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From: landman@SUN.COM (Howard A. Landman)
Newsgroups: sci.nanotech
Subject: Re: How big is a brain?
Message-ID: <8904180627.AA19451@athos.rutgers.edu>
Date: 23 Mar 89 19:57:57 GMT
References: <8903230413.AA09069@athos.rutgers.edu>
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In article <8903230413.AA09069@athos.rutgers.edu> shields@yunccn.UUCP (Paul Shields) writes:
>I've been told that the human brain has from 60 to 90 billion neurons.
>
>Problem 1: Design a chip to simulate a bunch of neurons.
>
>An estimate:  if we can simulate a neuron with a few thousand "circuits",
>we can probably simulate close to a hundred with the same circuits, since
>the transistors switch much faster than neurons react.  Assume that with
>100000 circuits (near the chip space of the 80286 processor,) we could
>simulate 1000 neurons in real time on one chip with current technology.
>Then we'd be talking on the order of 60 to 90 million chips (= 2^26) in a
>network, for each brain to be simulated.

I saw Carver Mead's talk at CompCon a few weeks ago.  He thinks this
approach is totally wrong.  Neurons operate using the raw physics of
their environment.  Simulating this digitally is horribly inefficient.
Consider simulating an 80286 using a digital computer.  The simulation
will run 2 to 7 orders of magnitude slower than the chip itself, even
though the underlying technology is identical!

A better approach (in Carver's view) is to use the device physics itself.
This requires very robust design techniques, which can adapt for bugs
in manufacturing.  Carver and his students have designed an artificial
retina using about 6 transistors per neuron-equivalent.  It has many
of the same properties that real retinas do - for example, it sees
after-images if it stares at things too long ...

The latest Intel chip has over 1,000,000 transistors.  Using Carver's
notions, that should be equivalent to at least 160,000 neurons.  Each
of these neurons is perhaps 10,000 times faster than a human neuron.
So, to get equivalent compute power to a human brain (assuming speed
can be traded off for size), we need ~80 G human neurons = 8 M machine
neurons = 50 chips.

Designing these 50 chips is an exercise left for the reader.

>Problem 2: How do we connect the chips?
>
>If, for example, we use Thinking Machines
>Corp's "Connection Machine" hypercube archetecture, presently around
>64K (=2^16) processors, We would have to hook up 1024 of those beasts.
>[a Connection Machine is more like a 4x4x4-foot cube. --JoSH]

That's at 16 neuron/chip.  At 160,000 neuron/chip, we would need 0.1 of
those beasts.  (We're going for the full ~80 G neurons here.) And 0.1 CMs
would be about 6 cubic feet, as big as a TV set.  Allowing for speed again,
we only need 0.000001 of those beasts; a single PC board.  Maybe even
room left over for a modem and MIDI out. :-)

>we'll see another order of magnitude change in the size of these things.)

5 chips.  One of the modules of HAL in 2001.

>Processor speeds should be approaching
>100 MHz at that time (assuming GaAs technology is delayed due to fabrication
>problems.)

For planning purposes (I want to enter the November 2000 International
Computer Go Tournament in Taiwan), I am assuming that a personal computer
in November 2000 will be ~100 MIPS, ~128 MB memory, ~1 GB disk.  The memory
and disk numbers may be too conservative, but I don't think I'll need more
than that.

	Howard A. Landman
	landman@hanami.sun.com