Comment by p_l

Vista was dogged by issues caused by migrating display drivers from NTDDM to WDDM 1.0, something that was only finished by 7 (which dropped NTDDM fully and introduced WDDM 1.1) and 8 (which afaik had mandated WDDM 1.1 only).

Unlike previous GDI acceleration, DWM.EXE could composite alpha channel quickly with the GPU, and generally achieved much higher fill rates on the same hw - if the drivers worked properly.