On 2016-12-12 14:34, Paul Koning wrote:
On Dec 12, 2016, at 2:13 PM, Jacob Goense <d...@xs4all.nl> wrote:
I'm running simh in rather tight corners. Mostly VAX/780 and PDP-11/70
with V6 or BSD. Simh runs in a browser, or, I have (too) many of them
on underpowered Asus Eee PC's. Any tips on how I can check if I have
taken things too far?
Depends on what you mean by "too far". Do you want SIMH to run as
fast as, or faster than, the real hardware? If so, running, say, the
PDP11 simulator on a 780 is probably "too far". But it may be ok for
the 1620 emulator.
If by "too far" you mean "not useable", that depends on your
tolerance.
I don't mind if things run faster. In case a user runs into usability
issues I want to be able to gauge whether it is because simh is running
significantly slower than the real hardware or just time accurate.
People have run PDP-11 emulators on a PDP-10 (MIMIC).
There's a document describing an Electrologica X8 emulator that runs
on its predecessor the X1 -- a machine with no floating point hardware
and a typical instruction time around 50 microseconds. So the
emulation runs at about 4-8 ms per emulated integer instruction,
substantially slower for float. But it was (apparently) used for
initial development of substantial programs such as an ALGOL compiler.
It's all a question of what you consider reasonable.
For development purposes I'd run a pdp11 simh on a vax simh in a
browser, wait hours for it to get something done and find that more
than reasonable. Just that, when opening these Droste effects of
emulators in emulators in emulators in browsers to a wider public, I
want to be able to say that it is not that far off from the original
speed. I'm relatively young (from 1975) and lack the experience to
have even the faintest clue what these speeds are.
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