I think some people are confused about the activation key when they really should be talking about the Product ID.
Your activation key is used to install your OS and the Product ID (the one displayed in "System") is the ID given to your PC after installation and subsequent activation by Microsoft.
As an aside...in my on-going saga to evaluate Win10, I just booted into it and my Windows Defender Real Time Protection was off and would not turn on until I rebooted Win10 again...then it returned to normal. Never had a problem with Win7.
So if Microsoft thinks that I'm going to find all the bugs and they are going to address them in the next 25 days, they are nuts... another reason why the 30-day limit to downgrade is grossly unfair and when you think about it, they are cutting their own throat because people are going to realize that 30 days is not enough and just ditch Win10.
90 days Microsoft...give us at least 90 days!
I'm surprised by the BS people are telling here. I have never had a retail license of Windows (Vista, 7, 8), always OEM licenses. I have reinstalled the various Windows versions countless times. And I have also changed my mainboards, graphics cards, cpus... many times. But so far I've never experienced troubles when it came to activate Windows. The worst thing that happened to me once was the need to talk to a MS support employee in order to get my Windows activated (I think it was Windows 8). OEM licenses that are available in online stores have never been bound to a single machine, they have always been transferable. Maybe they are bound to a single machine in theory (I don't read EULAs, it's not like I have a choice whether to agree or not) but in reality you can transfer them as you please or change the hardware whenever you feel like doing so.
Now what does that mean when it comes to Windows 10? Well we will have to see. And I think it's also kind of naive to assume MS is giving away Windows 10 licenses unconditionally. Of course they apply certain rules. But theoretical EULAs and reality are more than often two pair of shoes. A lot of paragraphs in EULAs are only there so you cannot enforce a right by taking the software developer/ distributor to court. It does not necessarily mean that MS handles such cases strictly like it's written in the EULA.
Well apart from the fact that you've got a retail license (the question is whether or not OEM licenses and upgraded Windows 10 licenses are transferable) you have to admit that eventually your Windows was activated. Some activation problems can occur at any time. But as long as MS support does not tell you to buy a new license instead of activating your current installation your license is still considered transferable by MS.
After upgrading from 8.1 to 10 I was being overwhelmed by issues (lockups on shutdown and returning from Sleep, Windows apps not working, etc.) the night before last I decided to rollback to 8.1 until I wanted to do a clean install. Well the rollback did not work. I could tell the OS was back as it would keep going back to the log in screen, but if I logged in all I got was a blank screen.
The 3 finger salute would still get me to task manager so I used RUN to open CMD (admin) and I ran the MediaCreationToolx64 to reinstall 10... This time things seem a little better other than not being able to log into the Win Store. It won't auto log in nor will it let me us the log in option. For now I am good with that because I really hate Windows apps, they just seem like really dumbed down attempts at a real program.
I just chatted with Windows Support and I told them what I did with the cloning and they had no issues whatsoever with me running Windows7 on the same machine as Windows 10. They also told me to just ignore the attempts it keeps making to upgrade my Windows 7 drive (the backup one).
If someone needs the text of the chat I can supply it.