Is windows 8 (download edition) attached to mobo?

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http://forums.anandtech.com – Hello, i'm looking at purchasing windows 8.1 by download from the Windows site, but i hope to upgrade in the near future. So is the windows 8 from the windows site an OEM version or retail version? in particular, is it attached to the mobo like Win 7 OEM and therefore invalidate my windows key for my next upgrade? Also, if i download from the windows site can i still do a clean install? They provide me with an ISO? or is it for upgrading only? Thanks for any clarification. (Hardware)