RE: How does this software work??

Steve,

You say:
>>>>
Before there were all the system api's, I can see the tool code
breaking,
but what v5r1 tool would be release dependent and why?
<<<<

You can use strictly API"s and code can still break with a new release.
As has already been pointed out elsewhere, there is the Library List
issue on V5R1.

Then there is the enlarged spool file number of V5R1.

V3R2 (or thereabouts) changed the size of internal spool headers so
some of the low level spool api's stopped working.

V3R1 broke lots of code.  Wait...I'm wrong here.  It was V3R1 that was
broken.  Not our code.  But we still had to make changes to anything
using APPC under early versions of V3R1.

And to pick on V5R1 a bit more, I am having an issue where all of a
sudden a call to QMHSNDPM is not working (On the C400 list, Philip Hall
might have found the problem for me).  This particular issue might be a
coding error, but this "error" has worked since V2R3.

So yes, it is very possible to follow all the rules and still have code
break with new releases.  Of course, code that breaks the rules is much
more likely to break than code that doesn't.  And I would also
postulate that MI is much more likely to break than anything else.

You should always check with your vendors before upgrading.

And yes,  I would agree that Fast400 is likely to be intentionally
broken by IBM.  They might warn you.  But they might not.

Regards,
Bob Crothers
Cornerstone Communications
http://www.cstoneindy.com