What are the parameters defined for a load module dataset?

[DannyG]

hi,

What are the parameters usually defined for a load module dataset? I have not noticed it and did not answer this in the interview. Later I found that we use the following parameters:

Code: Select all

Organization  . . . : PO        
 Record format . . . : U        
 Record length . . . : 0        
 Block size  . . . . : 32760  

Are these the only parameters we use for a load module or there can be other combinations? Thanks for any help.

[Robert Sample]

A load library is partitioned (either PDS or PDSE), with record format U, no record length, and some block size. The block size should be large for efficiency but older utility programs sometimes create load modules with smaller block sizes. The IEBCOPY COPYMOD utility control statement allows load modules to be copied and reblocked when the block size of the input and output data sets are different.

[DannyG]

Thanks. So I was also correct? Or you mean to say that 32760 is not always the case?

[nicc]

The block size should be large for efficiency but older utility programs sometimes create load modules with smaller block sizes.

What is unclear about that? Note the words 'should', 'large', 'but' and 'smaller'.

[enrico-sorichetti]

32760 is the right value for a PDSE ( library ) load module dataset

for NON PDSE datasets 27998 ( 3390 geometry ) will be more appropriate

[Gerhard_Adam]

The blocksize is largely irrelevant. You will find it ranging from 6144 to 13030 to 19069 to 32760. It has little to do with anything in a load library. It doesn't really do anything for efficiency, because only the TXT records in a load module are subject to blocking. Since these records are only read during program load, it has virtually no effect on performance.

The average size of a record in a load library is less than 256 bytes, which is why the RECFM=U. This is undefined because there is no concept of a logical record and therefore the LRECL=0.

While the attributes will be the same for a PDS and a PDSE, do not confuse these two as being interchangeable. They are not.

A PDS contains a load module, while a PDSE contains a program object. They are both created by the Linkage Editor/Binder, but they are not the same thing. Do not attempt to use a PDSE [for program objects] unless it is specifically supported and the same applies in reverse.

[DannyG]

 It doesn't really do anything for efficiency, because only the TXT records in a load module are subject to blocking.  Since these records are only read during program load, it has virtually no effect on performance.

What is a TXT record and what is their purpose for a load module?

The average size of a record in a load library is less than 256 bytes, which is why the RECFM=U.  This is undefined because there is no concept of a logical record and therefore the LRECL=0.

Sorry I did not understand it. If "the average size of a record in a load library is less than 256 bytes" why it needs to be undefined, it could be VB?
And again

A PDS contains a load module, while a PDSE contains a program object.

 But Robert said:

A load library is partitioned (either PDS or PDSE), with record format U, no record length, and some block size.

So what PDS can have load or object?

[Robert Sample]

[justify]A PDS can only store a load module while a PDSE stores program objects.  They are both typically called load libraries.  The differences are that a load module limits external references to 8 characters while program objects can have external references up to 32767 bytes long and a load module can only have 32767 external references while program objects external references are only limited by memory available.  Program objects are the "new" (as of 1995) way of creating executable code on a system z machine, but IBM continues to support load modules for backwards compatibility.  Program objects can also be stored in a Unix directory.  There are a few data sets that must still be a PDS (since the PDSE code is not loaded when the system IPL starts), but generally all other load modules can be converted to program objects.[/justify]