From: jerry@connection.prospect.com (Jerry Shekhel)
Subject: Re: Amiga 4000/Atari Falcon
Organization: Molecular Simulations, Inc.
Date: Fri, 28 Aug 1992 21:33:34 GMT
X-Posted-From: connection.prospect.com
X-Posted-Through: sol.ctr.columbia.edu

tsarna@endicor.com (Ty Sarna) writes:
>
>[realtime OS]
>
>It means the OS makes performance guaruntees and is guarunteed to behave
>the same under the same conditions for certain types of things. For
>example, on the Amiga the highest priority task(s) that are ready to run are
>always guarunteed to be run. A lower priority task will never run when a
>higher priority task is runnable. Other OSes handle this differently, to
>guaruntee that a runnable task always runs at least once in a while.
>That's not good or bad. That's a design tradeoff.
>

As far as I know, OS/2 always schedules higher-priority tasks before
lower-priority tasks.  So it meets this requirement.

>
>Realtime also means determinism. For example, there are very few VM
>systems that are realtime (there are a few, but they are relatively rare
>and OS/2 is not one of them). The reason for this is that a section of
>code can't be guarunteed to always take the same number of cycles to
>run under the same circumstance when the data or code memory that has to
>be accessed might have to be swapped in. The same code might take vastly
>different amounts of time to run depending on VM.
>

OS/2's VM can easily be disabled (MEMMAN=NOSWAP).  Nevertheless, I can't
see how either OS can guarantee anything about the amount of time it'll
take to execute a section of code.  After all, any process, no matter how
high its priority, will be pre-empted in favor of another process of equal
priority when its quantum expires, no?  Is it possible, in AmigaOS, to
designate a task as "non-preemptible"?  If not, there's no difference in
AmigaOS and OS/2 in this respect.

>
>It also usually implies that the OS is relatively low-overhead, and the
>task switch time is minimized (at the cost of some features)
>

Relatively low-overhead?!  Relative to what?  Remember, there are no
relatives; it's either real-time or it isn't -- your words.

>
>I merely pointed out a feature that the one OS has that yours lacks, and
>you attack me for that.  Do you know which system I use and/or prefer?
>Did you even bother to find out? No. Because I pointer out a difference,
>not even a better/worse difference mind you, but a simple difference in
>philosophy, I'm automaticly the enemy. Sheesh. And you called someone
>else paranoid? What does this say about you?
>

Hey, sorry I flew off the handle; bad day.  However, you really haven't
pointed out any real differences between the two OS's to justify your claim.

>
>Ty Sarna				           tsarna@endicor.com
>
--
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