Why CICS is Used

Companies do not use CICS because it is fashionable. They use it because their business stops if thousands of customers cannot get instant answers from the mainframe at the same time.

The business problem CICS solves

• Hundreds or thousands of users need the same data at the same time - bank balances, seat availability, stock levels.
• Each user expects an answer in one or two seconds, not tomorrow morning.
• The data must stay correct even when two users update the same record at the same moment.
• Batch processing cannot do any of this. It runs without users and delivers results later.

Main reasons companies choose CICS

• Speed - sub-second to few-second response time for online users.
• Concurrency - thousands of simultaneous users sharing the same programs and data.
• Data integrity - commit and rollback (SYNCPOINT) keep data correct even when programs fail midway.
• Security - sign-on control plus resource-level protection for transactions, files and programs.
• Availability - designed to run 24x7 with facilities for restart and recovery.
• Scalability - workload can be spread across multiple CICS regions (MRO) as demand grows.
• Investment protection - COBOL applications written decades ago still run on the latest CICS.

Real-life examples

• ATM withdrawal - the ATM is the terminal, CICS runs the transaction, and your balance updates instantly.
• Flight booking - two agents cannot sell the same seat because CICS serializes the update.
• Insurance claim enquiry - the agent sees policy details on screen within seconds.
• Online shopping order - the order is taken online and the stock file is updated at once.

Starting a CICS region

• A CICS region is started as a z/OS started task with JCL like the one below. DFHSIP is the CICS system initialization program:-
  //CICSREGN JOB (ACCT),'START CICS',CLASS=A,MSGCLASS=X //STARTCICS EXEC PGM=DFHSIP,REGION=0M,TIME=1440, // PARM='START=AUTO,SYSIN' //STEPLIB DD DSN=CICS.SDFHLOAD,DISP=SHR //DFHRPL DD DSN=CICS.SDFHLOAD,DISP=SHR // DD DSN=USER.CICS.LOADLIB,DISP=SHR
• Note:- STEPLIB points to the CICS program library (SDFHLOAD) and DFHRPL points to libraries containing your application programs.