During the initial SAP ERP system set up, the basis guy setup the system details like whether it is a CUSTOMER system or SAP system.
Technically if we want to know the system parameters, then the below FM can help us.
Test the Function Module.
Here we can see the system is a CUSTOMER system.
One more example, where the system type as SAP system.
Depending upon the system type, certain configurations can be made and certain are not.
SAPCODES 