its previous peak of 25 trillion calculations, or teraflops.

"It is probably the fifth-fastest machine" in the world, said Thomas Zacharia, associate laboratory director. "It is clearly the fastest open-science machine in the U.S. today."

The supercomputer, dubbed "Jaguar," was previously ranked the 13th most powerful in a list compiled by computer scientists at the University of Mannheim, Lawrence Berkeley National Laboratory and the University of Tennessee.

"The list is a very simple measure, and it is a good thing, obviously," Zacharia said.

The overhaul was the first step in a multiyear, nearly $200 million contract between Seattle-based Cray Inc. and the Department of Energy to increase Oak Ridge's supercomputing capability to 1,000 trillion calculations per second, or one petaflop, by 2009.