Vista moved graphics mostly out of kernel even if part of GDI was still handled internally, but essentially the driver model changed heavily and enabled restartable drivers and by Windows 7 IIRC the new model was mandatory.
In "classic" Windows and NT 4.0 - 5.2 GDI would draw directly into VRAM, possibly calling driver-specific acceleration routines. This is how infamous "ghosting" issues when parts of the system would hang happened.
With new model in Vista and later, GDI was directed at separate surface that was later used as texture and composited on screen. Some fast paths were still available to bypass that mainly for full screen apps, and were improved over time.
In "classic" Windows and NT 4.0 - 5.2 GDI would draw directly into VRAM, possibly calling driver-specific acceleration routines. This is how infamous "ghosting" issues when parts of the system would hang happened.
With new model in Vista and later, GDI was directed at separate surface that was later used as texture and composited on screen. Some fast paths were still available to bypass that mainly for full screen apps, and were improved over time.