From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.5-pre1 (2020-06-20) on ip-172-31-74-118.ec2.internal X-Spam-Level: X-Spam-Status: No, score=-1.9 required=3.0 tests=BAYES_00 autolearn=ham autolearn_force=no version=3.4.5-pre1 Date: 17 Oct 92 15:18:52 GMT From: mcsun!uknet!yorkohm!minster!mjl-b@uunet.uu.net Subject: Re: What is "real-time"? Message-ID: <719335132.5132@minster.york.ac.uk> List-Id: In article <1992Oct15.153519.23717@fcom.cc.utah.edu> val@news.ccutah.edu (Val K artchner) writes: >I've given definitions of "real-time" from three different English language >dictionaries. Everyone seems to say that these are insufficient in a >computer science context. However, no one has actually posted an alternate >third-party definition of "real-time". I'll agree to use a formal definition >as given by the FAQ of the comp.realtime group (sight unseen). > >: Consider the following example. Suppose you are writing software for a >: missile system. Suppose you have a timing constraint where you must use >: a backup sensor if the main sensor does not respond every 25 msec. You >: cannot express such a constraint in C without using an OS call or an >: external routine. The C language has no real-time facilities per se. No-one seems to have spilt the real time issue into "hard real time" and "soft real time". The definition of hard real time I was given (in "Real Time Systems and Their Programming Languages", A. Burns and A. Wellings, Addison-Wesley) can be paraphrased follows: "A hard real time system is one where failure to respond within a given time is as bad as the wrong response" >Until we get a mutually agreeable third-party source (not biased toward >Ada nor C/C++), properly cited for reference purposes (and fairness to the >authors), then let's just "Stop the petty bickering!"* The Burns and Wellings book writes off C fairly early on, because it has no features for concurrency. Real-time and concurrency go hand in hand, and the authors provide a fairly convincing argument. Mat