Playing with Windows 10 yesterday... If you watched the old Adam's Family TV series, Lurch was known for a very distinctive grown -- that kinda sums up Friday's experience really well. :(
I hadn't read, hadn't seen the info I expected to be posted soon after 10's launch, so I started to play around myself to see how things work with upgrades, installations, & activation/deactivation. I started out with my Windows 7 Home Premium 64 bit VM. I'd read in a few places that if you install 10 fresh, it'll look for activated, qualifying copies of Windows [7/8.1], & automatically activate. At least for the win10 Home version, that appears to be false.
I added a new, empty VHD [Virtual Hard Disk] to the win7 HP 64 VM [Virtual Machine], & attached & booted to the win10 Home 64 bit ISO. During install you're given the opportunity to skip entering a key, so it will install fine, but when you're done it isn't activated.
OK, so scratch that, delete the new VHD with win10 on it, started over installing 10 as an upgrade from the ISO with win7 running. That time it activated as expected, I recorded the key using the utility from Nirsoft, & started experimenting. Using this VHD [with the newly upgraded 10 on it] in a new VM, making sure it used the same MAC address etc., & win10 was not activated. Cloning 10 to a new VHD, using the original VM, win10 was not activated. Note that's only my one time experience, & I was using VMs, so mileage may [or may not] vary.
While it's of course subject to change, unlike 7 you're not given a number to call when Windows deactivates -- in fact Googling on the phone number to activate 10 drew a blank. In a real life situation you could try the old number you can find on-line, but if that didn't work it looks like you'd have to remove your non-working key to get to that dialog & info. Hopefully the tools to do that in 7/8 still work. Microsoft's on-line help pages etc. all start with restoring/resetting your copy of 10 if/when it deactivates.
A side note... I wanted 7 back. Using a copy of the original VHD win7 ran [runs] fine, and it shows it's activated, though I've no idea what would happen if it were to deactivate so that we'd have to call Microsoft. So, with 7 on one VHD, & 10 on a copy of the same VHD, I set about making my 7 VM dual boot.
The 1st step was changing what's called a UUID that VirtualBox uses to identify the VHD -- that was easy using a utility called CloneVDI, which I wanted to run anyway to compact the VHD [meaning to get rid of all the free space making the single VHD file bigger]. BUT, Windows has it's own version of that ID that it uses -- if you have 2 drives with the same ID the 2nd will not boot, nor will it show up in the 1st copy of Windows. You can force that 1st copy of Windows to mount the 2nd drive [in Control Panel -> Admin Tools -> Computer Management], & then it will replace that ID with a new one. Problem is that Windows boot files [the files that are needed to actually start Windows] point to the old ID, so that has to be changed. EasyBCD will do it easily if Windows is set up to boot the old way, but if your system uses UEFI, in my experience you might have some problems [EasyBCD is dated 2012].
Windows has its own tools for working with &/or creating those boot files [BCDEdit & BCDBoot], & it's possible to work with the portion of the registry that stores that info, but the whole thing is really arcane & really a mess, far beyond anything that could be written in a forum post.
How this applies to real hardware -- not VMs... Unless some tricks or work-a-rounds show up on-line in the future, &/or unless Microsoft changes how things work now, it *looks like* the way to upgrade & keep your old OS is to 1st follow Microsoft's recommendation of upgrading your copy of 7/8.1 to Windows 10, to get your hardware entered into their win10 activation databases, then restore a backup of your older copy of Windows, & install 10 fresh to another partition -- that should create the boot menu for you. It *may* work to install 10 fresh to another hard drive, but my initial test in V/Box suggest no.
Hard drives fail & have to be replaced, so I imagine MS will have to make some provision for different [new] drives with their activation stuff, but right now with 10 fresh & people trying to get extra licenses free, I can see them being maybe over restrictive, & can only hope that changes later on.
Now, another problem I've had to deal with is backup software... I bought one of the cheaper win8.1 tablets -- these use pure 32 bit UEFI, & the only thing that will create a boot stick that works seems to be Macrium Reflect. You can create a bootable USB stick with AOMEI Backupper, then copy [replace] the boot.wim file to a Macrium Reflect USB stick, & that will run. Being pure 32 bit UEFI, with a GPT drive having 4 partitions, I had poor luck with Paragon's v. 14 software -- a restored backup [to a VHD] would not run, but using Macrium Reflect v.5 it would.
Fastforward to my playing with 10 in a VM... I wanted to clone the drive to a new VHD. Neither Macrium Reflect 6 nor the latest version of AOMEI Backupper created a clone that would start & run. If win10 was the only copy of Windows on my PC, not having known good backup software would Really worry me. I do intend to test out win10's built-in backup, but wanted to get that info posted today to warn folks.