  The association of information with entropy has been argued on plausibility
arguments involving the operation of imaginary engines and beings, and it is
not a universal theorem. In this paper, a theorem by Charles Bennett on
reversible computation is recognized as the much needed theorem. It is proposed
a real, non thermal engine, operated by humans. Its operation has stages
analogous to the stages in Bennett's reversible three-tape computer. The engine
makes possible to prove two results: (1) the engine operates on two laws,
similar to the laws of thermodynamics, which are conditions on the possibility
of resetting the engine; (2) entropy is the measure of erased information, and
is measured in physical units, which complies with Landauer's principle. A
prototype at work is shown in video.
