English: N-atom vacuum-pump memory: A symmetric bi-partitioned cell for the isothermal compression of an N-atom ideal gas into either its left or right half, perhaps first discussed by Leó Szilárd, which serves as a physical system about whose state mutual information is available for a well-defined price in free energy. If one is further provided with some mechanism (e.g. spectroscopic) for reading its state in the one-atom case, it may also serve as an efficient mechanically-operated single-bit memory. The "setting" process involves removing the barrier between compartments, using the piston on one side to relocate all atoms into the opposite half and then returning the barrier before returning the piston to its original position. The required work is W = NkT ln[2]. It's reset status may be defined as true if we know that the atoms are located in the right half of the container, and false if we don't know this to be the case.