On 29.01.2012 23:00 Russell Standish said the following:
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

What are S_max and S in this equation?

Evgenii

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 information.

Cheers

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