The Green500 List debuted in November 2007 and ushered in a new era of energy-efficient supercomputing. The Green500 List is intended to serve as a ranking of the most energy-efficient supercomputers in the world and as a complementary view to the Top500 List. The second edition was released in February 2008. And now, the third edition of the Green500 List www.green500.org arrives on the heels of the recent International Supercomputing Conference, arguably one of the "greenest" conferences to date. Wu Feng, a member of both the computer science and the electrical and computer engineering departments in Virginia Tech's College of Engineering and founder of the Green500, said there were several "notable highlights from this edition of the list." First, the first sustained petaflop supercomputer, Roadrunner developed by the U.S. Department of Energy Los Alamos National Laboratory, exhibits extraordinary energy efficiency. Roadrunner, the top-ranked supercomputer in the TOP500, is ranked third on the Green500. "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. For comparison, the last two supercomputers to top the TOP500 are now No. 43 and No. 499 on the Green500," Feng explained. "Los Alamos National Laboratory recognized the performance opportunities of Cell, and accelerators in general, early on. That's what made a petaflop possible. 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," said Andy White, deputy associate director at Los Alamos National Laboratory. "The Roadrunner supercomputer is akin to having the fastest Formula One race car in the world but with the fuel efficiency of a Toyota Prius," Feng added. Second, nearly one in every three supercomputers on the Green500 List now achieves more than 100 megaflops/watt (where megaflops stands for millions of floating-point operations per second), whereas in the previous edition of the Green500, only one in every seven supercomputers did. On a related note, the top-ranked Green500 supercomputer improved by 131 megaflops/watt since November 2007 whereas the bottom-ranked Green500 supercomputer only improved by 0.39 megaflops/watt for a difference of three orders of magnitude in energy efficiency. Third, exactly three supercomputers surpassed the 400 megaflops/watt milestone for the first time. All three machines are based on IBM's BladeCenter QS22 chassis with the Cell processor, the processor that also serves as the basis for the Sony PlayStation 3. Based on feedback from e-mails to the Green500 and from a recent Birds-of-a-Feather session at the International Supercomputing Conference, the Green500 will evolve to be more inclusive for all high-end computing stakeholders. Additional developments will be posted on the Green500 web site. Feng said, "The organizers of the Green500 welcome further analysis of the data for additional takeaways and further encourage raising awareness in energy-efficient or green supercomputing. We also encourage fair use of the list rankings to promote energy efficiency in high-end computing systems and discourage use of the list to disparage."