Newsgroups: comp.arch
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Surges
Message-ID: <1989Nov19.030643.28335@utzoo.uucp>
Organization: U of Toronto Zoology
References: <503@ctycal.UUCP> <15126@haddock.ima.isc.com> <7000@pt.cs.cmu.edu> <150@csinc.UUCP> <17067@dartvax.Dartmouth.EDU>
Date: Sun, 19 Nov 89 03:06:43 GMT

In article <17067@dartvax.Dartmouth.EDU> jskuskin@eleazar.dartmouth.edu (Jeffrey Kuskin) writes:
>[Cray 1] "...The other part of the solution is to
>use only simple gates and make sure that both sides of
>every gate are always terminated.  This means that there
>is no dynamic component presented to the power supply."

In case anyone is curious, the significance of the "simple gates" part is
that in the ECL technology used, simple gates have differential inputs and
differential outputs.  (Each logical bit is carried by two wires, one the
inverse of the other.)  So any time one wire is swinging from 0 to 1, its
mate is swinging from 1 to 0, and any difference in power consumption is
cancelled out.  The larger chips use non-differential signals internally
(to simplify chip layout) and externally (to conserve pins) and so this
can't be done with them.
-- 
A bit of tolerance is worth a  |     Henry Spencer at U of Toronto Zoology
megabyte of flaming.           | uunet!attcan!utzoo!henry henry@zoo.toronto.edu