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A control system which monitors its effect onthe system it is controlling and modifies its outputaccordingly. For example, a thermostat has two inputs: thedesired temperature and the current temperature (the latter isthe feedback). The output of the thermostat changes so as totry to equalise the two inputs.Computer disk drives use feedback control to position theread/write heads accurately on a recording track. Complexsystems such as the human body contain many feedback systemsthat interact with each other; the homeostasis mechanisms thatcontrol body temperature and acidity are good examples.