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From: robert@hslrswi.UUCP
Newsgroups: comp.unix.questions
Subject: Re: /dev/null: The final frontier
Message-ID: <608@hslrswi.UUCP>
Date: Wed, 27-May-87 09:28:54 EDT
Article-I.D.: hslrswi.608
Posted: Wed May 27 09:28:54 1987
Date-Received: Fri, 29-May-87 01:21:29 EDT
References: <100@upas.UUCP>
Reply-To: robert@hslrswi.UUCP (J. Robert Ward)
Distribution: world
Organization: Hasler AG, Berne, Switzerland
Lines: 53
Summary: /dev/null may generate entropy

In article <100@upas.UUCP> rcw@upas.UUCP (Robert White) writes:
>Some of these questions may be trivial. I've lost sleep over them:
>
>Where do the bytes go when moved or copied to /dev/null?
>Does the machine dissipate the data as heat?
>
>Robert White

The answer may just be yes. Seriously. In an article entitled
"Complexity and Transcomputability" in the book "The Encyclopedia
of Ignorance" (Pergamon Press, 1977), Hans J. Bremermann (apparently
then Professor of Mathematics and Biophysics at UCB) writes :

	Another kind of limitation to computation may be thermodynamic.
	R. Landauer (1961) has pointed out that when in the course of
	computation information is discarded, entropy is generated
	which must be dissipated as heat. How much information must
	be discarded when computations are carried out ?  Initially
	this question was not well understood. Recently Bennett (1973)
	has shown that any computation can be carried out essentially
	in a logically reversible way which implies that it can be done
	with little or no entropy generation (cf.  also Landauer, 1976).
	In Landauer and Woo (1973) both thermodynamic and quantum
	limitations are discussed and an extensive bibliography is given.
	There are many open questions.

	Bennett, C. H. (1973) - "Logical reversibility of computation",
		IBM J. Res. Devel., 17, 525-532.
	Landauer, R. (1961) - "Irreversibility and heat generation in
		the computing process" -  IBM J. Res. Devel., 5, 183-191.
	Landauer, R. (1976) - "Fundamental limitations in the computational
		process" - Bericht Bunsengesellschaft Physikal. Chem 80"
	Landauer, R. and Woo, J. W. F. (1973) - "Cooperative phenomena
		in data processing" - Synergetics, edited by H. Haken
		and B. G. Teubner, Stuttgart.


I doubt whether the bit bucket will ever fill up, but writing to
/dev/null may eventually cause your machine to overheat.


Cheers,
	- Robert.

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