Instructions come and--believe it or not--instructions go. I once read some doc on a newly introduced instruction. Don't remember the timeframe or the exact instruction, but it came with this interesting comment. This instruction, being new, will not cause a problem for existing code unless that code expects the instruction *not* to exist. In that case the new instruction will do something that the program does not expect. Right. One sort-of case occurred in JES2, whose error handling for 3900 printers had become increasingly convoluted to the point that the simplest short term 'fix' was to force a S0C1 abend and let JES2 internal error routines perform recovery using built-in code. This was accomplished by deliberately branching to an invalid 'instruction'. JES2 would clean up the printer and move on. Unfortunately, the APAR delivering this change branched to character data that looked like a packed decimal instruction. So instead of S0C1, the resulting S0C7 caused a JES2 abend. Not at all what was intended.
As for a vanishing instruction, I once wrote some code using the Move Inverse (MVCIN) instruction, which greatly simplified scanning data for a terminating character. Apparently MVCIN was introduced on the 4341 (?) but not carried forward to subsequent models. So S0C1. A rude shock for a clever programmer looking for ingenious solutions. . . J.O.Skip Robinson Southern California Edison Company Electric Dragon Team Paddler SHARE MVS Program Co-Manager 323-715-0595 Mobile 626-543-6132 Office ⇐=== NEW robin...@sce.com -----Original Message----- From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> On Behalf Of Seymour J Metz Sent: Tuesday, September 1, 2020 5:27 PM To: IBM-MAIN@LISTSERV.UA.EDU Subject: (External):Re: Architectural Level Sets CAUTION EXTERNAL EMAIL Well, a S/360 program that depends on getting PIC 06 for an unaligned load won't work correctly on a 360/85 or S/370. S/370 supported 2 KiB pages, and those are history. MVS/370 uses SIO, whch only exists in S/370 mode: also history. So carrying an old OS forward has always has issues. Sure, IBM could ensure absolute compatibiity for old releaes, but TANSTAAFL. Only IBM knows what the extra cost would be, but I guaranty that there would be an extra cost. I'm sure that this has been discussed at Share. -- Shmuel (Seymour J.) Metz http://mason.gmu.edu/~smetz3 ________________________________________ From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> on behalf of Tony Thigpen <t...@vse2pdf.com> Sent: Tuesday, September 1, 2020 5:20 PM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Re: Architectural Level Sets I was thinking more along the lines of things that prevented earlier operating systems from even IPLing on newer boxes. Such as z13 is the last processor to have ESA/390 mode. I also have it in my head that at some point there were changes to the page size and virtual storage tables that caused havoc. Tony Thigpen Seymour J Metz wrote on 9/1/20 3:30 PM: > Typically the new features reqiured by a level set were added over several > generations, and each generation added more than one feature. > > > -- > Shmuel (Seymour J.) Metz > http://mason.gmu.edu/~smetz3 > > > ________________________________________ > From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> on > behalf of Tony Thigpen <t...@vse2pdf.com> > Sent: Tuesday, September 1, 2020 3:25 PM > To: IBM-MAIN@LISTSERV.UA.EDU > Subject: Architectural Level Sets > > IBM has had several Architectural Level Set points where there were > significant changes to the CPU that prevented earlier operating > systems from running on them. > > What CPU's were involved with each level, and what was the real > underlying item changed on the CPU that forced a new level? (Let's > keep it limited to z990 and newer.) > > > Tony Thigpen > > ---------------------------------------------------------------------- > 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 > ---------------------------------------------------------------------- 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 ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
