I have used MTK, KMSpico, and Activate8.1x64.exe to activate win 8.1. I like Activate8.1x64.exe because it does not appear to install a kms system on the PC and does not have to re-activate after 180 days. I am assuming that is why its called "Win 8 permanent activation". What is the difference, if any, between these activators? Thanks, Mark.