Are there tools to find out if there is an OEM key embedded in my computer's Bios/EFI ?
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Use SLMGR to get some information.
cmdand press ENTER.
SLMGR /DLVand press ENTER.
A dialog similar to the following should display license information:
See 3 ways to check whether your Windows is activated and genuine for more details, and TechJourney for more on SLMGR.