The IMC structure is shown in Figure 8-12. The distinguishing characteristic of this structure is the process model, which is in parallel with the actual process (plant). Note that (~) is generally used to represent signals associated with the model. Other literature sources may use a subscript (such as m) to represent the model. Figure 8-13 illustrates that both the controller and model exist as computer computations; it is convenient to treat them separately for design and analysis.