Re: What is "real-time"?

[cis.ohio-state.edu!magnus.acs.ohio-state.edu!usenet.ins.cwru.edu!agate!do]

In article <1992Oct16.213820.28793@col.hp.com> tbc@col.hp.com (Tim Chambers) wr
ites:
>First I'll explain the approach which is used in our organization.  Rather
>than define "real-time" software, we break it into two categories:
>"time-sensitive" and "time-critical."  Time-sensitive software is that for




It somehow appears as if "time-sensitive" is rather irrelevant. I cannot
remember that I've ever seen a program that is not "time-sensitive" 
according to the proposed definition. And if all programs are "time-
sensitive", and some programs are also "time-critical", then this
distinction is of little use. 

I agree on the definition on the theme "a real-time task is a task whose
correctness rely on time constraints". I also find it probable that most
systems is a mix of real-time and other tasks. 

The distinction between "hard" and "soft" real-time is obscure to me. I
see two different explainations. 1) "Hard" real-time has fixed deadlines
while "soft" has statistical time constraints. 2) "Hard" real-time
systems are bought by someone that considers the proof of rate-monotonic
scheduling as magic ;) , and wants to see the scheduling of tasks in
a timing diagram, while "soft" real-time systems are ordered by a
customer that is satisfied if the system meets its deadlines, no matter
when in the allowed time-frame an individual task executes.

The latter explaination puts the classification of "hard" or "soft"
in the eye of the beholder (customer) rather than in the system itself.


      
                      Daniel W.



-- The above is my personal opinion
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--                                                                   --
-- Daniel Wengelin                                                   --
-- NobelTech AB    (Winner of the -92 Ada Industry Leadership Award) --
-- Naval Systems Division                                            --
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