With 64 bit machines, each processor now has 8K unique to it. Do they need to avoid the first 8K?
On Sat, Mar 7, 2020 at 7:25 AM Peter Relson <rel...@us.ibm.com> wrote: > > Answer: Not totally > > It is true that all current machines support page 0 in a data space, and > for them the "normal" origin returned would be 0. > That is not a guarantee that all future machines would have such support, > but I find it hard to believe any would not. > > However, we have found it highly desirable to avoid using page 0 of the > data space, in order to avoid ZAD events (which in turn make it more > difficult to spot ZAD errors). > The best way to do that is to use HideZero=YES on DSPSERV CREATE > (available since z/OS 2.1). And when that is done, the origin returned is > x'1000'. With HideZero=YES, any reference to the first 4K will fail, so > that you don't even need ZAD to find erroneous references. > > For us, best practice is to create a 2G data space (not 2G-4K), treat RC=0 > and RC=4 as OK, use HideZero=YES, and use an Origin of x'1000'. > > So you never really need to use the Origin keyword if you simply start at > x'1000'. There is a non-zero but miniscule risk if you assume that it is > OK to use an origin of 0. > > Peter Relson > z/OS Core Technology Design > > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, > send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN -- Mike A Schwab, Springfield IL USA Where do Forest Rangers go to get away from it all? ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
