Is it possible to install Windows 10 as the host OS and as one or several guest(s)?
With a single license of Windows 10, is it possible to install the OS at the same time as:
- The OS of the host machine (the non-virtual machine)
- The OS of one or several guest system(s)
In such scenario, the actual user of the Windows OS is a single person.
Solution 1:
No, you can't use your licensed copy of Windows 10 in a physical machine and a virtualized one at the same time.
Microsoft Windows 10 Use Terms
Take a look to this part:
a. License. The software is licensed, not sold. Under this agreement, we grant you the right to install and run one instance of the software on your device (the licensed device), for use by one person at a time, so long as you comply with all the terms of this agreement. Updating or upgrading from non-genuine software with software from Microsoft or authorized sources does not make your original version or the updated/upgraded version genuine, and in that situation, you do not have a license to use the software.
b. Device. In this agreement, “device” means a hardware system (whether physical or virtual) with an internal storage device capable of running the software. A hardware partition or blade is considered to be a device.
And here the explicit answer to your question:
d. Multi use scenarios. (iv) Use in a virtualized environment. This license allows you to install only one instance of the software for use on one device, whether that device is physical or virtual. If you want to use the software on more than one virtual device, you must obtain a separate license for each instance.
Solution 2:
This seems to depend on whether you are using a retail or volume license. As it is not clear from the question, I am going to cover both.
Microsoft have published an official guide (Licensing Windows desktop operating system for use with virtual machines) that suggests with Windows Software Assurance or Windows VDA Licensing you can run up to 4 copies of a licensed Windows desktop image concurrently in virtual machines.
The PDF brief postulates the following scenario:
An organization has a group of developers who need to test an application across multiple Windows images running in local virtual machine on PCs running Windows 10 Pro.
Licensing Solution:
The PC or the primary user of the PC needs active Windows Software Assurance, which permits running up to four virtual machines concurrently.
So in summary, if you have Windows Software Assurace / VDA then it appears that yes, you can run a single Windows license as a host and guest on the same machine.
However, if you are using the retail copy of Windows (without a Software Assurance or VDA addons) then I will refer you to @sahsanu's answer, which appears to be no.
I would strongly advise checking the terms of use that came with your Windows 10 license in either case.
Solution 3:
Windows 10 license terms state that one needs 1 license for each VM and 1 license for each physical machine (http://www.microsoft.com/en-us/Useterms/Retail/Windows/10/UseTerms_Retail_Windows_10_English.htm).
Prior to Windows 10 though, the restriction was that you could have up to 4 VM's on a licensed hardware machine sharing the license with the hardware machine (https://www.microsoft.com/en-us/Licensing/learn-more/brief-windows-virtual-machine.aspx).
Technically, all 5 machines are "eligible" for a free Win 10 upgrade. But it may not be the case that all 5 can be turned on at the same time, without violating the Win10 license, after the upgrade. I don't see any contradiction in saying that only one of the 4 VM's can be upgraded and used as a Win 10 machine though. But I am not a lawyer and MS has not (as far I was able to find) specified whether one could continue using 1 pre-win10 host and 3 unpgraded VM's if 1 VM were to be upgraded to Win10.