 photons, the photon energy would have to supersede that of the ambient electromagnetic radiation, thus bringing a quantum of heat kB T into the system. To move the trapdoor, the "demon" must also be material. Thus, some form of heat transfer should occur during the process, resulting in the heating of both the demon and the gas, canceling the cooling Reversible computation effect of molecule separation. In 1963, R. Feymann observed that the demon would not be able to get rid of the heat gained in his molecule measurements, ending up in "shaking into Brownian motion" with the inability to perform the task! Most of the above conjectures, along with the multiplication of improved "demon engines," contributed to turn Maxwell's initial paradox into an ever-deepening enigma. This is how the concept of information entropy came into the picture. Szilárd considered a demon engine processing just a single gas molecule. If the demon knew where the molecule was located, then he could move a frictionless piston to confine it where it belonged, without any work expenditure! Then the pressure effect of the molecule on the piston could be used to generate work, such as lifting a weight. The intuitive, yet not consolidated idea, was that the entropy bookkeeping could be balanced should some positive entropy be associated with the information concerning molecules or the demon's memory itself. Either the demon keeps track of any of its binary decisions (open trapdoor to molecule coming from A or B) or it erases them. In the first case, the demon's memory space expands, which goes together with an entropy increase (number of accessible memory states in the demon's mind). At some point, however, the memory space is exhausted, and information must be erased. In the second case, the memory is cleared one bit at a time prior to the next binary decision. Whether the memory is cleared at once or bit after bit after each demon operation, the action of erasure is irreversible. According to thermodynamics, irreversible processes generate po