Electronic computers are intended to carry out any definite rule of thumb process which could have been done by a human operator working in a disciplined but unintelligent manner. The electronic computer should however obtain its results very much more quickly. The human computer with whom we are comparing it may be imagined as supplied with various computing aids. He should have a desk machine, paper to write his results on, and more paper on which is written a detailed account of how the calculation is to be carried out. These aids have their analogues in the electronic computer. The desk machine is transformed into the computing circuits, and the paper becomes the ``information store'' or more briefly the ``store'', whether it is paper used for results or paper carrying instructions. There is also a part of the machine called the control which corresponds to the computer himself. If his possible behaviour were very accurately represented this would have to be a formidable complicated circuit. However we really only require him to be able to obey the written instructions and these can be made so explicit that the control can be quite simple. There remain two more components of the electronic computer. These are the input and output mechanisms, by which information is to be transformed from outside into the store or conversely. If the analogy of the human computer is to be maintained these parts would correspond to his ears and voice, by means of which he communicates with his employer.