I was referring to the fact that modern processors employ tricks like prefetch, pipelining, branch prediction, speculative execution, out-of-order execution...and so on...meaning that multiple instructions can be retired per clock. An simple instruction that multiplies by two (which may well be optimized to a left shift as Tom mentions) may be timed at 1 clock but might well take less than that. e.g. http://stackoverflow.com/questions/692718/how-to-find-cpu-cycle-for-an-assembly-instruction