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=0.8 required=3.0 tests=BAYES_50 autolearn=ham autolearn_force=no version=3.4.5-pre1 Date: 17 Oct 92 12:25:15 GMT From: news.encore.com!mpalmer@uunet.uu.net (Mike Palmer) Subject: Re: What is "real-time"? Message-ID: List-Id: hansen@micro.cs.umn.edu (David M. Hansen) writes: >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 i s >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 charact er 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. You definition is "interesting", but I'm not sure it's a definition that instantly says to someone who does not understand real-time, "Oh yes, now I see!". Regards, Encore Computer Corporation Mike palmer 6901 W Sunrise Boulevard 90 Layered Software Development Fort Lauderdale, Fl 33313 email: mpalmer@encore.com Telephone: (305) 797-2326