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From: hrubin@pop.stat.purdue.edu (Herman Rubin)
Newsgroups: comp.arch
Subject: Re: 64-bits, How many years?
Summary: Can this type of efficiency be obtained?
	What is the effect on speed?
Message-ID: <8329@mentor.cc.purdue.edu>
Date: 20 Mar 91 13:18:34 GMT
References: <1991Mar19.225915.17474@sj.nec.com>
Sender: news@mentor.cc.purdue.edu
Lines: 39

In article <1991Mar19.225915.17474@sj.nec.com>, koll@NECAM.tdd.sj.nec.com (Michael Goldman) writes:
> 
> Back in Feb. '91 bill davidsen posted a comment to the effect that the limits
> of trace size, electron size, and photon size would mean 64 bits address
> size would be all we'd ever need - because we couldn't use any more than that.
> Others commented about the need for large virtual spaces but this is to mention
> some ways around the limits.
> 
> I read sometime in the last 6 months that a research group (AT&T or one of
> the other giga-companies) was working on using the energy state of the
> electrons of an atom as a way of storing information.
> 
> I.e., since an electron can be at any of a large number of energy levels, which
> can be induced by sending a photon to the electron, then the energy level of
> the valence electrons would be one-to-one mappable to numbers.  So, if one
> atom could have 8 easily manipulated energy states, two atoms could represent
> numbers 0-63, 4 atoms could represent (8 * 8 * 8 * 8) 0-4095, etc.

		[More details of the same type.]

There are real problems with this.  The uncertainty principle also requires
that if the energy is precisely known, the time cannot be.  If we want very
high switching speeds, and we need precision, do we not need enough particles
to keep the uncertainty principle from overwhelming things?  Also, how about
spontaneous emission of radiation?

Furthermore, if one sends a photon to an electron, one cannot be sure what
will happen.  The probability distribution of results is rarely simple.  
An energy high enough to cause the desired transition to be reasonably
likely is high enough to cause unwanted transitions with good probability.
The way out is redundancy, but there goes the efficiency.

All present memory devices to my knowledge, except those causing permanent
changes on a write, use an inefficient hysteresis loop.  It is this 
thermal inefficiency which allows reliable storage.
--
Herman Rubin, Dept. of Statistics, Purdue Univ., West Lafayette IN47907-1399
Phone: (317)494-6054
hrubin@l.cc.purdue.edu (Internet, bitnet)   {purdue,pur-ee}!l.cc!hrubin(UUCP)