My proposal is to clone my 8.1 hard drive, disconnect it. upgrade the clone to windows 10, put my 8.1 hard drive back in the system, then boot either one i want. Does anyone know if this will work, or does windows 10 deactivate 8.1? If so, is there a workaround? I intend to leave windows 10 just sitting there until I need it and run 8.1 since I have it set up and running WMC perfectly. And please, don't answer with a diss of WMC. I don't want to waste any more time trying to install other dvr's that don't work or require hours of configuration.