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From: barmar@think.com (Barry Margolin)
Newsgroups: comp.arch
Subject: VAX and VMS development (was Re: Graphics Primitives)
Message-ID: <1990Nov21.191759.23254@Think.COM>
Date: 21 Nov 90 19:17:59 GMT
References: <11030@pt.cs.cmu.edu> <42992@mips.mips.COM> <513@ctycal.UUCP>
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Organization: Thinking Machines Corporation, Cambridge MA, USA
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In article <513@ctycal.UUCP> ingoldsb@ctycal.UUCP (Terry Ingoldsby) writes:
>Aren't you forgetting one of the most successful symbiotic relationships?
>I speak of VAX/VMS.  I took a VMS Internals course a few years ago, and
>was struck by the frequency with which the VAX architecture just happened
>to be exactly what was needed for VMS.  I finally concluded that if VAX
>was not designed for VMS, then certainly the hardware architects had a
>lot of input from the VMS people.  

Could you give examples?  While it's quite likely that you're right about
the hardware and software people talking to each other during the
development (if you're going to implement a proprietary OS specifically
targeted at your new hardware architecture, this is the right way to do
it), there are also other factors.  I don't know too much about VMS and VAX
internals, but I've never heard that it was extremely revolutionary.  The
VAX primitives are presumably based on the needs of timesharing systems
that were developed during the two decades before it was introduced, and
these OSes also strongly influenced the design of VMS.  In particular, it
was well known by then what hardware primitives are needed to support
efficient process scheduling and demand paged virtual memory.

Also, to contradict your premise, I have a vague recollection that the VAX
memory architecture is lacking a dirty bit in the page table (but I could
be confusing it with another contemporary), even though most paging
algorithms would be helped by this feature.  Perhaps the VAX and VMS seem
like such a good match because VMS doesn't try to do things that are hard
to do on the VAX.

--
Barry Margolin, Thinking Machines Corp.

barmar@think.com
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