The BLKSIZE of SYSLIN is optional for the Assembler and COBOL compilers. In other words, if the SYSLIN data set is allocated with BLKSIZE=0, then ASMH, HLASM and COBOL2 force BLKSIZE=80, and today's COBOL3 (Enterprise COBOL) forces BLKSIZE=3200. Why 3200? Probably because the old Linkage-Editor (now called HEWLKED) fails when the value of BLKSIZE of SYSLIN is above 3200. The Binder (IEWL) has no maximum BLKSIZE, so you can't code anything above BLKSIZE=3200 if you use the old linkage-editor (HEWLKED) but can code up to BLKSIZE=32720 if you use the Binder (IEWL).
IIRC, it was in DFP 2.3 (1988?) that OPEN was changed and started to calculate an optimal half-track BLKSIZE when BLKSIZE=0. In spite of that, twenty years later, HLASM still forces BLKSIZE=80 instead of letting OPEN calculate a half-track BLKSIZE. Why? I don't know. Similarly, today's Enterprise COBOL still forces BLKSIZE=3200 instead of letting OPEN calculate a half-track BLKSIZE. Why? I don't know either. OK, perhaps I know why, but I think it would be better if HLASM and COBOL let OPEN calculate the BLKSIZE. Some utility programs rely on another issue about the BLKSIZE of concatenated data sets. In the old days, the BLKSIZE of the first data set did override the BLKSIZE of the data sets concatenated to it. This was true for sequential or partitioned data sets, so you had to make sure the largest BLKSIZE was first, or that you forced it in the first DD stmt. Today, of course, this is no longer true. In fact, when concatenated sequential data sets are processed since DFP 2.3, EOV updates the BLKSIZE each time it starts reading a new sequential data set. When partitioned data sets are concatenated, then OPEN inspects all of the F1-DSCBs and uses the largest BLKSIZE it finds to allocate a buffer pool. So, does the largest BLKSIZE need to be specified in the JCL for concatenated data sets today? Well, generally it doesn't. Unless, as I said, in steps which execute a program which behaves poorly. -- Gilbert Saint-Flour GSF Software http://gsf-soft.com/ ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
