Setting up a VAXstation
ajp166 at bellatlantic.net
Mon Oct 8 07:42:57 CDT 2007
>Subject: Re: Setting up a VAXstation
> From: shoppa_classiccmp at trailing-edge.com (Tim Shoppa)
> Date: Mon, 08 Oct 2007 08:14:33 -0400
> To: cctech at classiccmp.org, cctalk at classiccmp.org
>Tony Duell said:
>> I cna understnad why people are interested only in old software, not
>> hardware, and want to run it under emulation on a modern machine
>> My puzzlement is with people who want to run the old hardware (not have
>> to run the old hardware becuase it is part of some machine tool or
>> something) but don't want to understand what's going on inside. What more
>> do you get over running the software under emulation?
>In fact, availability of hardware is a huge factor in succesfully
>making an emulator for a machine. All but the simplest processors
>are complicated enough that there are little corner cases all over
>the place where none of the processor/architecture documentation tells
>you what is going to happen.
>And outside the central processors, all peripherals but the very simplest
>are filled with complicated and undocumented behavior.
>Schematics could answer many of these questions, but in real life
>they end up guiding the search for the answer to the question rather
>than being the actual defining source for the answer.
>So in general emulator users and especially developers completely
>grok the need to have hardware working. Sometimes I believe that
>today's emulator developers know much more about the architectures
>than the original architects did :-). (In a couple cases, they are
>the orignal architect!)
>Availability of software is also important for making a reliable emulator.
>You could spend years reading the books to write an emulator, but you
>don't trust anything you've read or done until you've booted the simplest
The best example of this that comes to mind is the Apollo Guidence
Computer (AGC). There was one hardy and persistant soul that not
only researched it, he built a sim and tracked down samples of
software to validate the sim and the later hardware. One great
issues was lack of documentation, apparently much was lost/destroyed
when that chapter of the space program ended around 30 years ago.
The few intact copies of the AGC (Apollo command modules) likely
haven't seen power in at least that long if even complete. I doubt
any of the CM holders could be convinced to power it up assuming
they were even preserved sufficiently to safely do so. So for
those interested in machines that are obscure, unusual or very
rare even generating a sim has to be a huge challenge only equaled
by task of gatherering the needed data to base it on. It is reverse
engineering on a very deep level for a faithful sim.
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