Calculate True cpu speed.?

A 3 Ghz CPU with 4 cores isn't the same thing as a single 12 Ghz processor. For instance, many programs are not able to use all 4 cores efficiently (the program would need to be properly parallelized to do so). Also, if the cores share cache memory and/or other components, they could block each other or cause other issues. You could use benchmarks to test speed, but CPUs with X cores can't be exactly compared to a single-core CPU running at higher speeds. They both have their own advantages and disadvantages.