The Windows NT graphics architecture has significantly changed in Release 4.0. The biggest change is the move of GDI and graphics drivers into the Windows NT executive. For this reason, all pre-4.0 graphics drivers must be ported and rebuilt to run on NT4.0. Several new support routines have been added to kernel-mode GDI, including routines for kernel-mode memory management, synchronization, and file mapping.
See Porting Graphics Drivers To Windows NT 4.0 from 3.51 for details.