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sanat · Posted: Sat Feb 15, 2003 7:34 am Post subject: multi user facility

How CICS allow hundreds of thousands users concurrently ? How CICS allow multiple transactions to run concurrently without any major problems
where as in a Clien/Server environment no. of user access has got many limitaions ?
Link to manuals is also welcome.

kolusu · Posted: Sat Feb 15, 2003 9:36 am Post subject:

sanat,

CICS is a multitasking, multithreading system environment. Multitasking means that CICS provides an environment where more than one CICS task runs concurrently. Multithreading means that tasks share the same program in a multitasking environment. CICS is characterized as multitasking and multithreading because it provides an environment in which multiple CICS tasks, using the same program, can run concurrently.

IBM introduced CICS in 1969. CICS controls concurrent execution of application programs in a multiprogramming environment within the CICS region or partition. CICS overlaps I/O (Input/Output) operations and processing between multiple tasks. When several tasks require use of the same program, only one copy is maintained in storage by CICS utilizing a process called multithreading. CICS uses a "task control area" for each task to manage this processing. Programs cannot modify themselves because they can be used by more than one task at a time - they must be reentrant (or quasi-reentrant). For COBOL, CICS makes a copy of working-storage for each task so that the program may be used in this multithreading environment.

As for the manuals, you can access all IBM and other mainframe related manuals from the main page of mvsforum

www.mvsforums.com

for CICS

http://publibz.boulder.ibm.com/cgi-bin/bookmgr_OS390/FINDBOOK?filter=cics

Hope this helps...

cheers

kolusu

sanat · Posted: Mon Feb 17, 2003 9:45 am Post subject:

Kolusu,
In fact it was an interview question. I was asked in comparison to Client -Server environment how the CICS handles millions of concurrent users and successfully handles hundreds thosand transactions at the same time.
When we talk of multi-tasking we have the same in C/S system. And the multi threading concept comes to picture when more than users run the same transaction/module. Even the virtual memory concept is very much there in C/S system.
I just want to know what is the speciality about CICS. I have gone thru some of the books but only programming features are described there.

Regards,
Sanat.