A computer can indeed be a metaphor for man, then it becomes relevant to discover whether man is all bits on the inside. But an alternative to metaphor is at hand. An abstract concept of an information processing system has emerged with the development of the digital computer. In fact, a whole array of different abstract concepts has developed, as scientists have sought to capture the essence of the new technology in different ways. The various features that make the digital computer seem machinelike—its fast arithmetic, its simply ordered memory, its construction by means of binary elements—all have faded in the search for the essential.