In a message dated 5/4/2007 9:11:40 A.M. Central Daylight Time, [EMAIL PROTECTED] writes: >The second is concerning the minimal physical unit a program can process on zos. I know acess method macros like QSAM are still at the high level. From what you told me, I guess the minimal unit QSAM can process is one physical block. The "minimum physical unit a program can process on zos", depending on the "program", is a DASD block containing zero bytes. This kind of block is also called an EOF [1] record. One byte is even easier. But the "program" cannot use QSAM to process the physical unit. And this hypothetical DASD block with zero bytes in its data field has nothing to do with BLKSIZE=ZERO. Obviously, you have to be doing your own channel programming to read or write a block with zero bytes in it, which means you use EXCP, EXCPVR, XDAP, or STARTIO. If you want to, e.g., you can write a full track of zero-byte blocks on DASD. And you can even see them if you dump the track with something like IMASPZAP. How useful a trackful of zero-byte blocks might be is another question, but you didn't ask about that. Bill Fairchild Plainfield, IL
[1] End of File, since reading such a block back in causes higher level access methods to treat such a block as one written to mark the end of a series of blocks with greater than zero data field lengths. "If there is one principle more deeply rooted in the mind of every American, it is that we should have nothing to do with conquest." [Thomas Jefferson] ************************************** See what's free at http://www.aol.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
