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From: roberts@icst-ecf.arpa
Newsgroups: comp.unix.questions
Subject: bits to /dev/null, and dissipationless computing
Message-ID: <7505@brl-adm.ARPA>
Date: Thu, 21-May-87 17:25:01 EDT
Article-I.D.: brl-adm.7505
Posted: Thu May 21 17:25:01 1987
Date-Received: Sat, 23-May-87 12:36:44 EDT
Sender: news@brl-adm.ARPA
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A few years ago, an article was circulated pertaining to the question
of whether or not it is theoretically possible to construct a device
which performs computations with zero net dissipation of energy.
The basic premise was that changing the value of a binary logic element
always requires a change in energy level, and that quanta of energy
are pumped around in a manner somewhat analogous to the operation of
a heat engine. In one of the models described, the possibility of
dissipationless computing requires that a certain relationship exist
between the initial state and the final state of the processor; thus,
the proper handling of any unneeded bits of information becomes vitally
important. 

We could never figure out whether the article was serious or not. 

(For real-world applications, this will not be a problem
until the development of the peanut-sized Cray-97, for which the
dissipation of any measurable amount of energy per operation would
vaporize both the processor and the surrounding building.)

                                     John Roberts
                                     roberts@icst-ecf.ARPA

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