The simulators implement various models of computation. Most of these models of computation can be viewed as a framework for component-based design, where the framework defines the interaction mechanism between the components.A Model of Computation gives an interaction mechanism for components to deal with concurrency and time. The utility of a model of computation stems from the modeling properties that apply to all similar models. For many models of computation these properties are derived through formal mathematics. Depending on the model of computation, the model may be deterministic, statically schedulable, or time safe. Because of its modeling properties, a model of computation represents a style of modeling that is useful in any circumstance where those properties are desirable. In other words, models of computation form design patterns of component interaction, in the same sense that Gamma and others. describe design patterns in object oriented languages.
For a particular application, an appropriate model of computation does not impose unnecessary constraints, and at the same time is constrained enough to result in useful derived properties.

VisualSim consists of five major simulators

• Digital
  The simulator maintains a Calendar Queue with sequences of events on a time line.
  
• Digital Untimed
  The execution is statistical and determined prior to execution.
  
• Continuous Time
  Simulator finds a fixed-point, i.e., a set of continuous-time functions that satisfy all the relations.
  
• SystemC
  Embedded systems frequently contain components that are best modeled using differential equations
  
• Finite State Machine
  Case statement in a graphical form defining sequential control logic.

Sysml
The Systems Modelling Language (SysML) is a general purpose modeling language.