What is the difference between the OEM and retail version of windows?
In terms of functionality, nothing of any substance.
In terms of licensing, retail copies are far less ****** in terms of switching motherboards and ****.
So just some little things no one cares about right?
If you think you may be swapping motherboards at some point or wanting to switch your Windows install to another system, get the retail version. As stated, OEM is tied to the hardware it is installed on the first time (laptops come with OEM, for example)
You can install the retail version on as many PCs as you want (one at a time) while the OEM version gets tied to the PC (motherboard) of the first PC it is installed.
Microsoft OEM Software Licensing: Rules & Restrictions:
OEM Software may NOT be transferred to another machine. Even if the original laptop, PC or Server is no longer in use, or if the software is removed from the original hardware, OEM licenses are tied to the device on which the software is first installed...