Assessing Trends in the Electrical Efficiency of Computation over Time

Information technology (IT) has captured the popular imagination, in part because of the tangible benefits IT brings, but also because the underlying technological trends proceed at easily measurable, remarkably predictable, and unusually rapid rates. The number of transistors on a chip has doubled more or less every two years for decades, a trend that is popularly (but often imprecisely) encapsulated as " Moore's law ". This article explores the relationship between the performance of computers and the electricity needed to deliver that performance. As shown in Figure ES-1, computations per kWh grew about as fast as performance for desktop computers starting in 1981, doubling every 1.5 years, a pace of change in computational efficiency comparable to that from 1946 to the present. Computations per kWh grew even more rapidly during the vacuum tube computing era and during the transition from tubes to transistors but more slowly during the era of discrete transistors. As expected, the transition from tubes to transistors shows a large jump in computations per kWh. In 1985, the physicist Richard Feynman identified a factor of one hundred billion (10 11) possible theoretical improvement in the electricity used per computation. Since that time computations per kWh have increased by less than five orders of magnitude, leaving significant headroom for continued improvements. The main trend driving towards increased performance and reduced costs, namely smaller transistor size, also tends to reduce power use, which explains why the industry has been able to improve computational performance and electrical efficiency at similar rates. If these trends continue (and we have every reason to believe they will for at least the next five to ten years), this research points towards continuing rapid reductions in the size and power use of mobile computing devices. INTRODUCTION February 14, 1946 was a pivotal day in human history. It was on that day that the U.S. War Department announced the existence of world's first general purpose electronic computer (Kennedy 1946). The computational engine of the Electronic Numerical Integrator and Computer (ENIAC) had no moving parts and used electrical pulses for its logical operations. Earlier computing devices relied on mechanical relays and possessed computational speeds three orders of magnitude slower than ENIAC. Moving electrons is inherently faster than moving atoms, and shifting to electronic digital computing began a march towards ever-greater and cheaper computational power that even to this day proceeds at easily measurable, remarkably predictable, and unusually …