On 8/1/2011 9:53 PM, CM Poncelet wrote:
Quite possibly; but it's a contrived case where the 2nd LRECL is a fixed length multiple of the first (so there is one BDW and one RDW, and the records follow each other consecutively in the buffer).
His example used RECFM=FB, so there are no BDWs and no RDWs (if there were, then the first four bytes of the second record would be the RDW, not data).
to avoid I/O errors. Hence, the assertion that DCB attribute override priority is 'program -> JCL -> DASD' is true if the DCB is opened for output; but it is false (or at least 'it does not work', for the benefit of those who can stomach only a politically correct version of the truth) if it is opened for input, because it then hits I/O errors.
DCB is short for Data Control Block. These exist only in memory, and are specific to the zOS operating systems (and earlier MVS and OS/360). I can read DASD written on MVS on VSE, and vice versa. VSE has no DCBs, but it manages to read data anyway.
On DASD, each block of data is preceded by a count field containing a logical (alternate track) or physical address (CCHHR), a key length, and a data length. There is no RECFM, no LRECL, and the physical block may have a length other than that specified by BLKSIZE. Regardless of how often you repeat yourself, there is no DCB on DASD.
Furthermore, your discussion of I/O seems to indicate that either you do not understand English, or that you are unaware of the differences between BSAM and QSAM. I would suggest that you read up on system control blocks, notable the IOB and ICB, look at some in a dump, and get a better understanding of how I/O functions. Requisite manuals are available online. While "Using Data Sets" is a bit daunting, it contains most of the information.
Gerhard Postpischil Bradford, VT ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
