On Sun, Jan 29, 2012 at 04:30:38PM +0100, Evgenii Rudnyi wrote:
> The problem that I see is that the entropy changes when the
> temperature changes. Or do you claim that the entropy of the memory
> stick/DVD/hard disc remains the same when its temperature changes
> for example from 15 to 25 degrees?

The entropy changes.

> Anyway, I do not see how one can obtain the information capacity of
> the storage devices from the thermodynamic entropy and this is my
> point.

Who was ever claiming that? The theoretically maximum possible
information storage is related, though.

> Do you claim, that the information capacity for which we pay money
> of a memory stick/DVD/hard disk is equivalent to the thermodynamic
> entropy of the device?

Never. The best you have is I=S_max-S, where I is the theoretical
maximum possible information storage. The value C (capacity of the
storage device) must satisfy

C <= I.

Usually C << I, for technological reasons. Also, it is undesirable to
have C vary with temperature, whereas I does vary in general
(particularly across phase transitions).

The information content of a drive is another number D <= C, usually
much less, and very dependent on the user of that drive. If the drive
is encrypted, and the user has lost the key, the information content
is close to zero.

The quantities I, C and D are all numerical quantities having the name


Prof Russell Standish                  Phone 0425 253119 (mobile)
Principal, High Performance Coders
Visiting Professor of Mathematics      hpco...@hpcoders.com.au
University of New South Wales          http://www.hpcoders.com.au

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