If your program reads or writes files, you must use the FTN command to run the program and specify the files. Before you can use any subroutines in your overlays, you must bring the overlays into memory. Each call takes one argument which is the name of the overlay to bring into memory. The name is exactly the same name that you used as your first argument to the RUNL LINK statement for that overlay. This subroutine brings the named overlay into memory and transfers control to either the beginning of the overlay or else to the entry point you specified as the third name in your RUNL LINK directive.
Control returns immediately to the statement following the call, as usual.
This is used for overlays full of subroutines. Once the link is in memory, you may call the subroutines in it normally. One main program with three overlays, all loaded at the same place in memory. Note that each subroutine must be compiled into its own separate object file, since each subroutine is a separate overlay. The main program must also be compiled separately.