A service program is an i5/OS™ object that contains one or more modules.
You can run programs that are not bound to service programs if they do not require any procedures from the service program. However, you cannot run any procedures from a service program unless that service program is bound to a program. In order to call procedures in a service program, you must export the procedure name. A service program is created using the Create Service Program (CRTSRVPGM) command
While a program has only one entry point, a service program can have multiple entry points. You cannot call service programs directly. You can call procedures in a service program from other procedures in programs and service programs.