Input Variable And Output variable Input Variable This variable shows the effect of the surroundings on the process. It normally refers to those factors that influence the process. An example of this would be the flow rate of the steam through a heat exchanger that would change the amount of energy put into the process. There are effects of the surrounding that are controllable and some that are not. These are broken down into two types of inputs. Manipulated inputs Disturbances Manipulated inputs:- variable in the surroundings can be control by an operator or the control system in place.  Disturbances:- inputs that can not be controlled by an operator or control system. There exist both measurable and immeasurable disturbances. Output variable SISO MIMO Single input-Single Output (SISO):- for one control(output) variable there exist one manipulate (input) variable that is used to affect the process  Multiple input-multiple output(MIMO):- There are several control (output) variable