When news of Windows 7's "XP Mode" came out recently, there was much rejoicing among those who were concerned about legacy support in Microsoft's upcoming OS. But now we learn that Microsoft and Intel have contrived to make XPM unavailable to many Intel users.

We knew it was too good to be true! Just when we expected Microsoft to make major inroads to loosen the grasp of reluctant users to their Windows XP OS came the news that Windows XP Mode for Windows 7 will only run on virtualization capable CPU's. "This new wrinkle was the discovery that Windows 7's recently announced XP Mode would only work on processors that supported either Intel's VT or AMD's AMD-V. The vast majority of AMD's lineup, except for Sempron, has AMD-V and will work, but the Intel situation is much more complicated, and in some ways, worse."

In a nutshell, Intel's VT-x and AMD's AMD-V work by introducing a set of instructions that make x86 fully virtualizable without the use of binary translation. This was originally supposed to have speed advantages, though when VT first made its debut the transitions in and out of the hypervisor were slow enough that BT arguably still had the edge. But this hasn't been true for some time, and now VT is the way to go if you're rolling out a new x86-based virtualization package, like Microsoft's hyper-V or Virtual Iron's software.

But VirtualPC, the virtualization package that Microsoft bought and on which XPM is based, is a binary translation solution, just like VMware. So the question then becomes, why did Microsoft mandate VT support for XPM?

Intel uses VT for product segmentation, regarding it as a high-end feature and charging more for it. This is very annoying if, like me, you believe that everyone will shortly be running a hypervisor on every device that isn't a mobile phone (and eventually phones will get them too, if VMware has its way). But as annoying as this approach to product segmentation is, it makes a certain amount of sense given Intel's situation in the post-clockspeed era.

As you can see and we had mentioned in a previous article, quite a few users won't be able to use XPM when Windows 7 comes out, especially on the corporate desktop, where many companies have opted for cheaper, non-VT parts. This is dissapointing as we had finally begun to think that this just might be the practical solution to reluctant clients and users who were hesitant to change their XP desktops for fears of lack of drivers (solved with Windows 7), stability (solved with windows 7), and not being able to run legacy applications (almost solved, two out of three isn't bad).

We hope that we have more clarity on this as windows 7's release date approaches and that Microsoft will change it's course on this requirement, Intel can help as well going forward. C'mon Redmond, you guys can really score big with your users if you make this XP Mode as simple as it sounded when it was first announced.

let's keep our fingers crossed!