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From: aglew@oberon.crhc.uiuc.edu (Andy Glew)
Newsgroups: comp.arch,sci.electronics,sci.physics,comp.lsi
Subject: Re: Electro-optic bus
Message-ID: <AGLEW.90Jul30150521@oberon.crhc.uiuc.edu>
Date: 30 Jul 90 20:05:21 GMT
References: <AGLEW.90Jul23203937@oberon.crhc.uiuc.edu> <1965@trlluna.trl.oz>
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In-Reply-To: aduncan@rhea.trl.oz.au's message of 27 Jul 90 06:32:12 GMT

>A laser might not be the best - they have a delay from zero curent while
>a population inversion is created.  Normally they are used with _varying_
>intensity rather than off/on, so there is added complexity, as well as
>the (current) need to edge couple to the fibre.  LEDs are better unless
>you want coherence.
>
>What you end up with is a pipeline, rather than a bus, maybe this will
>better match the current crop of pipelined CPUs :-)
>
>Overall, there is little, if any, advantage in electro-optic busses.  If
>it was all optic, then that might be different, but even then you are
>only talking pipes, as the trip time to an adjacent slot is significant.


So, what is the ballpark delay? Laser and/or LED?
Tens or hundreds of ns?


(I don't mean to be antagonistic. It's just that I've heard several
times "there is a delay", without anyone quoting even any order of
magnitude numbers).
--
Andy Glew, andy-glew@uiuc.edu

Propaganda:
    
    UIUC runs the "ph" nameserver in conjunction with email. You can
    reach me at many reasonable combinations of my name and nicknames,
    including:

    	andrew-forsyth-glew@uiuc.edu
    	andy-glew@uiuc.edu
    	sticky-glue@uiuc.edu

    and a few others. "ph" is a very nice thing which more USEnet
    sites should use.  UIUC has ph wired into email and whois (-h
    garcon.cso.uiuc.edu).  The nameserver and full documentation are
    available for anonymous ftp from uxc.cso.uiuc.edu, in the net/qi
    subdirectory.