What happens when you start CICS

When you start CICS®, you start a process called CICS system initialization. This process must finish before you run any transactions.

CICS system initialization involves many activities, some of which are:
  • Obtaining the required storage for CICS execution from the private area in the CICS address space, above and below the 16MB line.
  • Setting up CICS system parameters for the run, as specified by the system initialization parameters.
  • Loading and initializing the CICS domains according to the start option specified by the START system initialization parameter.
  • Loading the CICS nucleus with the required CICS modules.
  • Installing CICS resource definitions by:
    • Loading, from the CSD, the groups of resources specified by the GRPLIST system initialization parameter
    • Loading the control tables specified by system initialization parameters
  • Opening the data sets necessary for initialization, including any needed for backout if the previous run of your CICS region was not shut down normally.
  • Opening BSAM sequential devices as required in the terminal control table (TCT).

If you are operating CICS with CICS recovery options, backout procedures can be used to restore recoverable resources to a logically consistent state. Backout occurs if you start CICS with START=AUTO and CICS detects that the previous shutdown was immediate or uncontrolled.

For background information about backout, and recovery and restart, see Troubleshooting for recovery processing.

Application and system programs are loaded at first reference and are reloaded at first reference after a program compression has occurred.