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From: sims@stsci.EDU (Jim Sims)
Newsgroups: comp.sys.amiga
Subject: Re: Virtual Memory vs. Real Time (was: Re: Wishlist for A3000)
Message-ID: <114@mithras>
Date: Tue, 24-Nov-87 17:52:24 EST
Article-I.D.: mithras.114
Posted: Tue Nov 24 17:52:24 1987
Date-Received: Sat, 28-Nov-87 05:57:50 EST
References: <74@mithras> <1053@sugar.UUCP> <1382@squeaker.munsell.UUCP> <1390@atkins.munsell.UUCP>
Organization: Space Telescope Science Institute, Baltimore, MD 21218
Lines: 53
Keywords: VM != RT
Summary: Read your own text

In article <1390@atkins.munsell.UUCP>, klm@munsell.UUCP (Kevin [Being Weird Isn't Enough] McBride) writes:
<> 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.

   Agreed.

<> 
<> 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
<> 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 

 Let's be specific, what is "high-speed"? I've done ~56Kbyte data acquisition
and display and file creation on VAX 750 (~.7 MIP) under full VMS. No Problem.
Is that fast enough?

<> 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.
<> 

 Because some of us LIKE a REAL development environment.

<> 
<> 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.

 So, lets build an Amiga with a 68030, like I originally suggested!!!


 VM != SLOW

VM only provides a good means for running a program bigger than the memory you
have physically. There are several ways around paging problems, there is not
anything inherent in the concept of VM that precludes real-time.


-- 
            Jim Sims
            Space Telescope Science Institute
            Baltimore, Md. 21218
            sims@stsci.edu