My understanding of Windows10 is that the *free* (
) upgrade applies to the Win7/8 system in use ie if you have 3 Win7 systems then you need to perform the upgrade download and install on each system.
What I found, was a selection of three ISO downloads. One that is 32 bit, one that is 64 bit, and a third that is both. The update path is from win7, or Win 8.1 (you must update Win 8 to 8.1, apparently). The update will migrate a 32 bit system to a 32 bit Win 10, and a 64 bit system to a 64 bit Win 10. These ISO files are made for those who maintain multiple systems (download once, update many systems), but they are also recommended for those who are having trouble getting the Win 10 update in the normal way (I kept asking, they kept saying I would get it, but two months went by with no results, so I went looking further). FWIW, my nephew got Win 10 installed, without asking, and he couldn't stop it once it got going. He had to back out, but, as I understand it, his machine is now registered as having Win 10, so he should be able to install again, at any time (even after the cut off date). He does, of course, need to start with Win 7 installed, since that was his update path. Of course, the license is tied to the machine. if the machine changes, it is no longer licensed.
I did install Win 10 on my Lenovo ThinkPad L530 (using the 64 bit DVD). I must say that the update looked pretty good, initially, however, trying to actually use it was an adventure in frustration. No virus ever caused that many problems. They give you 30 days to be able to use Win 10 to revert back to the previous version. From what I hear, Win 10 is better than Win 8.1, but IMO it is certainly not as good as Win 7. Good thing I made a complete backup, because the reversion program missed a few things. That should mean that I can update again, at any time. I intend to backup my other machines, install Win 10, then back them out (restore if necessary). If that doesn't work, I really haven't lost much, because I can still use Win 7, when I need it (not much).
I should note, that I never did create a logon ID for the MS login thing, which may have something to do with my troubles with Win 10. Of course, that also appears to have prevented it from storing all of my information on the MS servers, where you need to authorize them to look through it so they can send you the appropriate advertizing. My windows systems have very little information on them, but windows users are giving away their whole life history, and most of them don't even know it.
installing from the DVD requires the input of a Licence Key.
True, IF you need to do a clean install. It will update Win 7, or Win 8.1, without a license key. It then reports to MS that your machine has whatever updated version you used, and records your machine information for future reference. Apparently, they don't even care if the Win 7, or 8.1, is a legal install, although I am not sure that I would want to test that.
I think it is not legal to install to a VM without doing a clean install, which would require a purchased key. As I understand it, if Win 7 will run, so will Win 10 (but I never tried).