A Cray supercomputer at Oak Ridge National Laboratory has regained the title of the world's most powerful supercomputer, overtaking the installation that was ranked at the top in June, while China entered the Top 10 with a hybrid Intel-AMD system.

The upgraded Jaguar supercomputer at Oak Ridge now boasts a speed of 1.759 petaflops per second from its 224,162 cores, while the IBM Roadrunner system at the US Department of Energy's Los Alamos National Laboratory slowed slightly to 1.042 petaflops per second after it was repartitioned. A petaflop is one thousand trillion calculations per second.

The list of the Top 500 supercomputers, set to be released on Monday during the SC09 supercomputing conference, is compiled twice a year and is now in its 34th installment. The total capacity of the systems on the new list is 27.6 petaflops, up from 22.6 petaflops on the previous list in June.

Roadrunner debuted in June 2008 as the first computer to surpass 1 petaflop per second on the Linpack benchmark test used to rank systems in the Top 500. It held the top spot in June 2009 with 1.105 petaflops, but lost its place after being repartitioned. Jaguar, which was in second place in June with 1.059 petaflops, was upgraded with new processors and surged ahead to take the lead. It is based on the Cray XT5 Linux supercomputer platform, which uses AMD Opteron processors. Its total peak capability is 2.3 petaflops per second.

The No. 3 system is Kraken, at the National Institute for Computational Sciences at the University of Tennessee, which performs at 832 teraflops per second. This Cray XT5 supercomputer was ranked No. 6 in June, when it was rated at just 463 teraflops per second.

China's fastest supercomputer ever, the Tianhe-1 in the city of Tianjin, achieved 563 teraflops per second for the No. 5 ranking. It uses Intel Xeon processors with AMD GPUs (graphics processing units) as accelerators. Each node of the 71,680-core system has two Xeons attached to two AMD GPUs, according to the compilers of the Top 500 list. Tianhe-1 was built by the National University of Defense Technology for the National SuperComputer Center and is intended to provide high-performance computing services in northeastern China. Applications will include petroleum exploration and aircraft design.

The only other Top 10 system outside the US was Jugene, built by IBM at the Forschungszentrum Juelich in Germany, which was ranked No 4. U.S. computers dominated the Top 500 overall, making up 277 of the systems, with Europe accounting for 153 and Asia for 50. Just to make it onto the new Top 500 list, a computer needed to achieve at least 20 teraflops per second, up from 17.1 teraflops per second earlier this year.