Abstract: A simulation system, a computer product to implement a simulation method, and a method of simulating a digital circuit that has at least one element and at least one clock signal having clock attributes. The method includes maintaining a data structure for time-scheduled events scheduled to occur at particular simulation-times; and maintaining a data structure for clock-scheduled events each corresponding to a particular clock signal and scheduled to occur at a time that can be determined from at least one attribute of the clock signal, such that clocked-scheduled events are distinguishable from time-scheduled events, and such that each and every transition of any clock signal need not be scheduled in the time-scheduled event data structure.