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to_agrawals · Beginner Joined: 12 Dec 2002 Posts: 26 Topics: 16

Hi,
I tried to search but I didnot get a concvincing answer to tell the precise differnce between the two. When should we use which is not clear. What I know is that blocked implies that the i/o happens in blocks. But when i tried to allocate a dataset with RECFM=FB and not specifying the BLKSIZE, it still allocates the dataset.
Can anyone comment.
Thanks

kolusu · Posted: Wed May 07, 2003 6:11 am Post subject:

Agarwal,

The biggest difference between RECFM=F and RECFM=FB is the blocking.

FB stands for FIXED BLOCK which means the records are blocked (logical records grouped into larger physical records) whereas the RECFM=F is not blocked and the logical record is the same as the block.

check this link and at the bottom of the link you will have a graphically image explaining the blocked records vs unblocked records.

http://publibz.boulder.ibm.com/cgi-bin/bookmgr_OS390/BOOKS/IGYA1101/4.2.2.1?DT=19930312141355

RECFM=FB is considered to be more efficient.Most shops have standard routines which will calculate the optimum blocksize when allocating.Check this link for calculating the space attibutes for a dataset. It has explanation about the blocksizes.

http://www.mvsforums.com/helpboards/viewtopic.php?t=28

Hope this helps...

cheers

kolusu

piper · Beginner Joined: 07 May 2003 Posts: 2 Topics: 0

So What's the difference between FB and FBA?

Frank Yaeger · Posted: Wed May 07, 2003 11:31 am Post subject:

FBA is FB with an ANSI (printer) carriage control character in the first byte of each record, e.g. '1' for page eject, ' ' for single space, '0' for double space, '-' for triple space, etc. For FB, the data starts in position 1. For FBA, the data starts in position 2 after the ANSI character.
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