short story: I was having performance issues in BC2 back when it was new, noticed in cpu monitor that I was only showing two cores, didn't think much of it. Couple weeks later I stumble upon a thread talking about this command. Mine was unchecked (which is supposed to cause windows to use all cores). I checked it, rebooted. Unchecked it again, rebooted. Checked my cpu monitor again and BOOM four cores showing.
If you're having issues with core(s) not showing up, might wanna try this.
I am jaded. I am cynical.