A supercomputer built by the Chinese government has retained its crown as the world's most powerful system in the latest ranking by a German university. The Top500 list of the globe's fastest and most powerful supercomputers is compiled twice a year by researchers at the University of Mannheim. Topping the latest list is China's Tianhe-2, which can chew through computation at 33.86 petaflops per second, or 33,863 trillion calculations per second. In second place was the IBM-Built Titan, which scored 17.59 petaflop/sec. IBM scientists said they believe the way the list was calculated should be updated and would campaign for the change at a conference being held this week in Denver, Colorado. "The Top500 has been a very useful tool in the past decades to try to have a single number that could be used to measure the performance and the evolution of high-performance computing," Alessandro Curioni, head of the computational sciences department at IBM's Zurich research lab, told the BBC. "[But] today we need a more practical measurement that reflects the real use of these supercomputers based on their most important applications." Computer scientist Alan Woodward of Britain's University of Surrey agreed. "Talking about the number of calculations that can be carried out per second isn't the same as saying a supercomputer can do that in practice in a sustained way," he said. "The processors might be kicking their heels some of the time if they don't get the data as fast as they can handle, for example." The Tianhe-2 was built by China's National University of Defense Technology.