Newsgroups: comp.sys.amiga.advocacy
Subject: Re: Commodore and the Osborne Syndrome
From: lkoop@TIGGER.STCLOUD.MSUS.EDU (LaMonte Koop)
Date: 30 Jul 92 04:27:59 -0600
Reply-To: lkoop@TIGGER.STCLOUD.MSUS.EDU
Organization: St. Cloud State University, St. Cloud, MN

In article <1992Jul29.145948.6767@ctr.columbia.edu>, jerry@connection.prospect.com (Jerry Shekhel) writes:
>lkoop@TIGGER.STCLOUD.MSUS.EDU writes:
>>
>>AmigaOS was designed to be a fast, compact, and as close to real-time
>>OS as possible.
>>
>
>The fact that MP can't be done on a bare 68000 also *might* have had
>something to do with it.

Probably true on that point.  However, the concept of higher-level processors
was known to the OS early on.

>>
>>Anyone used to its good response time would be very
>>disappointed with its slowed reactions in a memory protected environment.
>>
>
>Oh, this is BS.  How much would it slow down the machine?  5%?  You wouldn't
>even notice that.  A slightly faster CPU would take care of the difference
>and then some.

Depends.  It is NOT B.S. as you put it.  The amount of slow-down would 
depend on the OS layout.  In the case of AmigaOS, response time is greatly
quickened by the use of shared resources - such resources would not be
possible in quite the same way under a memory protected environment.  While
only a modest slowdown might be apparent at a hardware level, the OS itself
will be affected in other ways.

>>
>>Seconds of all, applications presently would break, period, under
>>memory protection.  It simply is not an option under the current AmigaOS
>>layout.
>>
>
>You should have said so in the first place.  Sheesh, multitasking can't be
>added to MS-DOS, so they call it "braindead"; memory protection can't be
>added to AmigaDOS, so they call it "a design decision".  Give me a break.

MS-DOS is called 'brain-dead' for many more reasons than the lack of
multitasking.

>>
>>Memory protection is nice to have...I certainly enjoy it under 
>>large systems I have developed on.  As of yet, however, I have not seen an
>>implementation on a smaller system which did not noticably affect system
>>performance, in some cases annoyingly.
>>
>
>Oh please.  Name an OS which has been implemented both with and without
>memory protection on the same machine.  That would be the only way to make a
>fair comparison.  I'll tell you one thing, though -- SVR4 runs a hell of a lot
>faster on my 386 than did Minix, and guess which one has MP?

You have taken notice that implementation wise the internal design of an OS
will reflect upon its performance.  Minix is slower based on its internals
(not QUITE UNIX in nature), and the matter of memory protection has little to
do with the speed factor here.  As for an example of the type you mention, 
commercially you are correct...I don't believe there has been an OS implemented
both with and without memory protection.  However, in-house I have seen
modified OS's based upon different platforms (a good one was an OS/9 
derivation that was actually kinda cool once it was going) that were affected
at various levels by the addition of memory protection in terms of performance.
The OS/9 setup got about a 10-20% performance hit overall from the
modifications, and this was with heavy optimization.  Basically, this was due
to the need to remove any nice task shared resource setups which sped up the
beast (it wasn't EXACTLY OS/9 from the start...but close), or work them
out differently (which always turned out to be more roundabout and slower),
as well as the memory hit due to the MMU when a full table translation was
needed for any particular access (i.e., the address was not in the ATC). 
Plus the added handler code, etc... all contributed to the lower performance
levels.

>+-------------------+-----------------------+--------------------------------+
>| Jerry J. Shekhel  | Molecular Simulations | Time just fades the pages      |

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             LaMonte Koop -- SCSU Electrical/Computer Engineering
  Internet: lkoop@tigger.stcloud.msus.edu -OR- f00012@kanga.stcloud.msus.edu
               "You mean you want MORE lights on this thing???"
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