At PDC today, Microsoft gave the first public demonstration of Windows 7. Until now, the company has been uncharacteristically secretive about its new OS; over the past few months, Microsoft has let on that the taskbar will undergo a number of changes, and that many bundled applications would be unbundled and shipped with Windows Live instead. There have also been occasional screenshots of some of the new applets like Calculator and Paint. Now that the covers are finally off, the scale of the new OS becomes clear. The user interface has undergone the most radical overhaul and update since the introduction of Windows 95 thirteen years ago.

First, however, it's important to note what Windows 7 isn't. Windows 7 will not contain anything like the kind of far-reaching architectural modifications that Microsoft made with Windows Vista. Vista brought a new display layer and vastly improved security, but that came at a cost: a significant number of (badly-written) applications had difficulty running on Vista. Applications expecting to run with Administrator access were still widespread when Vista was released, and though many software vendors do a great job, there are still those that haven't updated or fixed their software. Similarly, at its launch many hardware vendors did not have drivers that worked with the new sound or video subsystems, leaving many users frustrated.

While windows 7 doesn't undo these architectural changes—they were essential for the long-term health of the platform—it equally hasn't made any more. Any hardware or software that works with Windows Vista should also work correctly with Windows 7, so unlike the transition from XP to Vista, the transition from Vista to 7 won't show any regressions; nothing that used to work will stop working.