Okay obviously as we all know, OEM is meant to mean, registered to one machine and not tansferable to subsequent ones. Quite how I'm not sure but I think it's the MB and info on that is picked up by Windows and sent during registration. Correct ? Anyway, that's not so much what I need to ask. Background : I'm trying to retain for use an old machine built in 2007 but with a very good spec, for games from the XP era that have just sat on a shelf. I'm not 100% sure it will work out. But I know someone for whom needs are simpler, don't involve games etc and also needs Win 7. The reason for both of us wanting to make the move soon, is the ending of support for XP and therefore increasing online vulnerabiulity. SO TO THE QUESTION : If it doesn't work out for me and I don't immediately register the copy, would I be able to let the other guy try and then go ahead with registration for him ? Or, would there be some kind of stamp of MY machine left in Win 7 despite my not having registered it ? In other words, does it have to be registered before it gathers and retains information about a system installed on ? This is not a cheat in spirit, because there actually is only going to be one user of it on one machine. Either mine if it works fine, or his if I'm not satisfied. And if neither satisfied, then binned. I'm just concerned that Microsoft might detect a breach in strict terms if, even without registering, it picks up that an attempt had been made to work on another machine first, thereby rendering it useless for the other guy ( and embarassing ). Just to clarify, if I'm happy with 7 it will mean eventually two copies bought and each registered to one machine, as intended by Microsoft.