For over a year now, the Microsoft mantra on Windows 7 has been very consistent: The OS will utilize the same software and hardware compatibility model of its predecessor, thus ensuring that customers won't have to go through another painful cycle of testing, worrying, and putting off deployments. Microsoft explained, again and again, that the technical underpinnings of the OS would be so similar to that of Windows Vista that no one would need to worry about compatibility this time around. What was making Windows 7 a major release, we were told, was the surface stuff, all the UI and user experience changes.

Well, hold on to your hats. It seems the Windows 7 compatibility story has yet to be told.

Last week, Microsoft finally admitted that the company has been secretly working to improve application compatibility in Windows 7. This change means that Windows 7 will actually outperform Vista from a compatibility perspective, giving Microsoft's customers yet another reason to skip Vista completely and move directly to 7. In fact, when you combine this fact with Windows 7's much speedier performance, lower system requirements, and usability enhancements, it's pretty clear that Vista will be the most quickly abandoned version of Windows since Windows Me.

[ Read about Windows 7 Beta features for businesses. ]

With regards to application compatibility specifically, Microsoft has "rescued" (their word) some applications that were broken in Vista. Many of these applications are international applications: Microsoft says that it is testing over 1,200 applications across 25 markets for Windows 7; 300 are international applications that were not tested against Windows Vista.

The baseline in Windows 7 remains Vista: If it works in Vista, it must work in Windows 7 as well. But even with the application compatibility improvements that occurred in Vista through the release of SP1 last year--and we can't underscore how dramatic those improvements really were--there remains a huge delta when you compare application compatibility on Windows XP with that of Vista. To date, Microsoft has identified 30 applications that run fine on XP but were broken on Vista and now work properly in Windows 7. This number will go up dramatically over the next several months as well, of course.

To US residents, the initial list of newly working apps won't seem particularly compelling--there's a traditional Chinese version of Cyberlink DVD Suite v6, for example, and the German version of QuickTime 7.1.6--but the point isn't so much the identity of the specific applications as it is the revelation that Microsoft is even working on this. Remember, the Windows division is in a mode in which they refuse to over-promise and under-deliver. It's only going to get better.

[ Read about compatibility in the Windows 7 Beta. ]

If you're interested in testing your own applications against Windows 7, Microsoft announced its Windows 7 and Windows Server 2008 R2 Ecosystem Readiness Program earlier this year. This program provides a number of tools, including the Windows Application Compatibility Cookbook, which includes information about testing your wares against Microsoft's next-generation OSs. And the tools are valid now because Microsoft promises that the underlying APIs won't change between January's beta release and the final version, due later this year.

Put simply, the value of XP-to-Windows 7 migrations compared to XP-to-Vista migrations has been something of a toss-up. But I think this announcement--along with presumed future enhancements to Windows 7 application compatibility and the OS's other improvements--will put Windows 7 over the top. Expect to hear more on this front in the days ahead.

An edited version of this article appeared in the March 17, 2009 issue of Windows IT Pro UPDATE. --Paul