A comparison of sequential and iterative circuits

Traditionally, the major effort of switching theory has been devoted to finding techniques for synthesizing optimum circuits. An optimum circuit is generally understood to be one which exhibits the required relationship among its input and output signals, and also costs less to construct than any other such circuit. The requirements on the relation among input and output signals can include not only a specification of which output signals are to result from the various combinations or sequences of input signals, but also a restriction on the delay between the application of the input and the appearance of the corresponding output signal. The desired synthesis procedure is one which does not place any restrictions on the form of the resulting network. Thus, the final circuit is to be optimum for the entire class of circuits which satisfy the design specifications. Even this is not exactly what is desired since a circuit which requires very complicated interconnections would probably be undesirable because of difficulties involved in maintaining proper operation. To be completely accurate, the cost of the circuit should include some measure of the circuit complexity.