The U.S., once again, is home to the world's most powerful supercomputer after being knocked off the list by China two years ago and Japan last year.

The top computer, an IBM system at the Department of Energy's Lawrence Livermore National Laboratory, is capable of 16.32 sustained petaflops, according to the Top 500 list, a global, twice a year ranking, released Monday.

This system, named Sequoia, has more than 1.57 million compute cores and relies on architecture and parallelism, and not Moore's Law, to achieve its speeds.

"We're at the point where the processors themselves aren't really getting any faster," said Michael Papka, Argonne National Laboratory deputy associate director for computing, environment and life sciences.

The Argonne lab installed a similar IBM system, which ranks third on the new Top 500 list. "Moore's Law is generally slowing down and we're doing it (getting faster speeds) by parallelism," Papka said.

U.S. high performance computing technology dominates the world market. IBM systems claimed five of the top ten spots in the list, and 213 systems out the 500.

Hewlett-Packard is number two, with 141 systems on the list. Nearly 75% of the systems on this list run Intel processors, and 13% use AMD chips.

Despite the continuing strength of U.S. vendors globally, when China's supercomputer took the top position in June, 2010, it seemed to hit a national nerve.

President Barack Obama mentioned China's top ranked supercomputer in two separate speeches, including his State of the Union address last year.

Steven Chu, the U.S. DOE secretary and a Nobel Prize winner in physics, warned that America's innovation leadership was at risk.

The latest Top 500 list will not change concerns about competitive threats to U.S. technological leadership.

Just this weekend, China launched its fourth manned space mission, sending its first woman into space. The U.S. ended its space shuttle program last year. China is also is developing its own processors to reduce its dependency on Western components.

But the U.S., for now, is leading the world in supercomputers.

The top system marks the first time that IBM has introduced water cooling in its supercomputers. The third place system, Mira, which is also a BlueGene system, also uses water cooling to help remove heat generated by more than 786,000 compute cores.

The Sequoia is more than double the number of compute cores of the second system on the list, Japan's K computer, which had been ranked first at 10.51 petaflops.

Along with the most first and third most powerful computer, IBM also has fourth place with a German system built for the Leibniz-Rechenzentrum computer center for Munich's universities. Two other BlueGene/Q systems, one for Italy and another for Germany, occupy seventh and eighth spots on the list.

The most striking thing about the list, said Jack Dongarra, a professor of computer science at the University of Tennessee and one of the people behind the Top 500 program, is that more than half of the machines on this list aren't deployed in research, academic settings or by government. "More than half are used by industry," he said.

"Industry gets it," said Dongarra. "These machines are important; they can provide some competitive advantage," he said.

The Europeans, in particular, are moving aggressively to build out supercomputing capability, despite all the troubles their economies are facing.

"The Europeans weren't keeping pace," said Dongarra, "and today we see resurgence (in Europe) in high performance computing."