Re: CICS/400

Ahh MRTs! And THEN when you decided you needed to save a few more pointers or variables per user in the MRT data Structure, or you discovered you needed to support 20 users instead of 10, and the compile failed. Why? 64KB Program maximum size. Yeah, that's a 'K'. :-)

- DrF

On 8/12/2023 1:57 PM, Jon Paris wrote:

I don't think I can do much better than Mark's great explanation Jack.

The only thing I might mention is that the S/38 - IBM i paradigm of interactive programming relies on an underlying OS feature - namely that there is only ever one copy of the program instructions in memory and the system always automagically handles _all_ of the memory for a user and associates it with the program when needed. So state information (including current file cursor positions etc.) is retained with _zero_ effort on the part of the programmer.

S/34/36 MRT programmers had to actually decide which variables (including of course current file positions) needed to be retained between messages and on receipt of a new message they had to "page in" the appropriate set of variables, reposition file cursors, etc. CICS is much the same except that there is some built-in functionality to assist in the storage etc. of state information. In both cases this programming had to be done without the assistance of pinter-based dynamic memory - so making decisions about which variables were to be retained was a major effort.


Jon P

On Aug 11, 2023, at 2:21 PM, Jack Woehr via MIDRANGE-L <midrange-l@xxxxxxxxxxxxxxxxxx> wrote:

It might be interesting if you would expand on those remarks.

On Fri, Aug 11, 2023 at 12:19 PM Jon Paris <jon.paris@xxxxxxxxxxxxxx> wrote:

For anyone who has ever done S/36 MRT programming CICS is pretty simple.

For those who grew up on the S/38 / AS/400 with the "why should I have to
worry about state information?) mentality it is much harder. In some ways
it is the same reason that programmers with that background have difficulty
getting their heads around web programming. S/36 MRT programmers find the
web a breeze!

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