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From: gustav@swanee.UUCP
Newsgroups: comp.sys.nsc.32k
Subject: Re: Question:  on-chip or off-chip MMU?
Message-ID: <327@swanee.OZ>
Date: Fri, 22-May-87 10:04:02 EDT
Article-I.D.: swanee.327
Posted: Fri May 22 10:04:02 1987
Date-Received: Wed, 27-May-87 02:02:20 EDT
References: <5635@shemp.UCLA.EDU> <441@prairie.UUCP> <319@crys.WISC.EDU> <579@gec-mi-at.co.uk>
Organization: El. & El. Eng., Uni. of Western Australia
Lines: 26
Summary: fine SF

In article <579@gec-mi-at.co.uk>, adam@gec-mi-at.co.uk (Adam Quantrill) writes:
> In article <319@crys.WISC.EDU> mcvoy@crys.WISC.EDU (Larry McVoy) writes:
> >
> >And this bit about optics?  Optics?  What will that buy you?  Sure light
> >travels fast but converting from electrons to photons is a drag.
>               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> So why bother? Have optical sensors on keyboards, direct light output on
> your terminal screen. All comms can easily be optical fibre. No need to convert
> optical disk information into electrical current. The only reason
> for converting between electrons & photons is interfacing to the old electron-
> driven computers.
>        -Adam.

Gee, this is a very nice piece of Science Fiction, but what has this
to do with on-chip or off-chip MMUs?
By the way, interaction of photons with photons (and that is needed to
process signals) is not a trivial matter. That's why photons are
being converted to electrons in most present day applications. That
conversion can be done very fast. The switching or signal processing
can be fast too. In fact the real drag in present VLSIs are 
metal connections between various nonlinear elements. If these could
be replaced with optical wave guides it would speed up the electronics
very significantly.

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