Two heterogeneous systems, based on NVIDIA’s Kepler K20 GPU accelerators, claim the top two positions and break through the three-billion floating-point operations per second (gigaflops or GFLOPS) per watt barrier. Eurora, located at Cineca, debuts at the top of the Green500 at 3.21 gigaflops/watt, followed closely by Aurora Tigon at 3.18 gigaflops/watt. The energy efficiency of these machines, manufactured by Eurotech, improves upon the previous greenest supercomputer in the world by nearly 30%. Two other heterogeneous systems, Beacon with an efficiency of 2.49 gigaflops/watt and SANAM with an efficiency of 2.35 gigaflops/watt, come in at numbers 3 and 4 on the Green500. The former is based on Intel Xeon Phi 5110P coprocessors while the latter is based on AMD FirePro S10000 GPUs.