My Windows 8.1 drive. I removed my Win 8.1 SSD and put in a new SSD for Win 10. I was running Win 10 until I accidentally disconnected and reconnected power which fubarred Win 10. I pulled the Win 10 drive and reinserted the Win 8.1 drive so I could format the fubarred Win 10 disk. I have not changed or replaced any hardware but now the Win 8.1 install is showing as not activated which means if I decide to use it again I'll have to go through the automated phone routine. Not a big deal though. No idea at all why the install is showing as not activated. When I put the drive back in it went through a lengthy process of installing all the past updates that had been released while I was using Win 10 and they all installed without issues. I don't know what the process will be to upgrade to the final release of Win 10 though so I may have to reactivate my Win 8.1 install in order to upgrade to Win 10.