On 12/01/2015 10:27 AM, Tom Marchant wrote:
On Tue, 1 Dec 2015 12:52:05 +0000, Bob Shannon wrote:
Amdahl responded by shipping some code that was loaded early in IPL to
accommodate the new instructions
SE and SP Assist. They trapped the abend in the FLIH. I remember it well.
That's SE Assist. And it led to the design on the 580 series of computers that
provided a third state of operation called (IIRC) System state. The 580 design
included hardware to virtualize the user's processor.
The code that ran in System state was called Macrocode and it was loaded
from the console processor into memory that was outside of the memory
available to customers. Macrodode routines emulated new instructions.
A side benefit of all that was that it made Multiple Domain Facility possible.
The hardware that supported the virtualization included additional registers for
the use of Macrocode and other facilities that made MDF quite efficient.
If I remember correctly, that led to FAM (a part of Macrocode),
Fast Assist Mode. It allowed Amdahl to emulate instructions
rather rapidly -- both on the machine and building the
instruction emulation to install on machines.
I do remember a very interesting thing that Amdahl did: MVCIN
It was implemented on those machines, but not on the IBM 3090s.
Which caused me a problem on a VSE to MVS migration, because I
needed that inverse move. When I was working at Amdahl I was
amazed at how that had been implemented.
I miss those days.
Regards,
Steve Thompson
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