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where the execution takes place?

 
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rajarajeswari

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Joined: 25 Aug 2006
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PostPosted: Thu Sep 11, 2008 2:59 pm    Post subject: where the execution takes place?
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Hi

Please clear me on this question.

Which will execute the job?

1. OS
2. JCL
3. JES
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expat

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PostPosted: Thu Sep 11, 2008 3:01 pm    Post subject:
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The JCL (job) is interpreted via JES2 and passed to the operating system for execution.
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rajarajeswari

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PostPosted: Sun Sep 21, 2008 8:44 am    Post subject: where the execution takes place?
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Thanks for your reply
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nevilh

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PostPosted: Mon Sep 22, 2008 8:19 pm    Post subject:
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expat wrote:
The JCL (job) is interpreted via JES2 and passed to the operating system for execution.
Are you sure about this? I always thought that interpretation was done by z/OS and conversion was done by JES (simplistic view)
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superk

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PostPosted: Mon Sep 22, 2008 8:50 pm    Post subject: Reply to: where the execution takes place?
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I'll copy a few items from the z/OS Basics manual Chapter 7.1 What is Batch Processing:

Quote:

z/OS uses a Job Entry System or JES to receive jobs into the operating system, to schedule them for processing by z/OS, and to control their output processing.

z/OS manages work as tasks and subtasks. JES is a component of z/OS and manages the the input and output job queues and data.

The initiator is an integral part of z/OS that reads, interprets, and executes the JCL.

Job Flow

JES accepts jobs, in the form of an input stream, from the internal reader. JES reads the input stream, assigns a job identifier to each JOB statement, and places the information onto a spool dataset. JES then selects jobs from the spool for processing.

JES uses a converter program to analyze a job's JCL statements. The converter converts the composite JCL converter/interpreter into text that both JES and the initiator can recognize. JES then stores the converted text onto the spool datasets.

In the processing phase, JES selects jobs that are waiting to run and sends them to the initiator for execution. An initiator is a system program belonging to z/OS but controlled by JES or Workload Management (WLM).
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nevilh

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PostPosted: Tue Sep 23, 2008 12:59 am    Post subject:
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Quote:
Are you sure about this?
I added this as I was always lead to believe that after the Converter/interpreter code was redesigned in the early 90's that conversion was the reponsibility of JES and interpretation was in the domain of z/OS. I never questioned this, it was just the way things were. Having read the reply I had a quick look in the manuals and found contradictory statements. Hence the question, as until I read the reply I had no doubts and now I am not so sure. The exits manual clearly states that
Quote:
MVS creates the C/I text and uses it in its preparation for executing your job. IBM recommends that you do not modify this text.
Added to this all Interpreter modules belong to z/OS. However now the down side (from my point of view) the Converter modules also belong to z/OS and I am 99% sure this is a function of JES so can anyone put me out of my misery and point me to a manual that will answer the question
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