Computers based on the PlayStation's Cell processor dominate the world ranking for energy efficient supercomputers, according to the just-published Green500 list.

Joint first are two German computers which both hit 488.14Mflop/W using IBM BladeCenter QS22 clusters with PowerXCell 8i processors running at 3.2GHz.

The first is at IBM's own facility, and the second at Fraunhofer ITWM. They consume 22.76 and 18.97kW respectively, and are ranked 324th and 464th supercomputers in the world by the TOP500 list which ranks computers for number-crunching power.

Perhaps surprisingly, the most powerful computer in the world: Los Alamos Lab's 1Pflop Roadrunner, comes in third at 437.43Mflop/W and 2.3MW by virtue of its BladeCenter QS22/LS21 cluster of PowerXCell 8i at 3.2Ghz and 1.8GHz Opteron.

"Los Alamos National Laboratory recognised the performance opportunities of Cell, and accelerators in general, early on. That's what made a petaflop possible," said Andy White, deputy associate director at Los Alamos. "IBM is very energy conscious, and their design of the QS22 is the reason that three QS22-based systems, including our own Roadrunner supercomputer, are at the top of The Green500 list."

Green500 founder Wu Feng of Virginia Tech is pleased that Roadrunner scored so well on his list.

"This achievement provides evidence that energy efficiency is becoming as important as raw performance for modern supercomputers and that energy efficiency and performance can co-exist," he said. "For comparison, the last two supercomputers to top the TOP500 are now No. 43 and No. 499 on the Green500."

The next 12 Green500 entries are all IBM Blue Gene/P computers at between 371 and 357Mflop/W, and you have to get down to 17th place to find anything that IBM has not had a hand in - the 10th most powerful computer: SGI's 240Mflop/W Altix ICE 8200EX 3.0GHz Xeon quad core.

Nearly one in every three Green500 computers now achieves more than 100Mflop/W, compared with one in seven when the list was last compiled in February.

www.green500.org