Welcome to the Green500 list! The purpose of this list is to provide a ranking of the most energy-efficient supercomputers in the world and serve as a complementary view to the TOP500.

For decades now, the notion of "performance" has been synonymous with "speed" (as measured in FLOPS, short for floating-point operations per second). This particular focus has led to the emergence of supercomputers that consume egregious amounts of electrical power and produce so much heat that extravagant cooling facilities must be constructed to ensure proper operation. In addition, the emphasis on speed as the performance metric has caused other performance metrics to be largely ignored, e.g., reliability, availability, and usability. As a consequence, all of the above has led to an extraordinary increase in the total cost of ownership (TCO) of a supercomputer.

Despite the importance of the TOP500 list, we argue that the list makes it much more difficult for the high-end computing community to focus on performance metrics other than speed. Therefore, to raise awareness to other performance metrics of interest, e.g., performance per watt and energy efficiency for improved reliability, we propose a complementary list to the TOP500 - the Green500 list.