This is not something I lose sleep over, only something I'm interested in. Take a look at the second rig in my sig. Fairly ancient, this is the point.
Now let's put Window Vista or 7 on it (performs the same). Then let's benchmark 2 scenarios:
#1: WDM XP drivers installed
#2 WDDM Vista drivers installed
#1 has decent 3D performance, actually faster than XP drivers on XP. (However, it's pretty ugly without aero...)
#2 has approx 25-30% less performance. The performance loss seems to be CPU related, as any graphics settings will provide smaller frame rates. The higher the graphics settings, the closer the results of the two benchmarks go to each other.
Note #1: It's not the aero effect or dwm, I disabled both for the banchmark. Even using the WDDM driver windows renders stuff in fallback mode.
Note #2: It cannot be the WDDM driver being unoptimized. It's an X1xx series card, whose driver went throgh a 3-year developement cycle. AMD optimizes drivers to max performance in approx 0,5-1 years.
So... Is it WDDM being that *****on single core CPUs? Is it a bloatware we don't notice on modern computers? Any ideas?
CPU: AMD Phenom II X4 810 @ 3120MHz | RAM: Kingmax 2x2GB DDR2 800 @ 833MHz| MoBo: MSI K9A2 CF v1.0 (BIOS: 1.D)| GPU: Asus HD 6850 1024MB (DirectCu) @ 835/1135MHz | Display: L24FHD | PSU: PC Power & Cooling Silencer 750 Quad | OS: MS Windows 3.11 Pro x64