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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