Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!henry From: henry@utzoo.UUCP (Henry Spencer) Newsgroups: net.arch Subject: Cray vs ICs, continued Message-ID: <3018@utzoo.UUCP> Date: Tue, 14-Jun-83 15:50:24 EDT Article-I.D.: utzoo.3018 Posted: Tue Jun 14 15:50:24 1983 Date-Received: Tue, 14-Jun-83 15:50:24 EDT Organization: U of Toronto Zoology Lines: 28 A friend of mine objected to one statement I made in my recent note about why Seymour Cray doesn't use nontrivial ICs. His objection, and my comments in reply, may be of interest as an expansion on my earlier note: ----- What do you mean "line termination within IC's". There's no such thing. When you're sending a signal 3 millimetres across a chip, you don't need to terminate it. Signals between chips still need to be terminated at the chip, of course. ----- What do I mean "line termination within IC's"? I haven't the foggiest idea. It sounds a bit odd to me too. I am more-or-less quoting from an article in IEEE Computer, and it's possible that the writer got his facts wrong. But I'm not Seymour Cray, and I do know he has problems far beyond those that mere mortals encounter. He needs proper line characteristics for reasons above and beyond avoiding reflections -- the power demand from his ICs must be as close to pure DC as possible, because he'll get standing waves in his ground planes if the power demand is switching in time with the clock signals. This is just as important a reason for using differential pair everywhere, and may account for his objections to MSI (it's been a while since I read the article in question). Henry Spencer U of Toronto