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=1.0 required=3.0 tests=BAYES_20,FROM_ADDR_WS autolearn=no autolearn_force=no version=3.4.5-pre1 Date: 16 Oct 92 23:14:52 GMT From: news.orst.edu!umn.edu!micro.cs.umn.edu!hansen@cs.orst.edu (David M. Hans en) Subject: Re: What is "real-time"? Message-ID: <1992Oct16.231452.12721@news2.cis.umn.edu> List-Id: Just to throw a wrench in things... Many people will define a real-time system in terms of its execution speed, e.g., "it must complete certain tasks before a deadline", or "an answer that is late is the wrong answer." These definitions aren't bad, but they leave out (what I consider) a critical component: an answer that's _early_ is just as bad as one that's late. Imagine a program sending data to a modem one characte r at a time. If the program loads the (single-character, in this example) transmit buffer _before_ transmission of the previous character has been completed, the data is mangled and the program has failed. Similarly, when receiving data, the program must react quickly enough to snatch each character from the receive buffer before the next incoming character over- writes it. Both components are critical. A better definition, I think (this is not original BTW), is that a real-time system must _manage_ time as a resource. Certainly, it must meet all its deadlines (I imagine that word has an interesting etymology), but also it must delay taking action on a calculation if that calculation completes before its answer is required. -=Dave