With a release candidate of Windows 7 poised at the threshold, Microsoft revealed a last-minute surprise last week: Business versions of Windows 7 will have a downloadable add-on that offers a high-performance virtualized copy of Windows XP. If compatibility issues with Windows 7 (or Vista) are holding back upgraders, many analysts and bloggers reason that this feature should eliminate one more barrier to upgrading. If only it were that simple!The basic goal of "XP Mode" is laudable, and it seems like the best technical way for Windows 7 to provide full backwards compatibility without having to carry around a lot of cruft. Users that need Windows 7 to work just like XP don't need to compromise; they simply run a real copy of Windows XP on Windows 7. The question is whether users who need that level of compatibility have (or will buy) the hardware to use it.

Not every processor has the features to use XP Mode; many processors sold today can't run it. If you have an existing system, you can download the SecureAble utility from Steve Gibson. It will detect whether the processor supports hardware virtualization, the feature needed by XP Mode. If you're buying a new processor from a retailer like NewEgg, their product information indicates "Virtualization Technology Support" in the listing. It may not be quite as easy to tell the score for OEM computers; you'll need to look up the exact processor model and check the AMD or Intel site if the OEM doesn't say anything about virtualization support.

I wonder how many (and how quickly) businesses will upgrade to Windows 7 if Windows XP compatibility is a high priority. Since many current processors don't have the virtualization support required for XP Mode, simply upgrading an existing PC to Windows 7 won't solve the problem for many (if not most) businesses. Updating the operating system on an existing older PC has its own set of challenges anyway, especially since Windows 7 won't support an upgrade from Windows XP. If a business wants Windows 7 but also needs XP Mode, the most practical course is to buy a new PC with a new processor that supports hardware virtualization.

Finally, there is the problem of Windows XP dependency. Microsoft's current timeline has XP reaching the end of its life in 2014; that's the point at which Microsoft won't offer security patches for it anymore. XP Mode in Windows 7 will continue that dependency for several more years; Microsoft will be sanctioning, perhaps even encouraging, its use. That will most likely lead to a last-minute reprieve for XP support come 2014, even if Windows 7 is wildly popular.