Mainframe Job Control Language (JCL): Which function do JCL statements primarily serve in batch processing on IBM-style operating systems—specifically, what do they tell the operating system about the start and end of a job and its steps?

Introduction / Context:
Job Control Language (JCL) is the command language used on IBM mainframe systems (such as MVS, z/OS) to describe batch jobs. Understanding what JCL statements actually do is essential for operations, scheduling, and batch troubleshooting in enterprise computing environments.

Given Data / Assumptions:

• The context is batch processing on IBM-style systems.
• JCL statements accompany programs but are not the programs themselves.
• We are distinguishing between job description (JCL) and resource management (handled by OS subsystems).

Concept / Approach:
JCL does not execute business logic; it instructs the operating system how to run programs: when the job begins, where it ends, which job steps run, what datasets are allocated, and which parameters or procedures apply. While JCL can request resources, it does not itself “allocate the CPU”—the scheduler does that. Nor is JCL merely an input copy tool; it is a control script for batch execution.

Step-by-Step Solution:

Verification / Alternative check:
Basic JCL cards like JOB, EXEC, and DD define job start, program steps, and dataset usage, confirming that the language’s essential function is job specification and control.

Why Other Options Are Wrong:
Reading from card readers or disks is an application/utility function, not JCL’s essence. CPU allocation is an OS scheduling function. “All of the above” overstates JCL’s role.

Common Pitfalls:
Confusing JCL with the programs it invokes; assuming JCL “does” I/O or computation rather than directs them.

Final Answer:
Specify, to the operating system, the beginning and end of a job in a batch