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Path: utzoo!utgpu!water!watmath!clyde!rutgers!ll-xn!adelie!munsell!klm
From: klm@munsell.UUCP
Newsgroups: comp.sys.amiga
Subject: Virtual Memory vs. Real Time (was: Re: Wishlist for A3000)
Message-ID: <1390@atkins.munsell.UUCP>
Date: Thu, 19-Nov-87 09:47:21 EST
Article-I.D.: atkins.1390
Posted: Thu Nov 19 09:47:21 1987
Date-Received: Sat, 21-Nov-87 17:10:51 EST
References: <74@mithras> <1053@sugar.UUCP> <1382@squeaker.munsell.UUCP> <7730@g.ms.uky.edu>
Reply-To: klm@munsell.UUCP (Kevin [Being Weird Isn't Enough] McBride)
Organization: Eikonix Corp., Bedford, MA
Lines: 37
Keywords: VM != RT

In article <7730@g.ms.uky.edu> sean@ms.uky.edu (Sean Casey) writes:
>
>Where I work I do programming on a Masscomp 5500 running Real Time Unix
>version 3.0A.  RTU supports real time applications, and does it quite well,
>thus showing it can be done.  All one really has to do is give the user
>system calls to lock memory and a priority system that allows a process
>to take over the machine.

All I can say is that Masscomp must have made some really good improvements
to their Real Time Unix.  I haven't touched a Masscomp machine in over 3
years, but when I did, it was for high speed data acquisition.  RTU's
native facilities for doing Real Time stuff were completely inadequate.
In order to have the machine keep up with the data bus we ended up not only
having to dork with the system quite a bit, but we also had to write our
own disk driver that would do raw burst DMA without a filesystem.

I currently know of another situation with some friends of mine who are 
trying to do high speed data collection with a Sun 3 and they're going 
through the same nightmare.  Strip down the Kernel, no display, no file 
system, raw disk i/o at 10 tracks a whack, and they're barely cutting it.

In other words, yes, Masscomp, VAX/VMS, <whatever> will do realtime stuff,
but you have to dork with it so much that you end up wondering why you
ever bothered.  Why not start off with a 'real' realtime system and don't
expect it to do very much more than that.


The Amiga definitely needs memory protection to keep naughty programs from
being anti-social, but if you put VM on it, it's gonna be SLOOOOOOOOW!
The Sun/3 can cut it with VM because it's CPU goes about 3 times faster
than the Amiga.

-- 
Kevin McBride, the guy in the brace //       | It's the end of the world
Eikonix - A Kodak Co.              //        |   as we know it,
Billerica, MA                  \\ //  Amiga  | 
{encore,adelie}!munsell!klm     \X/   Rules! | And I feel fine...