Quantitative performance analysis is the foundation for computer system design and innovation. In their classic paper, Emer and Clark noted that ‘‘a lack of detailed timing information impairs efforts to improve performance.’’ They pioneered the quantitative approach by characterizing instruction mix and cycles per instruction on timesharing workloads. Emer and Clark surprised expert readers by demonstrating a gap between the theoretical 1 million instructions per second (MIPS) peak of the VAX-11/780 and the 0.5 MIPS it delivered on real workloads. Hardware and software researchers in industry and academia now use and have extended this principled performance analysis methodology. Our research applies this quantitative approach to measured power and energy.