Event simulation typically traces every signal transition and continues this until stable state is reached. Simulation based on events in logic, which means, whenever there is change in a input event, the output is evaluated. Means both timing and functional information is available. With this glitches in signal changes can be observed. Event based simulators are slow when compared with cycle based simulators.
Cycle Based Simulation
Cycles based simulator takes the advantage of the fact that most digital circuits are synchronous in nature. Cycle simulation typically re-evaluates the state of the circuit as a whole, once upon each external trigger, usually without evaluating any intermediate node states. Cycle based simulator is very fast compared to event based simulator. Disadvantage of cycle based simulator are it cannot detect glitches and setup and hold checks cannot be done. In cycle based simulators, delays cannot be specified.