There are two different issues. The free S/360 and S/370 operating systems require S/370 mode, as do the proprietary systems prior to XA and ESA. They use SIO, which does not exist in XA, ESA or z mode. Support for that disappeared earlier than support for XA and ESA.
-- Shmuel (Seymour J.) Metz http://mason.gmu.edu/~smetz3 ________________________________________ From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> on behalf of Mark S Waterbury <000001c3f560aac1-dmarc-requ...@listserv.ua.edu> Sent: Wednesday, September 9, 2020 1:35 PM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Re: Architectural Level Sets To add to this thread ... I would like to know at what point during the evolution from S/370 to S/370-XA to S/390 to zSeries, did the architecture stop supporting IPL of any OS that runs in "BC mode" or that starts out in BC mode, before setting up page and segment tables and control registers and then enabling DAT? In other words, what processor family(s) and specific models in that family, if need be, can no longer IPL and run any of the "public domain" operating systems from the 1970s to early 1980s? (DOS/360, OS/360, DOS/VS, OS/VS1, OS/VS2, VM/370, TSS/370, etc.) Thanks in advance. Mark S. Waterbury ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
