I'm using an *Intel(R) Core(TM) i5-4200U CPU @ 1.60GHz* and wondering why the multiplication of 64 bit numbers is slower than that of 32 bit numbers. I've done a test run in C and it turns out it needs twice as much time.

I expected it to need the same amount of time since the CPU works with native 64 bit registers and it shouldn't matter how wide the numbers are (as long as they fit into a 64 bit register).

Can someone explain this?