This work is a part of an effort to analyze the physical limitations of computers due to the laws of physics. For example, Bennett1 has made a careful study of the free energy dissipation that must accompany computation. He found it to be virtually zero. He suggested to me the question of the limitations due to quantum mechanics and the uncertainty principle. I have found that, aside from the obvious limitation to size if the working parts are to be made of atoms, there is no fundamental limit from these sources either.
by Richard P. Feynman