On Tue, 2 Mar 2021 16:35:46 +0000, Seymour J Metz wrote: >For best performance, NCP should match the number of DECBs you allocate and >you should do a READ on each of them. If real storage is an issue, reduce that >number appropriately. When you hit EOF (EODAD is entered), stop issuing READ. > (Decades old experience:)
Of course, if the programmer is coding for overlapped I/O, the access method may be unable to detect EOF before the program has issued several more READs. MVS BSAM somehow handles this correctly: READs beyond EOF just don't happen. CMS/XA OS emulation was terrible. READs were synchronous: control did not return to the caller until channel/device end and DECB was posted. Additional READs intended to be asynchronous read garbage data or got I/O errors. I used the same code on both OSes. -- gil ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
