  It is generally accepted, following Landauer and Bennett, that the process of
measurement involves no minimum entropy cost, but the erasure of information in
resetting the memory register of a computer to zero requires dissipating heat
into the environment. This thesis has been challenged recently in a two-part
article by Earman and Norton. I review some relevant observations in the
thermodynamics of computation and argue that Earman and Norton are mistaken:
there is in principle no entropy cost to the acquisition of information, but
the destruction of information does involve an irreducible entropy cost.
