  Starting from Landauer's slogan "information is physical," we revise and
modify Landauer's principle stating that the erasure of information has a
minimal price in the form of a certain quantity of free energy. We establish a
direct link between the erasure cost and the work value of a piece of
information, and show that the former is essentially the length of the string's
best compression by a reversible computation. We generalize the principle by
deriving bounds on the free energy to be invested for --- or gained from, for
that matter --- a general computation. We then revisit the second law of
thermodynamics and compactly rephrase it (assuming the Church/Turing/Deutsch
hypothesis that physical reality can be simulated by a universal Turing
machine): Time evolutions are logically reversible --- "the future fully
remembers the past (but not necessarily vice versa)." We link this view to
previous formulations of the second law, and we argue that it has a particular
feature that suggests its "logico-informational" nature, namely simulation
resilience: If a computation faithfully simulates a physical process violating
the law --- then that very computation procedure violates it as well.
