Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!pt.cs.cmu.edu!fas.ri.cmu.edu!dstewart
From: dstewart@fas.ri.cmu.edu (David B Stewart)
Newsgroups: comp.realtime
Subject: Re: What is "real-time" really?
Message-ID: <8140@pt.cs.cmu.edu>
Date: 23 Feb 90 18:27:39 GMT
References: <98692@linus.UUCP>
Organization: Carnegie-Mellon University, CS/RI
Lines: 33

In article <98692@linus.UUCP> duncant@mbunix.mitre.org (Thomson) writes:
>
>Anyone care to comment?  What is the best definition of real-time?
>

By far the best definition I have seen about "What is real-time?" is
the following:

"A real-time system is one in which the correctness of the computations not
only depends upon the logical correctness of the computation but also upon
the time at which the result is produced. "  (original author unknown)

    E.g.  The computation 1 + 2 must be known by time t = 2 seconds, even
    if the answer of "3" arrives at t = 2.2 seconds, it is wrong because
    it is late! 

If the timing constraints of the system are not met, system failure is said 
to have occurred.  Hence, it is essential that the timing constraints of 
the system are guaranteed to be met.  Guaranteeing timing behavior requires 
that the system be predictable.  It is also desirable that the system attain 
a high degree of utilization while satisfying the timing constraints of 
the system.

Just like there is the monthly posting on comp.unix.questions of
Often-asked questions; there should be a monthly posting in this
newsgroup answering the question "What is Real-Time!" :-)


-- 
David B. Stewart, Dept. of Elec. & Comp. Engr., and The Robotics Institute, 
	Carnegie Mellon University,  email: stewart@faraday.ece.cmu.edu 
The following software is now available; ask me for details
        CHIMERA II, A Real-time OS for Sensor-Based Control Applications