X-Message-Number: 25987
Date: Fri, 8 Apr 2005 10:36:50 -0400
From: Thomas Donaldson <>
Subject: To Pat Clancy, re parallel computers

To Pat Clancey, re computers:

Believe it or not, when I was in the computer industry my specialty
was programming parallel computers. (I left the industry not 
deliberately but because I came down with a brain tumor --
an astrocytoma, which made keeping an ordinary job hard if not
impossible, for practical reasons).

However you wish to define an "algorithm", I will point out one
major feature of parallel computers of the kind that consist of 
separate single computers communicating with one another: it's
quite possible for every single computer on the net to be doing
something different from any other one, and ALL simultaneously.
And TIME makes a big difference in real life. If one processor
fails to get needed information from others at the time it 
needs it, the system can collapse.

Yes, when we humans program such computers we try hard to avoid
such a situation. In fact, one line of engineering such parallel
computers works hard to make them look to the user as if they
are a single computer. However no one yet goes about programming
brains, which are NOT put together that way. Among other things
done with parallel computers is to design them and their message
passing so that they can stop and wait for messsages which 
have not yet arrived. Yes, this can slow things down a bit. 

Think, though, of what you do when you're walking on a road 
and it looks like a car will hit you. A lot of your neurons 
work together to get you to move out of the way, and they all
work simultaneously while doing different things. Your neurons
have learned the "algorithm" of getting out of the way so
that they can work all at once, simultaneously, to MOVE YOU.
So far as I know, no one has really attempted to do such 
a fine programming of any computer --- instead they use
the methods I describe (very briefly) in the previous paragraph.

And that's the difference, and why I said there was a difference.

           Best wishes and long long life to all,

               Thomas Donaldson

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