DX12 is supposed to be much faster--closer to the hardware. I would have guessed that you'd be more interested in how it behaves with games.
Only problem is this: there are no games currently supporting DX12!
If you look around, people running DX11 and under games on Win 10 - they're running around the same.
The talk of a yearly fee for Win 10 seems to be false too. If I had a Win 7/8 PC, I'd probably jump on it. I won't bother my mom's PC with such a change. It'd only confuse her.
I think if more games requiring Win 10 (which would make it DX12 exclusive) would cause me to jump from my Win 7 gaming rig.
About my Win 7 PC - I got lots of stuff there installed. I'd probably want to 1st back-up lots of Game-Saves, actual game-folders (so I don't have to do re-downloads on BIG files), and whatnot on my Win 7 PC - just in case something completely goes wrong; or b/c I don't like that some App or game just won't work w/ Win 10.
If you do take Win 10 and upgrade - once done, you got 30 days to decide if you want to roll back to whatever you had before (i.e. Win 7, 8, 8.1). After that - supposedly, you can't roll back.
Or can I use her PC to download a Win-10 copy to install elsewhere?
You have to have Win 7, 8, or 8.1 to be able to take the free upgrade.
If you are offered the "Get Windows 10" icon (i.e. you'll have to do all the important Windows Updates before you can get that icon, more or less); turn on Windows updates to automatic; reserve the Win 10 download; wait for it notify you that you'll read to take the download; actually download the files on a PC supporting it; and then make a bootable ISO of the install.esd file.
More instructions here on how to do all of that ->
http://answers.microsoft.com/en-us/windows/wiki/windows_10-win_upgrade/how-to-create-a-bootable-iso-file-from-your/07590098-90a9-4c7e-b6fe-5ce1632daf4bFor ISO creating, I used Free ISO Creator ->
http://www.freeisoburner.com/That's as far as I went. Not going any further with it, at the moment. Will wait a little bit on Win 8.1 PC, before I do it there. Want to hear more impressions first + let M$ maybe iron out some things, before I take it. I don't have much to lose on my Win 8.1 laptop, namely b/c ain't much installed there and backing up won't be much of anything - since most of it's older games. Most of that stuff on my laptop, I basically already have on my Win 7 rig. If need be - I just port saves back and forth b/t the PC's (for any Non-Steam Cloud supported games).
What I do know from lots of reading + vid-watching:
You install Win 10.
Then at Microsoft activation time (to phone home to their servers), you will NEED to use your Win 7, 8, or 8.1 product key to activate Win 10.
If you don't know what it is (b/c a lot of new pre-installed Win 8 versions only usually actually give your Product ID, not your Product key). So, get a program to ID both Product ID + Product Key like BelArc Advisor:
http://www.belarc.com/free_download.html