IBM's Blue Gene/L supercomputer has kept its position as the most powerful number cruncher in the world.

An IBM-built computer that has topped the list of the world's 500 most powerful supercomputers has widened its lead in the latest ranking released Monday.

The computer named Blue Gene/L, deployed at Lawrence Livermore National Laboratory, has doubled its performance to 280.6 trillion calculations per second (teraflops), up from 136.8 teraflops from the list released in June.

The system, which is used to study the U.S. nuclear stockpile and perform other research, was officially completed this summer after it was doubled in size. Researchers expect it will hold the top spot for the foreseeable future.

IBM built the top three systems on the list released today by the Top 500 project, an independent group of university computer scientists who release supercomputer rankings every six months.

Big Blue built 43.8 percent of the systems on the entire list.

The No. 2 machine is another Blue Gene system, with performance ranked at 91.2 teraflops. It's installed at IBM's Thomas Watson Research Center. The No. 3 system, also at LLNL, reached 63.4 teraflops in the test.

Hewlett-Packard is the No. 2 manufacturer, with 33.8 percent of the machines on the list. No other computer maker has more than 7 percent in any category.

Of the chip makers, Intel microprocessors were used in a total of 333 systems, with 81 using the company's EM64T technology. IBM chips are in second place, with its Power microprocessors at the heart of 73 systems.

AMD's Opteron chips were used in 55 systems, up from 25 six months ago.

Of all the systems, the majority -- 305 -- are installed in the United States. Europe is represented by 100 systems on the list, while Asia has 66.

Japan's Earth Simulator, which topped five lists until it was dethroned by Blue Gene/L's prototype last November, slipped to the No. 7 spot. It was a source of much American angst when it first topped the list in 2002.

The latest list will be released officially Tuesday at a supercomputer conference in Seattle.