[Mashiro]

If you really want to stick with your current system, I would suggest to convert it to a VHD VM then convert it to a QEMU disk image (qcow2) which you would then use in KVM. It's a bit advanced stuff but doabale with the right assistance/guidelines.

@fChk

Your reply seems a bit short sighted with all due respect. Please don't be offended by this comment of mine. I will explain why below so you can understand what I mean. I can't even really blame you because I'm also rather short sighted or blind to some things because I do them often or have a lot of experience with them. I keep catching myself doing it often enough, too.

You cannot expect someone who has been using Windows all their life to switch to Linux and use KVM to virtualize their old Windows system to be able to still use it in cases when they might still need it. Especially here you can't just throw this out into the open. From my time here, with high confidence, I can say that only a very small percentage of users would be able to do what you suggest (which includes you, me and a few others). I'm helping out here a lot and often see that even Linux basics aren't a thing for many users. And when you expect people to read and follow guides for such rather complex things (as you said it yourself "It's a bit advanced stuff...") I have another bad news for you. Anyway. I'm just trying to explain that your advice is not good for people who want to switch from Linux to Windows and still retain their old Windows system in a usable way. It is the right direction but not the right instruction for the audience that mostly visits this site and posts here (or rather said the experience level needed is too high for most).

A user that wants to switch will probably use a common Linux distribution with a desktop enviroment and a window manager (or lets simply say a GUI). A GUI is probably the most important for Windows users switching to Linux. Now we both know that people who post here also certainly have CLI experience as they do use Linux in CLI (mostly) on their VPSs from here. That's good but in most cases to come as close to Windows as possible I think users will be using GUI tools like the software and package manager and etc. So my advice would be rather the following (see below). I think it is easy and user friendly for people who just switched to Linux.

On the old Windows system I would suggest to use Disk2vhd by Windows Sysinternals to make a one to one copy of the Windows system and all the software, files and etc... in form of a virtual HDD file that can be used with a lot of virtualization software types. It's a neat little GUI tool for Windows. You start it. Select which drives you want to make a VHD copy of and then you specify a path were to save the VHD files. Hit button and let it do its magic. During the process I of course wouldn't recommend to do anything else that would make changes to the drives. That's where I'm with your idea still.

Now comes the part I would approach different. Lets say that the user now has already installed a Linux distribution of their choice and is basically using it already. I would launch the package manager, search for Virtualbox and install it. This way you will get a nice virtualization software with a GUI and most even know about it already and have used it. It's easy to use and follow compared to setting up and configuring KVM and KVM machines via the command line. After its installed they can launch it, create a new VM for their old Windows system following the wizard and then they can select the VHD files of their old system when they're at the part where they can configure the disk of the VM. And in the advanced settings they can even change the Virt type to KVM. Which I would suggest to do if the hardware supports hardware virtualization. KVM is just so much better for close to real hardware emulation.

I know this is much easier and faster to do than using KVM purely because I have already in the past used pure KVM and also have use VMWare, Virtualbox and Hyper-V. Out of all of them the fastest way is always using a GUI application if you're on a OS with a GUI already and load up existing VHD files. I did/do this at work all the time. Especially now when we're moving a lot of servers that are physcial to a different data center where they will be running as a VM. We create a VHD of them and send it over a symmetric 1 Gbit/s connection inside our MPLS fibre Intranet network to the data center. A little later the server is up and running as a VM on their cluster (they use Nutanix though). I even did this with my old computer during transition time as we all know that it is hard to build up a new system when your old computer already has all apps, all configurations and etc. Worked like a charm.

That's it. If I missed something feel free to point it out. As far as I'm aware from doing it multiple times the process doesn't require any bit more knowledge than what most people here already have. Even if it does the guides and information would be easier to comprehend and follow.