Learn which subsystem is the final one to shut down when a mainframe goes through an Initial Program Load (IPL). Discover why JES2 is always the last to stop during this process.
Table of Contents
Question
Which is the last subsystem to shutdown during IPL?
A. DB2
B. CICS
C. JES2
D. XCOM
Answer
C. JES2
Explanation
JES2, or Job Entry Subsystem 2, is the last subsystem to shut down during an Initial Program Load (IPL) on an IBM mainframe system.
The reason JES2 is last to shut down is because it plays a critical role in managing batch jobs, output processing, and other essential system functions. All other major subsystems like DB2, CICS, and XCOM rely on JES2 to some degree. By keeping JES2 running until the end of the IPL shutdown process, it ensures an orderly shutdown of dependent subsystems first.
During an IPL, JES2 orchestrates the systematic shutdown of subsystems in the proper order based on their interdependencies. For example, DB2 databases and CICS regions will be brought down before JES2 since they rely on JES2 services. XCOM, which handles remote data transfers, also depends on JES2 indirectly.
Only after all other major subsystems have successfully shut down will JES2 itself terminate. This sequential flow is critical for avoiding disruptions and allowing the mainframe to restart cleanly during the next IPL.
So in summary, JES2 is always the final subsystem to go offline during any mainframe IPL procedure due to its central role in the overall system. Keeping JES2 up until the end allows for the graceful closure of all other subsystems that depend on it directly or indirectly.
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