  With the ferromagnet representing the demon's memory, Bennett had given an explicit counter-example to the arguments of Szilard and Brillouin, that measurement is necessarily dissipative. At the same time he argued that the process of resetting the demon's memory is a necessarily logically irreversible step, which incurs the heat generation cost identified by Landauer, and this cost saves a modified form of the second law. Although Bennett gave a particular model for resetting the demons memory, no direct proof was given that there can be no better way. Unlike Penrose's argument, Landauer's principle seems to be assumed, rather than derived.