HOW to check where a system is ABAP stack or dual stack(ABAP + java).

method- 1

 sm51

  under message types, J2EE stands for dual stack

If not

ABAP stack.

Method-2
smicm-->menu bar-->GO TO --> services --> is J2EE server is there then, the system is dual stack
                     

                                                                      else

                                                                      ABAP stack
Method - 3

 if Operating system level access is there then, this method will be applicable, where as for the above 2 methods GUI access is enough.

access

usr/sap/sid/instance/J2EE


is J2EE file is present then, system is dual stack otherwise ABAP stack only.