CICS Features

CICS is popular because it packs many features into one system - multitasking, data protection, security and recovery - so programmers can focus on business logic instead of system plumbing.

Multitasking and multi-user support

• CICS runs many tasks at the same time. This is called multitasking.
• Many users can run the same program at the same time from one copy in memory. This is called multi-user support.
• CICS uses quasi-reentrancy - it switches between tasks only at safe points (EXEC CICS commands), so one copy of the program is never corrupted by two users.
• Each user gets fast response because CICS gives the processor to the task that is ready to run.

Resource management

• CICS centrally manages files, programs, maps, temporary storage queues and transient data queues.
• Programs ask CICS for resources with EXEC CICS commands instead of opening files themselves.
• CICS controls who can use which resource and serializes updates so two tasks cannot corrupt the same record.
• Resources are defined once (with CEDA/RDO) and shared by all programs.

Data integrity and recovery

• CICS supports commit and rollback through the SYNCPOINT command.
• EXEC CICS SYNCPOINT makes all changes since the last syncpoint permanent.
• If the program fails before syncpoint, CICS backs out the changes so data stays consistent.
• CICS keeps journals and logs, so work can be recovered and restarted after a system failure.
• Example - committing the work done so far:-
  EXEC CICS SYNCPOINT END-EXEC.

Security, availability and more

• Security - users sign on (CESN) and CICS checks their authority for each transaction, file and program.
• High availability - CICS is built to run continuously, with emergency and warm restart facilities.
• Conversational support - CICS supports both conversational and pseudo-conversational programming styles.
• Connectivity - modern CICS connects to web services, MQ, DB2 and distributed systems.