Enterprise PL/I V4R1 contains some new options and some old options with new suboptions. However, the defaults for these new options and suboptions produce executable code that is compatible with the code that is produced by the Enterprise PL/I V3R9 compiler (or any of the releases since V3R3).
If you use with PL/I Version 4 the same settings for your compiler options as you used with the Version 3 releases, you can mix code compiled with V4R1 and earlier releases. You do not need to recompile all your code unless you change the setting of a compiler option that changes the program semantics. For example, you can freely change the ARCH or RULES option when mixing objects, but you cannot do so if you change the BACKREG, BIFPREC, or CMPAT options.
The new options and changed options are listed as follows. They are described fully in the Programming Guide.