I recall that this was a little bit of a joke, a few year ago. Microsoft put it in a neat shell. - 7 or windows 7, 8 for windows 8 and now 10. Lord knows how they decided for Vista. but I might answer my own question. I cannot recall anything regarding the OS itself. Presumably, it would be subjected to the usual rule, ie. You cannot have the OS on more than one computer (Computer meaning Your Msphone, tablet..etc. But the wording was "Devices", however that is interpreted. You can remove devices from your online MS account.
I could stand corrected on this, as it is only a memory of a discussion some years ago.