The display driver controls all writing to the built-in display hardware of the system. Typically, this is an LCD screen, but it can be any sort of display hardware that is suitable to your target platform. In Windows CE 2.0 and later, the display driver model for built-in display hardware is the same as the model for peripheral display adapter drivers.
By default, Windows CE uses built-in display hardware that cannot be removed by a user. Windows CE can also use removable peripheral display adapters, usually in the form of PC Cards. For either type, your display driver DLL must be named Ddi.dll.
Create a registry key under HKEY_LOCAL_MACHINE\Drivers\Display to store configuration entries for your display driver. In addition, the initialization routine of your display driver should create keys under HKEY_LOCAL_MACHINE\Drivers\Display\Active so that applications can determine which display devices are available.