  At one extreme, von Neumann argued that any logical operation necessarily generated a minimum quantity of heat. Gabor and Brillouin had argued that measurement, at least, generated heat. Landauer and Bennett argued that only logically irreversible operations need generate heat, but that measurement is logically reversible. This was backed up by the presentation of physical processes that could, in principle, perform a measurement with arbitrarily little heat generation. Bennett argued that while the measurement processes discussed by Gabor and Brillouin, using scattered light, generate heat, they were incorrect to generalise this to the claim that all measurement process must necessarily do the same. However, a similar charge may be levelled at Landauer's principle. Although explicit models for resetting operations have been constructed that get arbitrarily close to a minimum heat generation of k T ln 2, what is needed is a proof that no physical process can do better. A literature now exists examining the strength of this claim, and in particular what are the physical and statistical assumptions underpinning their arguments.