Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83; site wateng.UUCP Path: utzoo!watmath!watdaisy!wateng!padpowell From: padpowell@wateng.UUCP (PAD Powell[Admin]) Newsgroups: net.arch Subject: Re: Cray vs ICs, continued Message-ID: <88@wateng.UUCP> Date: Wed, 15-Jun-83 08:12:39 EDT Article-I.D.: wateng.88 Posted: Wed Jun 15 08:12:39 1983 Date-Received: Thu, 16-Jun-83 06:59:33 EDT References: <3018@utzoo.UUCP> Organization: U of Waterloo, Ontario Lines: 27 The whole area of high performance digital logic borders on black art, with a healthy dab of applied mathematics, mechanical engineering, and love of experiment. For instance, if you send a signal down a line, it will keep on going until it comes to a discontinuity. Whereupon really ugly things will happen. The usual analogy is that of a wave in a bathtub. Start the wave at one end, and watch what happens as it hits the other: reflections, etc. To keep this crud to a minimum in electronic circuits, it is neccessary to terminate a line with the same impedance. Lines are usually designed to be purely resistive, so terminating them with a resistor is called for. Now think about all those little chips, about 3mm across, needing all those huge resistors... So the cunning chip designers put the resistors on the chip, making the chip slightly larger, and increasing its power consumption. Unfortunately, this is only the first step. Due to other problems, it is usually not possible to run a single line for a signal. It becomes neccessary, for distances over about 4 inches, to use two lines, and drive them differentially. The design of the hardware for this monster has to be seen to be believed. Strangely enough, I have the feeling that it is one of the last areas to be impacted by the CAD market... After all, who would invest the hundreds of man years neccessary to design a system which would automatically lay out a board? Answer: IBM, Japan Inc., ITT, and other people... Hot topic for people interested in wierd and wonderful CAD applications. Patrick Powell, U. Waterloo