Q: How do I enable processor compatibility on Windows Server 2012 Hyper-V for earlier, legacy OSs?
A: In the early versions of Hyper-V, there was the option for processors to support older, legacy operating systems such as Windows NT 4.0.
This configuration hid additional processor information from the virtual machine (VM) such as logical processor to cache mapping, which otherwise would cause the earlier OSs to crash. The ability to hide this is still available but it must be configured with Windows PowerShell as follows:
Set-VMProcessor -CompatibilityForOlderOperatingSystemsEnabled $true