If I decided to upgrade my parent's PC to Windows 10, can I download it to a USB stick or CD for installation later on? One thing which concerns me is, if in the future, the computer's hard drive needs to be wiped and the OS reinstalled in future, when the Internet is down or MS have stopped providing the Windows 10 upgrade for free. I have a genuine Windows 7 CD, which was purchased separately from the PC, not a shitty OEM install.
You have to actually perform the upgrade to get the license, but once you do, it's tied to the motherboard forever. MS will recognize your PC in the future if you ever have to reinstall (I think it's based on LAN MAC address plus some other things). Minor upgrades like a new CPU, hard drive, or video card don't seem to affect it. If you think you might want 10 in the future, you can do the upgrade on a spare hard drive, then put the original drive back in. It doesn't deactivate your old version of Windows.
This is what I did prior to the end of the free upgrade period a year after the release. I put a Windows 10 sysprep image on a spare disk and booted my Windows 7 machines with it. Did the activation, shut it down, and went back to the Windows 7 disks. I can now install and activate Windows 10 on these PC's and notebooks any time I want.
Microsoft has not made it hard to get Windows 10 install or upgrade ISO images. There will be a new one coming out in a month for the Windows 10 Creators Edition (the next W10 release).
The other thing you have to realise with the Windows ISO's is there really is only two versions - 32 bit and 64 bit. You can change the version you install by adding a tiny ei.cfg file to the install disk, and in that you can specify OEM or RETAIL installs, and also the type of installation - Home, Pro, etc.
You can do a clean install from a Windows upgrade ISO.
As it has been mentioned, the point of this thread is to show how you can still get your Windows 7 or 8.1 license and your hardware accepted by Microsoft as a valid licensed Windows 10 platform Once you have that, you can install and activate W10 whenever you want.