Every Control Panel application is a dynamic-link library. To make sure the DLL containing your Control Panel application can be located and automatically loaded by the Windows system utility, the DLL file must have the .CPL filename extension and must be set up in one of the following ways:
·Copied to the directory that contains the Windows system utility.
·Copied to the Windows SYSTEM directory.
·Registered under the the MMCPL key of the HKEY_CURRENT_USER key in the registry.
You should register the DLL in the registry if the DLL exports functions other than CPlApplet and provides functionality beyond the scope of a Control Panel application. For more information about the registry, see Registry.