China has regained the top spot on a list of the world’s most powerful supercomputers. The latest version of a semiannual ranking posted yesterday shows that Tianhe-2, built by China’s National University of Defense Technology, was clocked at 33.86 petaflops (a petaflop is a thousand trillion floating point operations per second). That’s nearly twice as powerful as the 17.59 Pflops performance of Titan, a supercomputer at Oak Ridge National Laboratory in Tennessee, which led the previous Top 500 list put out by a team of supercomputer researchers in the United States and Germany. Tianhe-2 marks the second time a Chinese machine has been a world-beater. Tianhe-1 grabbed the top spot in November 2010 before relinquishing it 6 months later to Japan’s K computer. China’s second ascent demonstrates the country’s sustained commitment to funding high performance computing, says Jack Dongarra, a computer scientist at the University of Tennessee, Knoxville, who closely follows international supercomputing trends. “It shows no signs of changing, only increasing,” Dongarra says about China’s investment in supercomputing. The United States remains the overall supercomputing leader, with 252 of the top 500 systems. But China is in second place, with 66 machines. Japan, the United Kingdom, France, and Germany fill out the top six, with 30, 29, 23, and 19 systems, respectively. 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The Tianhe-2 machine was built using more than 3 million Intel computing “cores,” essentially the brains of the machine. But Dongarra, who toured the site of the machine last month, says that most of the rest of the components were designed and built in China. “The interconnect, operating system, front-end processors, and software are mainly Chinese,” Dongarra says. The country is also hard at work developing its own high-end processor chips. If and when those are used as the brains of a top-of-the-line machine, “that will be a game-changer,” Dongarra says. It would signal that China no longer needs to rely on outside technology suppliers and also that the country is ready to compete with chipmakers Intel and AMD for the commercial chip market. Still, another supercomputer technology watcher who asked not to be identified due to his close ties with many of the companies involved says he believes that China has a ways to go to close the gap in processor chip technology. China’s surge in supercomputing also comes as the path forward for the U.S. supercomputing program has become obscured. The U.S. Department of Energy (DOE) has been considering a plan to build an exascale supercomputer, a next-generation machine 30 times more powerful than Tianhe-2. But that plan appears to be stuck in bureaucratic limbo. According to multiple sources on Capitol Hill that asked not to be identified, the plan has been bouncing back and forth between DOE and the Office of Management and Budget because of the Obama administration’s concerns about its projected $3 billion price tag. An exascale program appears to have strong backing among both Democrats and Republicans in the U.S. House of Representatives and the Senate. And House and Senate members have repeatedly asked DOE officials to give them an outline of the program so legislators can begin lining up funding. But DOE has already missed two deadlines. “We’re baffled,” says one Senate staffer about the administration’s apparent lack of interest. Another Hill staffer speculates that the exascale program may be a casualty of the numerous vacancies among top science officials at the DOE, who are in the best position to be its advocate. The program will also require a decade of sustained research funding to tackle the many technological challenges to building an exascale machine. “I don’t see how it is doable with the present technology,” says Horst Simon, a supercomputer expert at the Lawrence Berkeley National Laboratory in California. DOE is gearing up to build Trinity, a 30 Pflops supercomputer expected to go into operation by the end of 2015. By that date, however, China’s 5-year plan says that it will have built up to two 100 Pflops-scale machines. China hasn’t specified whether it will pursue an exascale machine as part of its next 5-year plan that begins in 2016. But as the Magic 8 ball says: “Signs Point to Yes.” *Correction, 11:40 a.m., 19 June: The correct abbreviation for petaflops is Pflops, not pflops. This has been fixed. Jack Dongarra Back on top. China’s Tianhe-2 supercomputer at the National University of Defense Technology.