DWM and WDDM 1.1
When Windows Vista shipped, it included a new driver
model, called the Windows Display Driver Model. That was version 1.0. It's required for the Desktop Window Manager (DWM) to render the desktop using DirectX 9, giving you the neat Aero Glass user interface and Flip3D and such. WDDM is being upgraded to WDDM 1.1, which will be required for some of the new DWM features in Windows 7.
Windows 7 will still run with WDDM 1.0 drivers
, and XP drivers for that matter, but with WDDM 1.0 drivers you won't get any of the DWM improvements, and with XP drivers you don't get Aero Glass or any of its features at all (just as it is with Vista).
So what do you get with WDDM 1.1? For starters, the DWM will use DirectX 10 instead of 9 and offer some nice performance enhancements. DWM will now use the same consistent amount of system memory no matter how many windows are open. Your graphics card memory usage will still increase as you open more windows, but that amount of memory is cut in half relative to Vista.
The end result is that Windows 7 will use dramatically less memory as you open additional windows on your desktop. It should also be faster and more efficient at rendering the desktop.
Windows 7 will introduce Direct2D, a sort of accelerated 2D replacement for GDI used for drawing 2D graphics, lines, splines, etc. It runs on top of Direct3D 10 and requires WDDM 1.1 drivers. This has been long awaited, and future applications should see snappier windows performance in standard applications, not just 3D apps.
DirectX 10 games should see a performance improvement with WDDM 1.1 drivers, mostly centered around memory management. It's still far too early for Microsoft to share any sort of numbers, but it seems to suggest that the performance difference will vary by title. Microsoft Microsoft Windows 7 Next-Gen Graphics7 Cutting Edge Graphics - DWM and WDDM 1.1 - OS, Software & Networking by ExtremeTech