Historic information about the "DCB parameter in the DD

Ricardo Viegas · New User Joined: 18 Oct 2012 Posts: 39 Location: Brasil

Hello!
Does, by any chance, anybody knows when it started to be possible to code the sub-parameters of the DCB parameter directly, as parameters, in the DD card?

I was able to trace back that this was already possible in the OS/390-V2R6, according to a JCL Reference manual dated September/1998
In that manual, and in all its following versions, there is the following statement:

"Alternate syntax for DCB keyword subparameters: All of the DCB keyword subparameters can be specified without the need to code DCB=. For example, the following DD statement:
//DDEX DD DSNAME=WKDATA,DCB=(RECFM=FB,LRECL=80,BLKSIZE=800),DISP=MOD
can also be specified as:
//DDEX DD DSNAME=WKDATA,RECFM=FB,LRECL=80,BLKSIZE=800,DISP=MOD"

I am in a need to now when this kind of "simplification" of coding started. That need emerged during the teaching of an introductory (but extensive - 7 weeks) course about z/OS characteristics, functions, sub-systems, etc directed to prepare "very junior" systems programmers.

Any indication/hint about that will be really appreciated.
Thanks in advance!
Regards, Ricardo

Nic Clouston · Posted: Fri Nov 01, 2013 2:54 pm

I think I was doing it in the late 80s.

Pete Wilson · Posted: Mon Nov 04, 2013 8:58 pm

It was when DFP v3.1 (MVS 4.3) was introduced, around 1989-1990 (ish). I found a document I wrote on the subject dated for our user community in Oct 1990. At the same time there were new JCL keyords introduced to allow VSAM to be allocated via JCL where in the past it could only be done via IDCAMS or TSO. The LIKE= and REFDD= keywords also emerged, and System Determined Blksize (SDB) amongst other things.

don.leahy · Posted: Tue Nov 05, 2013 12:17 am

It's funny, but even after all this time I still catch myself coding:

DCB=(RECFM=FB,LRECL=80)

But I never code a BLKSIZE by accident anymore; I always rely on SDB unless there is a special reason not to.

Ed Goodman · Active Member Joined: 08 Jun 2011 Posts: 556 Location: USA

no kidding, we still have people here that will fail a tech review if the format is not dcb=(xxxxx).

They learned JCL 30 years ago and by gum it's going to stay that way.

No IF statements, no BLKSIZE=0, and you have to specify a volume serial even though we've had SMS installed for more than a decade.

steve-myers · Posted: Mon Dec 09, 2013 5:19 pm

Mr. Goodman and others are right. Heck, I learned JCL in the 1960s, when it was DSNAME=xxx and VOLUME=SER=xxx. and I still use DCB=(RECFM=... even though I know I can use just RECFM=.... I almost always use system determined BLKSIZE, which is some sort of new fangled thing that came about when I no longer had to use DCB=(...).

Even though I'm a dinosaur that keeps to the old ways I am not so foolish as to insist you young 'uns use them, and I do adopt new ways when it makes sense, like system determined BLKSIZE. I remember coding complex DCB open exits that did something like system determined BLKSIZE before it became standard. Believe me, I do not want to return to those days!