Circuits in which all outputs at any given time depend only on the inputs at that time are called combinational logic circuits.
A combinational circuit performs a specific information-processing operation fully specified logically by a set of Boolean functions. Sequential circuits employ memory elements (binary cells) in addition to logic gates.
Their outputs are a function of the inputs and the state of the memory elements. The state of memory elements, in turn, is a function of previous inputs. As a consequence, the outputs of a sequential circuit depend not only on present inputs, but also on past inputs, and the circuit behavior must be specified by a time sequence of inputs and