On Thu, 29 Aug 2019 19:56:57 -1000, Anne & Lynn Wheeler wrote: >in the wake of the FS faulure (FS was going to be completely different >than 370, and 370 efforts were being shutdown during FS period, also >lack of 370 offerings during FS period is credited with giving clone >mainframe vendors market foothold), there was mad rush to get stuff back >into 370 product pipeline ... 303x and 3081 Q&D efforts were kicked off >in parallel. 3081 included 370/xa, 31bit addressing and "access >registers" (subsystems had their own virtual address space, but could >use "access registers" to access "parameter" storage in application >address space). All this was known informally as "811" for the Nov1978 >publication date of the architecture specification documents.
I don't know about IBM internal plans or discussions, but Access Registers and AR mode were not publicly announced as part of 370/XA. They were first documented in the Enterprise System Architecture/370 Principles of Operation, SA22-7200-0, which can be found at http://bitsavers.trailing-edge.com/pdf/ibm/370/princOps/SA22-7200-0_370-ESA_Principles_of_Operation_Aug88.pdf Appendix D of that manual describes differences between 370-XA and ESA/370. On page D-1 it has this: <quote> New Facilities in ESA/370 The following facilities are new in ESA/370 and are not provided in 370-XA. Access registers, home address space, linkage stack, and load and store using real address are provided by all ESA/370 models. Move with source or destination key and private space are provided by some ESA/370 models. </quote> > >In part because of the increasing threat of CSA increasing to 8mbytes >for larger 3033 customers, a subset of "access registers" was >retrofitted to 3033 as "dual-address space" mode ... subsystems could >have their own address space, but also a 2nd address space to access >calling application parameters directly ... w/o needing CSA space. > >In 370 (3033) dual-address space mode ... there still wasn't program >call, but a supervisor call which in software would move the application >space address space to secondary and then load the subsystem address >space and enter the called subsystem. In 370/xa and "access register" >program call had a system defined table with all the necessary >information to do that function directly as part of the program call >instruction (whether implemented in hardware, microcode, picocode and/or >some combination) To clarify a bit, there was no Linkage Stack until ESA/370, and hence no stacking PC. -- Tom Marchant ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
