[email protected] (David Andrews) writes: > I vaguely remember the dual-address-space-facility that began life just > before XA came around. There was some exploitation of it in - I think - > MVS/SE2 (or was it SP1?).
in the wake of the failure of FS http://www.garlic.com/~lynn/submain.html#futuresys ... they kicked off 3033, 3081 & xa-architecture approximately concurrently http://www.garlic.com/~lynn/2014d.html#54 Difference between MVS and z / OS systems but the extensive pointer passing api and need to map common address ... by late in 3033 period, the combination of mvs kernel and common segment (morphed into common system area) was on the verged of taking up all the area in the 16mbyte virtual address space given to each application for execution. One of the people that was involved in XA, the (aborted) effort to use 801/risc (Iliad chip) as the microprocessor for low & mid-range 370 ... do a retrofit of a subset of XA multi-address space addressing to 3033 as dual-address space mode ... as a way of trying to take some pressure off the need for the constant growth in common system area size (for passing parameters between address spaces). dual-address space mode allowed semi-privileged subsystem to access parameter list in calling application parameter list ... w/o it having to be in the common system area. he was working on 801/risc Iliad chip right up until the time he left for HP Labs ... where he worked on the HP risc chip (snake) used in their line of machines. He then was the lead architecture (at HP) on the architecture for Itanium. shortly after he left for HP Labs ... I was getting email asking if I was going to join him. past posts mentioning 801, risc, iliad, romp, rios, power, power/pc, etc http://www.garlic.com/~lynn/subtopic.html#801 the other problem that mvs had in the 3033 time-frame was that it not only was in danger of taken up the whole 16mbyte virtual address space ... but its really bloated implementation was starting to overwhelm 16mbyte real storage limitation. Besides dual-address hack for 3033, another hack was rasing real storage to 64mbytes ... even though there was only 24bit addressing. There was two unused bits in the 16bit page table entry (that mapped a virtual page number of real page number). The hack was to prepend the two unused bits to the existing 12bit page number allowing addressing up to 64mbytes (the 12bit virtual page number mapped into a 14bit real page number). It wasn't possible to directly address any of the storage about the 16mbyte line ... except via virtual page number. Fortunately for I/O there was IDAL ... originally introduced in 370 to handle a problem with overruns involving non-contiguous page crossing i/os (360/370 channel architecture precluded prefetching of CCWs so data-chaining could sometime overrun since it had to wait for the i/o transfer on the previous ccw to complete before it could fetch the following ccw ... IDALs lifted that restriction allowing all addresses in IDALs to be prefetched). In any case the IDAL field was 32bits ... allowing I/O transfer addresses in the greater than 16mbyte area to be addressed. Especially in vm370 ... when virtual machine data in a virtual page above the 16mbyte line needed to be addressed ... it had to be brought down below the line. There original approach was to write the page to disk and then read it back in below the line. I provided them with a hack using dummy page table entries where a MVCL in virtual mode could bring the page down below the line (w/o resorting to in/out page i/o). as an aside, in the wake of the FS failure, POK kicked off 3033, 3081, and XA architecture. At the same time, Endicott kicked off 138/148, 138/148 ECPS ... mentioned here: http://www.garlic.com/~lynn/2014d.html#59 Difference between MVS and z / OS systems the 4331/4341 and E-architure. The 4331/4341 was approx. mid-range analogy to the 3081 ... except it was all brand new technology and finished much faster than the use of the warmed over FS technology for 3081 ... discussed here: http://www.jfsowa.com/computer/memo125.htm The E-architecture for DOS/VS and VS1 was sort of the low/mid-range analogy to XA architecture for MVS. However, its primary feature was moving much of the single virtual address space operation into microcode. DOS/VS (virtual dos/360) and VS1 (for os/360 mft) did something similar that OS/VS2 SVS did ... map the real kenel operation into single virtual address space ... sort of like emulating a large real memory machine. E-architecture moved a lot of what was the 370 virtual pagetables into the microcode layer. However, the big explosion in 4300 machines were with vm/370 ... which required separate (370) virtual address space for each virtual machine ... and so E-architecture didn't catch on like XA did (although you see its influence in the "name" VSE). Another 4341 issue was that they were out in late 70s, overlapped with 3033 and well before 3081. Cluster of vm/4341s had more processing power than 3033, larger aggregate memory than 3033, high aggregate i/o than 3033, and much less expensive (and more cost/effective) than 3033. While lots of 4300s were publically positioned as competition to other mid-range like DEC VAX ... POK 3033 also felt the competitive heat, and at one point the head of POK managed to have the allocation of a critical 4341 manufacturing component cut in half. some old 4300 email http://www.garlic.com/~lynn/lhwemail.html#43xx other posts in this thread: http://www.garlic.com/~lynn/2014d.html#55 Difference between MVS and z / OS systems http://www.garlic.com/~lynn/2014d.html#56 Difference between MVS and z / OS systems http://www.garlic.com/~lynn/2014d.html#57 Difference between MVS and z / OS systems http://www.garlic.com/~lynn/2014d.html#60 Difference between MVS and z / OS systems http://www.garlic.com/~lynn/2014d.html#61 Difference between MVS and z / OS systems -- virtualization experience starting Jan1968, online at home since Mar1970 ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
