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significance of 16MB line in COBOL

 
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eeks

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Joined: 06 Jul 2005
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PostPosted: Sat Mar 25, 2006 1:37 pm    Post subject: significance of 16MB line in COBOL
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Hi guys,

Can any one please tell me what is 16MB line ,RMODE and AMODE and where exactly should i use these options?

It would be of immense help if you could provide any links regarding the same.

Thanks in advance,
Arun
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dneufarth

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Joined: 27 Apr 2005
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PostPosted: Sat Mar 25, 2006 6:01 pm    Post subject:
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and your search of the cobol manuals revealed what?
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dneufarth

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PostPosted: Sat Mar 25, 2006 6:48 pm    Post subject:
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sorry, make that search of the forums not cobol manuals
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DavidatK

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PostPosted: Mon Mar 27, 2006 7:41 am    Post subject: Re: significance of 16MB line in COBOL
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Arun,

A long time ago, in the prehistoric days of IMB mainframes, the largest address you could access was 24 bits in length x?FFFFFF? = 16777215 = 16MB. Today, we can access 31 bit addresses, x?7FFFFFFF? = 2147483647 = 2GB.

The AMODE/RMODE are linkage edit parameters that tell the operating system where your program can Run, either below the 16MB line only, or it can run below or above the 16MB line. It also tells the operating system if your program can Access data above the 16 MB. Depending on your parameters, your program will be assembled into an executable module differently.

Why don?t we always specify that the program can Run and Access data above the 16MB line? Most of the reasons are the other programs you are calling. If the program you are calling has not the ability to access data above the 16 MB line, your data must stay below, A lot of legacy programs/subroutines are still compiled/linked to run only below the 16MB line. There are also some performance issues that you may investigate. The operating system (MVS) runs below the 16MB line, and depending on your site configuration, it could leave only 8MB of storage for you to use.

One of the reasons that could force you above the 16MB line is the size of the working storage in your program. If you use very large COBOL tables then the size of the WS + executable code may be more than is available below the 16MB line.

This can cause a perplexing problem. What if the working storage area in your program is to large to fit below the 16MB line, and you must call a subroutine that cannot access data above the 16MB line????????????

I think that most of the time today, the executable code runs below the 16MB line and the Data is above the Line. This seems to be, in my experience, the most common configuration.

Dave
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Ganesh Kalam
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PostPosted: Thu Mar 08, 2007 2:13 am    Post subject:
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What if the working storage area in your program is to large to fit below the 16MB line ?

How to handle this scenario
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William Thompson

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PostPosted: Thu Mar 08, 2007 2:42 am    Post subject:
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Try sticking to a thread, your thread?

If you manage to create a WS too large to fit below the line, you had better have it above the line.... icon_smile.gif
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Ganesh Kalam
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PostPosted: Thu Mar 08, 2007 3:35 am    Post subject: Re: significance of 16MB line in COBOL
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What can be the maximum size of a working storage section ??
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William Thompson

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PostPosted: Thu Mar 08, 2007 3:58 am    Post subject:
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Try sticking to a thread, your thread?
One more time and ! You have been warned.

Look at the Fine Manual
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