There has been much discussion for decades over the proper concepts of minimum dissipation per logic gate and what is required for computation, as well as early arguments over logically reversible machines. Here these arguments, and the thermodynamics related to them, are discussed in terms of what is required for a computing machine. This gives a set of requirements for a valid computer that arise already from Turing and a set of limitations on energy dissipation and entropy. How these requirements, and new ones, affect quantum computation is also discussed.