In all the conversations about what is possible on XP and isn't, one thing I've neglected to mention is the idea of WinFX on Longhorn.

Let's take something like Avalon, which will have some limitations on Windows XP. While we are still working out the details, there is a possibility that reliable hardware acceleration may not be possible on Windows XP due to the display driver model. For now, lets imagine that we can't hardware accelerate on XP. Longhorn will still contain the new Longhorn Display Driver Model. This means that WinFX applications running on Longhorn will run with hardware acceleration, even if it isn't possible on Windows XP.

When people worry over limitations that may be imposed on WinFX downlevel, it's important to note that those limitations may be significantly different (or removed altogether) on Longhorn.

Wait! Before you panic about application compatibility. The example above talks about Avalon, today there are already circumstances where software fallback or hardware acceleration will be used - we already ensure that these two modes will be completely compatible.