Machines and Societies 
SELF-REGULATING INFORMATION SYSTEMS 
The three examples just mentioned are all of self-regulating 
information systems. Self-regulation of a passive sort can of 
course be achieved without information flow. A railway train, 
for example, needs no steering gear, for its course is passively 
regulated by the reaction of the rails. A ship, by contrast, must 
be actively steered according to information on its deviations 
from true course. To make this kind of process self-regulating 
(as in an automatic pilot) we require three features: 
(a) Control (in this case, by the helm) whereby the form of 
action can be selected from a range or repertoire, without 
supplying all the energy required (most of which in this case 
comes from the engines). 
(b) Indication (for example by a compass) of the deviation or 
mismatch between the present state of affairs and some defined 
goal state. 
(c) Calculation of the form of controlling action which will 
most effectively reduce the mismatch. 
In the simplest cases the third function may be performed 
by a direct link between indicator and control, so connected 
that an increase in the indication of mismatch leads to a 
reduction in the activity giving rise to it—an arrangement 
known as negative feedback. If the link were connected the 
wrong way round, so that an increase in mismatch led to an 
increase in the activity responsible, the feedback would be 
termed positive. Such a system would automatically drive 
itself so far as possible away from the goal state, becoming a 
goal-shunning rather than a goal-seeking system. 
Unfortunately it is all too easy for a theoretically self- 
regulating system to become unstable, continually over- 
correcting itself in a growing series of wild swings in opposite 
directions. Sluggishness of response is the most common enemy, 
causing the corrective control to get out of step with the mis- 
match that it should reduce, so that oscillations are built up 
instead of being damped down. (A rough-and-ready illustration 
is provided by a child’s swing, which is kept oscillating by 
suitable timing of thrusts towards its position of equilibrium. 
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