Storage protection

CICS allows you to run your application programs in either user-key or CICS-key storage. CICS storage is automatically protected from being overwritten by application programs that execute in user-key storage (the default).

The concept of isolating CICS code and control blocks (CICS internal data areas) from user application programs is illustrated in Figure 1.
Figure 1. Protecting CICS code and control blocks from user application programs
Diagram showing CICS (executing in CICS-key) with READ/WRITE access to CICS-key and user-key storage and all CICS and user code and data areas. The user application has only READ access to CICS-key storage, code and control blocks, and has READ/WRITE access to user-key storage and user application programs and data areas.