Q How quickly is CPU performance improving?

A Single core performance has improved by an average of 30% per year for the last five years.

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Back the late nineties the rate of increase in cpu horsepower was phenomenal, every two years processor throughput was doubling. As clock speeds reached 3 and then 4 GHz the emphasis shifted from linear single processor speed to multi-threaded performance. There has been a relatively slow and predictable improvement in performance over the last five years and there is no longer the need to upgrade a CPU more than once every three years. In terms of single core performance, a reasonable proxy for real world performance, the late 2007 Core2 Duo E6550 scored 881 points on PassMark-S vs 2080 points achieved by the Mid 2012 Core i7 3770K, roughly a 140% increase in performance over the last five years or roughly a thirty percent improvement per year.