You can recompile existing FORTRAN 77 programs from XL Fortran Version 2 with XL Fortran Version 6.1.
The only language features that are not supported are the STRUCTURE, UNION, and MAP constructs from XL Fortran Version 2.3 that required optimizing preprocessor support.
You can link existing FORTRAN 77 object code from XL Fortran Version 1 or 2 into programs generated by XL Fortran Version 6.1. See Linking New Objects with Existing Ones for details.