5.18 win 7 host win 8.1 guest 0x000000c4

[michaln]

[*]Is it only Win8.x that requires it, or anything > Win8? Like Win10 for example.

As far as we know, everything required by Windows 8.1 is also required by Windows 10. However, not everything required by Windows 8.1 is required by Windows 8, and not everything required by Windows 8 is required by Windows 7.

The hard part is figuring out what the exact CPU requirements for Windows 8.1 (or Windows 10) are, because Microsoft does a really shoddy job of documenting that. It is well known that some systems that run Windows 8 won't run Windows 8.1, but the precise list of required features for 32-bit and 64-bit versions is hard to find, if it even exists.

I know that CMPXCHG16B is required by 64-bit Windows 8.1/10, but not Windows 8 and earlier. I believe NX is required by Windows 8 and later but not Windows 7. SSE2 is also required, but every CPU which supports NX also supports SSE2 according to Microsoft, so that is not an issue in practice because it can't be disabled.

Is VirtualBox warning itself here?

Yes. Other than spamming VBox.log and raising unnecessary questions, it is harmless.

[socratis]

Great, thanks for the clarification!

[J.Dow]

Here's the key clue from the log: "CPUM: WARNING! Can't turn on NX/XD when the host doesn't support it!". We should really not even allow the VM to start in that case, because Windows 8.1 requires it (Windows 7 does not). NX/XD is the 'No-eXecute'/'eXecute Disable' bit which prevents code to be executed from certain pages.

Thank you very much. That turned the trick.

{^_^}