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I remember seeing a VMWare core dev speaking unofficially at a conference saying VT was actually slower and their software implementation was much faster.

Essentially this was just a quick way for MS to get virtualization in the OS pretty fast.

Edited 2009-05-07 19:14 UTC

This is how it breaks down:

AMD-V/VT-x: Generally slowest, but very stable, especially when the guest uses wierd processor features.

Software: Faster, not as stable. Wierd processor stuff can crash the guest.

AMD-V/VT-x + nested page tables: Faster than software, as stable as hardware. The first chips with AMD-V/VT-x didn't support NPT, but later ones.

And thank Intel as well, for basically disabling EFI on most PC boards... thank Microsoft, too, for insisting on using the cludgy BIOS calls in win9x for years, and for not even beginning to support EFI until Vista. There's a lot of blame to go around when it comes to the bios, the whole thing should've been reworked from the ground-up once its limitations became apparent years and years ago, but instead we just got hack after hack...
</rant>

Wow. Hardware virtualisation under hardware is slower under some circumstances than Software. In fact a hybrid solution is considered optimal. I have seen little of its security benefits. As for writing code to backport its interesting that companies who's entire infrastructure like say Sun sorry Oracle can do this, when they do not have the same vested interest in backward *binary* compatibility that Microsoft. As for smaller target of end-users being a good thing...its bizarroworld.

I look forward to Microsoft getting slapped from a Monopolistic and User standpoint. Personally I hope they continue these business decisions.

As for the bios switch comments well I never, as defending Microsoft, After Netscape; Wordperfect; IE6 etc etc them buggers have held back progress for years. Thank goodness we have other OS's with real virtualisation Support

Hardware VT being slower; that's news to me. Always good to learn something new.

I'm not defending Microsoft though, but seeing it from a software development perspective. They probably cobbled this together relatively quickly so the shortest code-path was the best option for them. There's many better ways to run XP in a VM, certainly; I just feel the hoo-ha over XPM's limited support is overblown.

Edited 2009-05-07 20:19 UTC

Yes, the BIOS disables the processor virtualization feature on most Intel and AMD platforms that could support the processor virtualization. The desk visit is for the IT person to change the setting in the BIOS setup program.

Remember the Blue Pill attack? The good people over at Invisible Things Lab published a virtualization hack that can take over a machine at a level where anything running in an OS would have a difficult task of detecting the attack.

In a quick reaction, the processor, BIOS, and system vendors decided to disable the feature by default. To enable it, the person holding the system has to hit DEL, F2, ESC, or whatever BIOS Setup key is defined and turn the feature on. Sorry.

If those pesky virus writers would go away, the vendors could ship systems that have all of the security features disabled.

This setting is done in legacy BIOSs, EFI BIOSs, and should be done in boot loaders / linux BIOSs. Don't forget the major purpose of the pre-OS firmware is to get the hardware ready for the OS. All of the pre-OS firmware has to support some of the older interfaces if you want to boot anything other than an Apple OS.