dodger46 :
The only 'restriction' is Activation. If you change Motherboards or install to a different Laptop, you have to Activate Windows afresh, simply because you may have tried to install to more than one PC, which, of course, breaks the Licence conditions. This can easily be achieved automatically over the telephone, and is straightforward provided you answer 'One' to the number of Computers on which Windows is installed...
With Windows 8 and 8.1, changing hardware is no longer a concern. You can change whatever you like, up to and including a whole different PC.
Yes, it might need reactivation,
but changing hardware no longer breaks any license agreement.
From the Windows 8.1 license:
"
Can I transfer the software to another computer or user? You may transfer the software to another computer that belongs to you. You may also transfer the software (together with the license) to a computer owned by someone else if a) you are the first licensed user of the software and b) the new user agrees to the terms of this agreement. "
Same PC, new PC, new hardware...whatever.
Only one at a time, but the hardware does not matter anymore.