This time frame is also a bit off. The Dual Address Space architecture was first implemented via a microcode retrofit on the existing old 3033 hardware. It was not possible to make that hardware do I-Fetch from primary while running in secondary ASC mode, so the architecture had to state that the I-Fetch space was undefined while in secondary ASC mode, since the 3081 hardware was designed with the dual address space architecture in mind, and I-fetched from primary in both primary or secondary ASC modes.
Since the 3033 could not run XA, the 370/XA architecture was free to state that I-Fetching is done from the primary space in secondary ASC mode. ESA/370 and beyond does not always fetch from the primary space. It fetches from primary in Primary, Secondary, and AR, ASC modes. It fetches from home in Home ASC mode, and real in real mode (DAT-off). z/OS uses Home ASC mode only in code which is in common storage. Jim Mulder z/OS Diagnosis, Design, Development, Test IBM Corp. Poughkeepsie NY "IBM Mainframe Discussion List" <[email protected]> wrote on 11/18/2018 08:03:49 PM: > From: "Ed Jaffe" <[email protected]> > To: [email protected] > Date: 11/18/2018 08:42 PM > Subject: Re: System level coding examples > Sent by: "IBM Mainframe Discussion List" <[email protected]> > > On 11/18/2018 5:27 AM, Peter Relson wrote: > > PC-SS was introduced prior to MVS/XA (pre-1980) > > Data spaces were introduced with MVS/ESA (1987-ish), stacking PC's at the > > same time. > > We never used PC-ss prior to ESA/390 primarily because of a hardware > restriction that forced the code to always be in common storage (e.g. > LPA). ISTR it was undefined as to which address space your instructions > were fetched from when in cross-memory mode. You guys did the right > thing in ESA/390 by always fetching from the primary address space. In > addition, that old PCLINK STACK/UNSTACK stuff was horrible! ijs... > ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
