Grosch's law

Grosch's Law is the following observation about computer performance made by Herb Grosch in 1965:

There is a fundamental rule, which I modestly call Grosch's law, giving added economy only as the square root of the increase in speed -- that is, to do a calculation 10 times as cheaply you must do it 100 times as fast.

This "law is more commonly stated as

Computer performance increases as the square of the cost. If you want to do it twice as cheaply, you have to do it four times slower.