  I give a quick overview of some of the theoretical background necessary for
using modern non-equilibrium statistical physics to investigate the
thermodynamics of computation. I first present some of the necessary concepts
from information theory, and then introduce some of the most important types of
computational machine considered in computer science theory.
  After this I present a central result from modern non-equilibrium statistical
physics: an exact expression for the entropy flow out of a system undergoing a
given dynamics with a given initial distribution over states. This central
expression is crucial for analyzing how the total entropy flow out of a
computer depends on its global structure, since that global structure
determines the initial distributions into all of the computer's subsystems, and
therefore (via the central expression) the entropy flows generated by all of
those subsystems. I illustrate these results by analyzing some of the
subtleties concerning the benefits that are sometimes claimed for implementing
an irreversible computation with a reversible circuit constructed out of
Fredkin gates.
