  We briefly address Landauer's Principle and some related issues in thermal
demons. We show that an error-free Turing computer works in the zero-entropy
limit, which proves Landauer's derivation incorrect. To have a physical logic
gate, memory or information-engine, a few essential components necessary for
the operation of these devices are often neglected, such as various aspects of
control, damping and the fluctuation-dissipation theorem. We also point out
that bit erasure is typically not needed or used for the functioning of
computers or engines (except for secure erasure).
