Can CICS version 2.1 (Macro Level) run on z/OS?
This is a bit of a 'blast-from-the-past' for me: the 1st significant chunk of CICS Development I did at IBM Hursley was on CICS/ESA 2.1!
Therefore, I am somewhat surprised that this VERY old release of CICS is still in use - it's long been out of service. MVS has evolved into OS/390 and now into z/OS since it was written. The only reason I can think of that CICS/ESA 2.1 is still being used is because there is some ancient code written using the old-style Macro-level programming interface.
My opinion - and it's not anything more than an informed guess - is that z/OS will be incompatable with CICS/ESA 2.1 and so the latter will not run in the former environment. I've come to this conclusion because of the major restructure of the Operating System to work with hardware in in the newer addressing mode may well have introduced coding techniques which the old CICS will not know about.
I'd strongly recommend moving away from this old and unsupported release of CICS - you are running a considerable risk if something goes wrong with an out of service product, especially one as old as CICS/ESA 2.1. In my opinion, any old applications should be rewritten sooner rather than later.
Just as a bit of an aside CICS/ESA 4.1 goes out of service at the end of the year, so you should be thinking to moving to CICS TS 2.2 which requires z/OS >= 1.2
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