Bill Fairchild <[EMAIL PROTECTED]> wrote: > VSAM's being obsolete is like saying TSO is obsolete. VSAM has been > the strategic access method of IBM since the mid-1970s. It > underlies many other structures that programmers also don't see, > such as page data sets and catalogs, without which z/OS will not > run very well or long. A better term might be "non-obvious".
Page dataset I/O uses ASM's I/O driver, which adds new channel commands onto the end of "seldom ending channel programs" (SECP). MVS/XA added some extensions that allow suspension and resumption of channel programs. Originally, a new channel program for a page dataset volume forced ASM to end its own channel program (one outstanding channel program per subchannel). I'm not sure where that restriction fits into multiple channel programs per volume. The role "The Mysterious Media Manager" plays in VSAM and VSAM- like datasets is discussed in a NASPA article by Steve Pryor available at URL <www.naspa.com/PDF/2003/0503/T0305009.pdf> -- John R. Grout [EMAIL PROTECTED] ---------------------------------------------------------------------- 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
