Activation is not registered in the BIOS, only (a) in Windows, and (b) with Microsoft.
So if you have 2 paid license codes, you can use both OS'es. But if you UPGRADE 8.1 to 10 in stead of doing a new install of 10 as a dual boot, that invalidates the 8.1 license and you'll have to buy a new one most likely. Anyway, Microsoft can tell; you have to contact them anyway if the reactivation isn't automatic.
Kees
I have installed a win 10 on my win8.1 computer on differant partition.
After few days win 8.1 say that my activation key is wrong and I need to reactivate.
I'm affraid that reactivation will only works until my next win 10 upgrade ( probably reseting key in the bios )
What can I do ?

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