As one example, every Windows program, even the newest Win32 program, requires a DOS data structure, called the Program Segment Prefix (PSP), which the system allocates in conventional memory, and initializes with a DOS call (INT 21h function 55h). And every program that exits, whether DOS, Win16, or Win32, calls the DOS Terminate Process function (INT 21h function 4Ch). Win95 most certainly does sit on top of DOS, albeit a copy of DOS that comes in the same package.