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JCL Limits

 
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vikram gopalarathinam

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Joined: 28 Jan 2012
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PostPosted: Wed May 09, 2012 5:03 pm    Post subject: JCL Limits
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icon_smile.gif Hi we all know only 255 steps can be allowed in a JCL and 15 instream procs are allowed in a job and 3273 DD statments are allowed.. icon_eek.gif May i know why are this limits and on which condition these limits are set. I want o know in details.. please give me some idea or tell me some good url to know abt this... icon_exclaim.gif
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PeterHolland

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PostPosted: Wed May 09, 2012 5:22 pm    Post subject:
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http://www-01.ibm.com/support/docview.wss?uid=isg3T1000065
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David Robinson

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PostPosted: Wed May 09, 2012 5:28 pm    Post subject:
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255 crops up in all sorts of places as it's the highest number you can store in one byte - x'FF'
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Craq Giegerich

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Joined: 19 May 2007
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Location: Virginia, USA

PostPosted: Wed May 09, 2012 5:36 pm    Post subject: Re: JCL Limits
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vikram gopalarathinam wrote:
icon_smile.gif Hi we all know only 255 steps can be allowed in a JCL and 15 instream procs are allowed in a job and 3273 DD statments are allowed.. icon_eek.gif May i know why are this limits and on which condition these limits are set. I want o know in details.. please give me some idea or tell me some good url to know abt this... icon_exclaim.gif


The limitations are in place because computers are finite machines with finite resources. If you are having problems with them I think you have serious design (or implementation) problems.
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vikram gopalarathinam

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PostPosted: Wed May 09, 2012 5:45 pm    Post subject: Reply to: JCL Limits
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thanks David icon_neutral.gif I agree with your point why is the the limits for DD statments and 15 instream procs..I need to know a detailed info abt this. please give me some URL or any document to know abt that if u have..
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Robert Sample

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PostPosted: Wed May 09, 2012 5:51 pm    Post subject:
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In some cases, the limits come about due to physical restrictions (255, 15 are numbers that are upper limits of 2-byte and 1-byte counters respectively). Others come about indirectly (3273 DD statements in a job, for example, is a limit because that's how many 20-byte DD statements can be defined in a 64 KB TIOT).

MUCH more important than knowing WHY the limit, however, is knowing the actual value for the limit to ensure you don't design anything that would violate a limit. Many of the specific values go back to design decisions made in the early to mid 1960's when the original S360 was being designed and built, and have not been changed to ensure backward compatibility. It is unlikely at this date that you could EVER find out the precise WHY of these design decisions, but remember the machines were much smaller in those days -- memory sizes were 16, 32, 64 KB (etc) for the entire mainframe.
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Phrzby Phil

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PostPosted: Wed May 09, 2012 5:55 pm    Post subject:
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While these are certainly interesting questions and the answers inform us about how these things are implemented, why you need to know this remains a mystery. Why do you need?
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dick scherrer

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PostPosted: Wed May 09, 2012 9:47 pm    Post subject:
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Hello,

Quote:
I need to know a detailed info abt this.
What kind of detail are you looking for?

As Phil asked - why does someone believe there is a need for "detail"?

If we knew what you are trying to address, we might be able to offer more usefull replies.
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vikram gopalarathinam

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PostPosted: Thu May 10, 2012 12:26 pm    Post subject: Reply to: JCL Limits
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Hi..

I have been asked these questions in an interview. Just want to know what willbe the answers for this and certainly it is intresting to know icon_exclaim.gif
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Bill Woodger

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Joined: 09 Mar 2011
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PostPosted: Thu May 10, 2012 1:11 pm    Post subject: Reply to: JCL Limits
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The chance that you'll ever need to know these answers "in detail" and from memory is very, very, slim.

I've never been bothered by them. If I thought I might be in some circumstance, then what is important is knowing how to find out.

A dumb interview question, that could only check fro whether someone has researched answers to dumb interview questions.

OK, they happen. Don't answer them directly, they do not deserve a direct answer in an interview. Answer them "well" instead. For instance, toss a few manual (names) at them, and as an aside say that you've never, ever, heard of anyone having a problem with them...
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