The following message is a courtesy copy of an article that has been posted to bit.listserv.ibm-main,alt.folklore.computers as well.
[EMAIL PROTECTED] (Hunkeler Peter , KIUK 3) writes: > Fixed storage is not only to support diabled users but much more often > used in the ubiquituos I/O processing. The channel subsystem (the I/O > part of System z hardware) does not use DAT. Channel commands transfer > data blocks data from and to real storage to and from I/O devices, > resp. Before the I/O can be initiated, MVS's I/O supervisor code has > to make sure the virtual storage allocated for the I/O buffers is not > being paged out while the channel subsystem is working on the I/O > request. Therefore, the pages will be fixed before the I/O supervisor > passes the I/O request to the channel subs this was part of the technology that was borrowed from cp67 in the original os/vs2 work ... discussed earlier in this thread http://www.garlic.com/~lynn/2007p.html#69 GETMAIN/FREEMAIN and virtual storage backing up http://www.garlic.com/~lynn/2007p.html#70 GETMAIN/FREEMAIN and virtual storage backing up one of the uses for "fixed" storage was allowing applications to build channel programs with the (previously) "fixed", real storage addresses ... then the application channel program could be directly executed ... w/o requiring the supervisor having to scan ... building a shadow/duplicate channel program with the "real" addresses for instance, lookup various discussions about EXCPVR compared to EXCP ... this redbook has some discussion of the differences between EXCPVR and EXCP (although most of the discussion is about support for using storage about 2GB line) http://www.redbooks.ibm.com/abstracts/SG245976.html from 2.10.3 Using EXCP and EXCPVR Programs using EXCPVR have the esponsibility to page fix all I/O area and build real channel programs. ... snip ... ---------------------------------------------------------------------- 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
