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From: boylan@spectacle.sw.stratus.com (Richard Boylan)
Newsgroups: comp.os.aos
Subject: Re: DG/UX on an MV/20000???
Message-ID: <3915@lectroid.sw.stratus.com>
Date: 24 Jan 91 17:44:23 GMT
References: <28117.279dbffe@kuhub.cc.ukans.edu>
Sender: usenet@lectroid.sw.stratus.com
Reply-To: boylan@spectacle.sw.stratus.com (Richard Boylan)
Organization: Stratus Computer, Inc.
Lines: 48

In article <28117.279dbffe@kuhub.cc.ukans.edu>,
brownrigg@kuhub.cc.ukans.edu writes:
|>(this isn't exactly the right news group, but its as close as they come...)
|>
|>Can anybody share their experiences with DG/UX running under the MV
|>architecture?  It was indicated by the local people that Unix and the MVs
|>were a very poor match, and that performance was atrociously slow.  I hope
|>this isn't true!  What would be peculair about the MV arch. that would
|>promote this?
|>
|>Thanks
|>
|>Rick BRownrigg
|>Kansas Geological Survey

I didn't work on DG/UX too much, but I did port some of the system
software to it.  Some of the reasons I can think of why the MV
architecture would be unfriendly to Unix:

 * The MV architecture, like all Data General proprietary architectures,
	has a different format for byte pointers and word pointers.
	Changing from one to the other involves a shift right or left
	by one bit.  Software that is less that impeccable in its
	pointer typing will invariably not run without some work.
 
 * MV stacks grow upward, while Unix has a bias towards downward-
	growing stacks.

 * With only four registers, programs that were carefully tuned to
	run well with 8 or 16 registers ran terribly.

 * DG's own C compiler was pretty much the only C compiler available.
	The merits of this compiler have already been discussed here.
	But suffice to say that while it was one of DG's best proprietary
	compilers, it was not comparable to state-of-the-art C compilers.

 * Other tools like assemblers and linkers were ported AOS/VS tools,
	and any similarity between them and the generic Unix tools
	was minimal.

To its credit, DG/UX did have some points in its favor. For example,
I was told that it was one of the first decent implementations of
demand-paging for UNX.  But as I said, I did not use it much.  Perhaps
other DG alumni can say more.

Richard Boylan
Stratus Computer
boylan@spectacle.sw.stratus.com