The Fujitsu-built K Computer in Kobe, Japan, is the fastest supercomputer in the world, according to the Top500 List of Supercomputers, to be announced today.

For the first time since 2004, a supercomputer built in Japan can claim to be the fastest on earth.

That's according to the Top500 Supercomputing List, which is expected to be released today at the conference in Hamburg, Germany. The new leader, Japan's K Computer, makes its home in Kobe's RIKEN Advanced Institute for Computational Science. K Computer sped to the front of the class by achieving more than 8 quadrillion calculations per second (petaflop/s), which pushed it ahead of last November's winner, the Tianhe-1A at the National Supercomputing Center in Tianjin, China, which in the latest round achieved 2.6 petaflop/s.

K Computer was built by Fujitsu, and contains more than 80,000 CPUs with eight cores each. The last time Japan sat at the top of the supercomputing world was with NEC's Earth Simulator, which was dethroned in November 2004, after two years as fastest supercomputer.

In the top five, following Tianhe-1A, in ranked order, is the Department of Energy's Jaguar, housed at Oak Ridge National Laboratory, with 1.75 petaflop/s' China's Nebulae at the National Supercomputing Center in Shenzen, with 1.27 petaflop/s' and Tsubame 2.0 at the Tokyo Institute of Technology, with 1.19 petaflop/s.

The benchmark used to rank supercomputers is called the Linpack. It tests the performance of a system for solving a dense system of linear equations and is measured in calculations or floating point operations per second, hence flop/s. Not everyone in this field agrees it's the best possible way to compare machines, but it is one way.

This is a list that reorders itself fairly quickly, evidenced by Los Alamos National Laboratory's Roadrunner, the first system to break the petaflop barrier in June 2008, having fallen down to No. 10 on the list. The new Top500 list has 10 systems that have surpassed the petaflop barrier.

The most common application area of the 500 supercomputers on the list is research, with which 75, or 15 percent, of the systems are tasked. That's followed by 36 of the systems working on finance, 33 on service, 23 on the World Wide Web, and 20 on defense.

IBM has the most systems on the list, with 42 percent of them, followed by Hewlett-Packard with 31 percent, and Cray with 6 percent. The U.S. leads as the country that's home to the most supercomputers on the list with 256, China is next with 62, Germany has 30, the U.K. 27, Japan 26, and France 25.

For many more details about the 500 systems on the list, see Top500.org.