Virginia Tech released the inaugural Green500 List (www.green500.org) at the Supercomputing 2007 (SC|07) conference in Reno. “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,” said Wu Feng, associate professor in the Departments of Computer Science and Electrical and Computer Engineering at Virginia Tech. All systems on the Green500 are ranked by MFLOPS/Watt (million floating-point operations per second per watt). The “MFLOPS” numerator is the reported LINPACK sustained (Rmax) value recorded by the Top500 List. (LINPACK is a linear algebra software package used to create equations to challenge computers.) The “Watts” denominator is either a direct measurement of the system running the LINPACK benchmark at Rmax load or a peak power estimate based upon machine specifications. For now, systems must first place in the current Top500 List in order to be considered for the Green500. Of the Top500 machines, more than 200 machines directly reported their measured power for the Green500 List. In cases where measured power was not provided, the Green500 List used peak power, as estimated by the Green500 team, based on the best available specifications for the systems in the Top500 List. The November 2007 Green500 List is a combined ranking of all 500 machines based on the best (i.e., highest) MFLOPS/Watt rating available from either direct measurements or peak power estimations. Because peak power numbers do not necessarily reflect power consumption under load, the Green500 team specifically discourages direct comparisons of measured and peak values in the current Green500. “As this list is the first attempt of its kind, the rankings are open to interpretation by the media, associated vendors, and the general community,” said Kirk Cameron, associate professor of computer science at Virginia Tech. “The Green500 team encourages fair use of the list rankings to promote energy efficiency in high-performance systems. We discourage use of the list to disparage a particular vendor, system, or user,” he concluded. The list itself and the methodology used to rank the systems are works-in-progress, Feng said, adding that this will evolve over time to ensure accuracy and more closely reflect energy efficiency in the fast-paced, ever-changing, high-performance community.