With windows 7 OEM the license is tied to the first motherboard it's installed on.
With Windows 8.1 you can move it to another build when you are done with this one , but only one computer at a time.
With Windows 8.1 you can change all the hardware you want including the motherboard.
and it could certainly be used if you changed the motherboard.Can be transferred to new hardware, if removed from the prior PC.
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