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From: moscom!bmt!tvf@cs.rochester.edu (Thomas V. Frauenhofer)
Newsgroups: comp.os.research
Subject: Re: Real Time Operating Systems
Message-ID: <5331@saturn.ucsc.edu>
Date: 31 Oct 88 20:10:39 GMT
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In article <5276@saturn.ucsc.edu> masscomp!fdr@swan.ulowell.edu (Franklin Reynolds) writes:
>
>Most of the research in real time that I have read about focuses on
>trying to guarantee that all the deadlines can be met. This seems to 
>me like trying to guarantee program correctness. It is a laudable,
>though probably unabtainable goal, except in trivial cases. It seems to
>me that when you start working on big problems, like the space station,
>you have to assume that you will occasionally have overload conditions.
>If this is true then you need a strategy that allows you to gracefully 
>degrade in the face of overload. Comments?

Indeed, there are 2 "strains" of real-time systems: hard and soft.  Hard
real-time systems are what you define; soft real-time systems allow for some
deadlines to be missed (within some error range) as long as missing a deadline
will allow the overall system time specifications to be close.

Remember, time deadlines are the raison d'etra of real-time systems.  We want
guaranteed, repeatable performance every time.

>
>Another thing about most real time research is that most people seem to
>treat deadlines as all or nothing situations.

Depends on what are the results of missing a deadline.  Some are fatal; some
aren't.

You might want to leaf through the proceedings of the IEEE Conferences on
Real-Time Systems.

>Franklin Reynolds
>harvard!masscomp!fdr
>fdr@masscomp.uucp
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