In this special guest post, Axel Huebl looks at the TOP500 and HPCG with an eye on power efficiency trends to watch on the road to Exascale. “This post will focus one efficiency, in terms of performance per Watt, simply because system power envelope is a major constrain for upcoming Exascale systems. With the great numbers from TOP500, we try to extend theoretical estimates from theoretical Flop/Ws of individual compute hardware to system scale.”