Figure from ROBOT, Moravec, Oxford, 1998, Chapter 3: Power and Presence, page 60
Power/cost of 150 computers from 1900 to 1997, rising 1000x every 20, now 10, years

Faster than exponential growth in computing power
The number of MIPS in $1,000 of computer from 1900 to the present. Steady improvements in mechanical and electromechanical calculators before World War II had increased the speed of calculation a thousandfold over manual methods from 1900 to 1940. The pace quickened with the appearance of electronic computers during the war, and 1940 to 1980 saw a millionfold increase. Since then the pace has been even quicker, a pace that would make humanlike robots possible before the middle of the next century. The vertical scale is logarithmic; the major divisions represent thousandfold increases in computer performance. Exponential growth would show as a straight line, the upward curve indicates faster than exponential growth, an accelerating rate of innovation. The reduced spread of the data in the 1990s is probably the result of intensified competition: underperforming machines are more rapidly squeezed out.

Richard Wallace's 1994 New York University computer architecture class, especially students Mohammed Kadir, Irina Pirotskaya, Alexandr Shenker, and Scott Sterling provided 1987 to 1994 data for this graph.

Numerical Data for the Graph