Modern computers combine the capacity not only to carry out calculations very quickly but also to make many calculations simultaneously, to remember what they have done, as well as their instructions, and to do all this using very little space and with great reliability. These abilities to calculate, record and remember far exceed those of people and, where these qualities are all that are required, computers can substitute for people — very often for many people. But, of course, agriculture as a whole does not employ many people and the scope for substitution may not be great: it is, however, likely to be greater in animal rather than in crop production.

Computers can only make decisions where adequate data are available (Blackie and Dent, 1979) and where the weight to be attached to each piece of information is pre-determined. The conceptual framework also has to be adequate, so that decisions are also pre-determined for given values of the variables considered. This is not the same thing as exercising judgement but, in fact, it can come very close to it. A computer landing an aircraft, playing chess or diagnosing a disease behaves very like a human being, and a very skilful, experienced one at that. Computers have considerable advantages in terms of speed of response to feedback and thus, in addition to the power of decision, they possess great power to control and monitor operations.

In looking to the future, therefore, it is probably not necessary to try and predict what computers will be able to do: they are already able to do most things and will be able to do virtually anything. It does not follow, of course, that they should be used just because it is technically possible: mere technical feasibility is not sufficient justification for doing anything. This is true of all technical developments and computers are no different in two important respects.