High Quality Content by WIKIPEDIA articles! The Native API (with capitalized N) is the publicly- and incompletely-documented application programming interface used internally by the Windows NT family of operating systems produced by Microsoft.. It is predominately used during system boot, when other components of Windows are unavailable. The Program Entry point is called DriverEntry(), the same as for a Windows Device Driver. However, the application runs in Ring 3 the same as a regular Windows Application. Most of the Native API calls are implemented in ntoskrnl.exe and are exposed to user mode by ntdll.dll. Some Native API calls are implemented in user mode directly within ntdll.dll.