<snip> 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 </snip> It depends how much earlier you are thinking of. A z/OS prior to OS/390 R10 would not work on a machine that is z/Arch-only. A z/OS prior to z/OS 1.12 would not work on a machine that begins the IPL in z/Arch mode.
I don't happen to know what about the z990 would have caused an earlier release of the OS not to work. In almost all cases, an old enough OS (specifically, one for which toleration support for a new machine was not provided) will not work properly because there are machine-related definitions that need to be accommodated and those would not have been provided. But it might well IPL. Peter Relson z/OS Core Technology Design ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
