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From: james@phred.UUCP (JAMES Taylor)
Newsgroups: comp.realtime
Subject: Re: What is "real-time" really?
Message-ID: <2996@phred.UUCP>
Date: 27 Feb 90 21:42:38 GMT
References: <98692@linus.UUCP> <8140@pt.cs.cmu.edu> <1318@otc.otca.oz>
Reply-To: james@phred.UUCP (JAMES Taylor)
Organization: <1318@otc.otca.oz>o
Lines: 36

In article <1318@otc.otca.oz> gregw@otc.UUCP (Greg Wilkins) writes:
>Definition of "REAL TIME"?????
>
>Well I think that the answer "a system where the answer is wrong if it is
>late", is not correct.  This definition includes weather forcasting systems
>which must produce an answer in less than 24 hours (otherwise it is a 
>weather verification :-).
....
>
>"Real time systems are ones in which 'time' is an explicitly managed
>resource." - Author unknown.

This being the second article I've seen purpetuating the same fallacy,
I had to comment.  This is obviously a real time system.  It simply
is not a useful example of such a system, in the context of a discussion
of the special problems involved in a real time system design.

In the same way, boolean logic is not an apprioprate description until
the timing scale is such that you do not need to design in that infinite
analog inbetween.

Perhaps a useful extension of the defininition would be:

Real time systems are ones in which 'time' is a critically  managed
resource.                                       ^^^^^^^^^^

Time is clearly explicitly managed in the system example - However it was managed
via checkbook at the installation of the system, rather than by the designer
of the system specifically to provide management of time.

A real time system (as has been stated before) is characterized:

1) Management of processes parameterized in part by time
2) Ability to recognize that a process has failed to meet time requirements

James Taylor