See you later, simulator

Simulation (or modeling) programs mimic a physical process; the process being simulated can be treated as discreet (occurring at points in time) or continuous (always occurring).

Simulation programs are similar to process control programs, except that they have two "clocks":  a simulation clock which records the time expired in the simulated process and a real-time clock which records the time taken by the program in the real world.

Tasks in a discrete simulation are broken up into events such as the beginning of an operation or the end of an operation.  In a continuous simulation, tasks are broken up into small moments, in which all operations that are active perform one cycle of their actions.

Tasks in a simulation usually don't use the process that they are simulating, so there is less dependency on the details of the process's operation.

The simulation clock need not advance in proportion to real time, and in discreet simulations may advance over intervals in which no events occur.  Tasks are usually not time-constrained, as they would be in a process monitoring or control system.

The routine that dispatches tasks (determines which task to run next) in a simulation program usually gathers statistics about the simulation times the task is ready or blocked and the condition that blocks the task; it also handles sequentialization (insuring that resources are used by one task at a time) within the simulation, and controls the simulation clock.