Hello. This is my first post... A couple days ago, I tried a dual installation of 8.1 and 10 on my SP3Pro. 1- 8.1 bare metal restore using SurfacePro3_BMR_20_5.268.0.zip from MS ; activation and updates ok 2- upgraded to 10 using the iso downloaded from MS ; upgraded using setup.exe in explorer ; got it activated and updated (I deactivated KB3035583) 3- system partition shrink in order to get room for a second OS 4- downloaded Win 8.1 iso from MS. ("normal" iso as there is no SP3 Pro iso, only BRM archive = reset to factory) 5- deactivated secure boot 6- booted from usb-iso and installed 8.1 ; got it updated and activated ; no key needed In 8.1 Windows Update, I also deactivated firmware update (don't understand this firmware update, as WU already did it for W10... So I currently have win 8.1 and win 10 dual booting, all updated and activated. When I started, I was pretty sure it could'nt be done, as there is only one licence attached to the device ! But I have glitches : - if I reactivate secure boot in UEFI, there's no more boot menu, and it boots 8.1 only. - int 8.1 could'nt get Windows logo touch button to work. Could'nt get power button in start screen (I tried the registry tricks found with Google : failed) ; driver found on MS website shows an error in device manager (could'nt start, error 10) - in 8.1 could'nt get power and volume button to work (I have to power off using "start menu" Apart from this, everything seems to work fine Some thoughts ?