Entropy cost of information

An entropy analysis of Szilard´s (1929) one-molecule Maxwell´s demon suggests a general theory of the entropy cost of information. The entropy of the demon increases due to the decoupling of the molecule from the measurement information. In general, neither measurement nor erasure is fundamentally a thermodynamically costly operation; however, the decorrelation of the system from the information must always increase entropy in the system-with-information. This causes a net entropy increase in the universe unless, as in the Szilard demon, the information is used to decrease entropy elsewhere before the correlation is lost. Thus information is thermodynamically costly precisely to the extent that it is not used to obtain work from the measured system