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From: ds@hollin.prime.com
Newsgroups: comp.ai
Subject: Re: Building a brain
Message-ID: <83500001@hollin>
Date: 16 Oct 89 20:13:00 GMT
References: <5259@ubc-cs.UUCP>
Lines: 35
Nf-ID: #R:ubc-cs.UUCP:-525900:hollin:83500001:000:1655
Nf-From: hollin.prime.com!ds    Oct 16 16:13:00 1989


In "The Connection Machine" (MIT Press, 1985), W. Daniel Hillis writes, "As
near as we can tell, the human brain has about 10**10 neurons, each capable of
switching no more than a thousand times a second.  So the brain should be
capable of about 10**13 switching events per second.  A modern digital
computer, by contrast, may have as many as 10**9 transistors, each capable of
switching as often as 10**9 times per second.  So the total switching speed
should be as high as 10**18 events per seconds, or 10,000 times greater than
the brain.
. . .
One reason that computers are slow is that their hardware is used extremely
inefficiently.  The actual number of events per second in a large computer
today is less than one-tenth of one percent of the number calculated [above].
The reasons for the inefficiency are partly technical but mostly historical.
. . .
In a large von Neumann computer almost none of its billion or so transistors
do any useful processing at any given instant.  Almost all of the transistors
are in the memory section of the machine, and only a few of those memory
locations are accessed at any given time.
. . .
This is called the von Neumann bottleneck.  The bigger we build machines, the
worse it gets.
. . .
The obvious answer is to get rid of the von Neumann architecture and build a
more homogeneous computing machine in which memory and processing are
combined.
. . .we have the existence proof of the human brain, which manages to achieve
the performance we are after with a large number of apparently slow switching
components."

Hope this helps.

David Spector
Prime Computer, Inc.
ds@primerd.prime.com (until the layoff)