Valid/LEGAL Activation Codes

mozga628

Distinguished
May 9, 2012
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THE LONG VERSION:
I remember some time ago (Vista era) being told that a current (valid) MS activation code could be used to activate a previous (similar) product. at that time it was using a vista home key to activate win xp home. At that time i ended up upgraded to from vista to Win7, so I never found out if what I was told was correct, or (more importantly) still valid now.
I am looking at a dell 2in1 laptop, but it has win10... if I decide to get this laptop, I would be interested in UPGRADING the OS from win10 to win7. (yes, to me this would be an UPGRADE)
however, if this is not true (or can no longer be done), the additional expense of an OS is NOT something I want to absorb. so the answer I get here is rather important.
please and thank you for your help :)

THE SHORT VERSION:
Can a win10 key be used to activate win7?