Edward E. Jaffe wrote: > That's a good question. Right now PSW keys 10-15 are (almost?) never > used for anything. Key 9 is used slightly in a somewhat kludgy manner. > > DOS/VS aka VSE/ESA aka z/VSE gives each "static" partition its own > storage key. This harkens back to the real-memory-only days when there > was one -- and only one -- address space. That's pretty much just old > baggage any more since the advent of dynamic partitions, which look a > whole lot like MVS address spaces.
MVS wasn't exactly immune from its real-memory-only, single address space heritage. Basically, (OS/VS2) SVS was MVT layed out in 16mbyte address space (AOS2 prototype for SVS was done on 360/67 with a little bit of low-level code for handling the page faults and CCWTRANS borrowed from cp/67 to do the virtual->real translation for CCWs). The transition to (OS/VS2) MVS really caused problems since the real-memory-only, common address space was institutionalized in the entrenced pointer-passing convention. It required the MVS kernel being (8mbyte) part of every (16mbyte) address space ... theoretically leaving only 8mbytes left for application. However, with the movement of various subsystems to their own (separate) virtual address space ... the common segment kludge had to be done allowing the pointer-passing paradigm to continue. Prior to 3033 dual-address space ... it wasn't uncommon to find large installations with 4-5mbyte common areas ... frequently leaving only 3mbytes (out of 16mbytes) for actual application use. Infrastructures that grew up with multiple virtual address spaces were heavily message passing based ... rather than pointer passing paradigm (which implied access in the same address space) dual-address space on 3033 and access registers in 370-XA were provisions for continued support of pointer-passing paradigm ... allowing the storage area being pointed at, to exist in a different (virtual) address space. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
