I doubt the usefulness of this method. wPrime simply starts one thread per core and probably sets the affinity mask so that each thread runs only on one dedicated core. The problem is that there are always loads of other threads running (other applications, services, OS itself), which are scheduled to execute on some available core; another active thread may therefore interrupt the second wPrime thread, then the 4th one, afterwards the 1st one etc. There has been quite a change to the thread scheduler in Win7, so this whole thing additionally depends upon your OS too. I did a 1024M test on Win7 and the order wasn't stable at all, no surprise there...