My friend will be building a hackintosh on Sunday, which leaves his old computer to sit in a lonely corner, which is good for me because he has agreed to let me have his old processor + motherboard in exchange for mine. (His being a Phenom II X4 965, mine being a Phenom II X4 840)
My question is, would we need to format our hard drives and re-install windows once we swamp motherboards and CPUs?
I planned on reformatting mine anyway, but he doesn't really want to reformat it.
(I already posted this on another board, but hope get more insight)
Even with OEM, you might not need to re-install. I've done some changes with motherboards and CPUs on OEM machines without needing to re-install (even though it is supposed to be tied to the motherboard). The CPUs shouldn't be an issue for that, the motherboard is usually the deciding factor. You can try exchanging the board (regardless of whether you have OEM or retail Windows) and see if it works. If not, then you can also try putting in the old board and installing drivers for the new one, shutting down, and try upgrading the board again. If it works, great, if not, then a re-install is probably necessary.
However, I'd recommend a re-install even if it works without one. It's good to re-install every few years to clear out any junk in the registry and such that can slow the computer down or cause increased instability over time. Exchanging motherboards is a great reason to re-install.
Hardware incompatibilities shouldn't be a problem, but Windows can be finicky. I make no guarantee that you'd be able to exchange the boards without re-installing Windows and I recommend that you re-install if you can even if you don't need to. If you do re-install, then since both machines would use an OEM copy of Windows, you might need to contact MS about it if you have problems, but there probably won't be any.