VMX vs VT-x Mode?

I started getting the following message recently when I start a VM (i.e. Windows XP Pro):

The virtual machine being started is going to switch VMX mode on. Parallels Workstation has detected that VMX mode is already activated by another running application. If that application will stop VMX, the virtual machine may behave unpredictably.
Click Ok to start the virtual machine with VMX support, or click Cancel and edit VT-x settings.

I don't remember getting this message when I first installed WinXP. What does this mean? Have I lost VT-x support in favor of VMX? How do I restore the VT-x capability?

Thanks,
David

 

VMX and VT are the same thing.

Try rebooting to see if this problem goes away.

 

Could you provide a little more detail about the difference. My impression is that VT-x was the virtualization technology in the new Intel Core Duo chips that allows Parallels (or other software) to run other OS'es in a VM at near native speed. I thought I read somewhere that VMX was Parallels implementation of virtualization if VT-x is not supported on the CPU on which Parallels is installed. It seems VMX would be "slower" than VT-x. I could be totally off here so please clarify the difference for me.

Thanks,
David

 

VMX = Intel Virtual Machine eXtensions, the instructions that represent VT
VT-x = hardware virtualization via Intel Virtualization Technology (VT)

In this context, VMX and VT-x are the same thing. VMX is not software virtualization.

 

Thanks for the quick response and explanation. So, to follow-up a little:

1) I assume then that enabling VMX is a "good" thing
2) What other applications might be activating VMX mode causing the original message?

David

 

1) Yes, having VMX/VT-x enabled is a good thing.

2) It's probably no other application...it's likely that there's some artifact of Parallels that is still holding onto it. I've seen this message a couple of times myself during testing, and rebooting has always cleared the condition.

 

Is it possible that Rosetta's emulation layer could be hooked into a VT-x ring to protect the rest of the system? This is wild speculation as I have no idea regarding the architecture of Rosetta.

Regards,

Phil