That is what concerns me. A disk image of the current O/S is advisable. As soon as the Win8 installer popped up that it was irreversible I backed out and never gave it another chance to "thrill" me.

I still have a WIN 7 image of my old system just in case but looks like I will not need it.  Also, I had a triple boot system already set up and booting to my Win 7 test system, it still says that it is genuine.  Maybe what Sidroe is saying is that you can't create one after the fact.

StaringIntoNothing
I still have a WIN 7 image of my old system just in case but looks like I will not need it.  Also, I had a triple boot system already set up and booting to my Win 7 test system, it still says that it is genuine.  Maybe what Sidroe is saying is that you can't create one after the fact.

Hmm I'm booting 3 x Win 8.1 OS's on a single machine. If I update each one I wonder if I get a separate serial number for each.

The other concern is booting Linux, I heard rumours you can't disable secure boot, I have a feeling though it's just a rumour.

I just posted in the SONAR forum about my debacle this morning with the new Studio-Capture drivers. I don't know if any other products may have this same problem so it may be worth reading. 

Doktor Avalanche
Hmm I'm booting 3 x Win 8.1 OS's on a single machine. If I update each one I wonder if I get a separate serial number for each.

 
Interesting question to see if the updater handles that.  The way I would handle it is update one partition and if you like it, image it and install it on the other 2 already verified.  Microsoft uses hardware signature to verify the product key, so you can have as many as you want on the same machine with the same key.  I'm thinking updating all 3 will work because if you screw up, roll back and then update again, that will work on the same machine.  But imaging is the safest and fastest.  Easus ToDo free should work for you.

Yah, what if you want to download it and install it later (like, on another computer kind of later)? Do they let you save the image or is it "now or never"?
 

...wicked
Yah, what if you want to download it and install it later (like, on another computer kind of later)? Do they let you save the image or is it "now or never"?
 

 
You'vre got 12 months to do it.
http://m.winsupersite.com/windows-10/windows-10-upgrade-and-installation-frequently-asked-questions
 

...wicked
Yah, what if you want to download it and install it later (like, on another computer kind of later)? Do they let you save the image or is it "now or never"?

 
For sure, the file on this page gives you an ISO option to burn a DVD 
[link=https://www.microsoft.com/en-us/software-download/windows10]https://www.microsoft.com...are-download/windows10[/link]
 
I'll bet the installer that they have already downloaded to your computer does also, but have not tried it.  C:\$Windows.~WS\Sources\Windows\setup.exe