  Landauer's principle states that the erasure of information must be a
dissipative process. In this paper, we carefully analyze the recording and
erasure of information on a physical memory. On the one hand, we show that in
order to record some information, the memory has to be driven out of
equilibrium. On the other hand, we derive a differential version of Landauer's
principle: We link the rate at which entropy is produced at every time of the
erasure process to the rate at which information is erased.
