The most powerful system on the list—IBM's Roadrunner—was also the most power efficient, delivering up to 488 Mflops/Watt. IBM's BlueGene/P system came in second at 376 Mflops/Watt.
"System like these based on accelerators and embedded processors are the most power efficient for the Linpack performance test," said Strohmaier.
Systems using Intel's Harpertown chips are catching up fast. They delivered power efficiency ranging from 221 to 240 MFlops/Watt in systems from IBM, Hewlett-Packard and SGI.
Strohmaier said he was surprised to find he "did not see as many multi-Megawatt systems as expected. Maybe our sample--we only have data for about half the systems--is skewed," he said. "You have to collect and analyze power data very carefully, otherwise you can easily draw misleading conclusions," he added.
Gigabit Ethernet continues to be the most widely used interconnect technology in the cluster architectures that dominate the Top 500 list. Gbit Ethernet appeared in 285 systems followed by Infiniband which was used in 120 systems.
IBM continued to be the leading vendor of systems on the list, including the top three computers. IBM made 210 systems of the Top 500 systems (42 percent), compared to Hewlett-Packard which ranked second with 183 systems (36.6 percent). Dell, SGI and Cray followed with 5.4 percent, 4.4 percent and 3.2 percent respectively.