The simplest distributed system model is a multiprocessor system where the system consists of a number of processes that can run on several separate processors. This model is generally used in large real-time systems.
The use of multiple processors is useful for improving system performance and flexibility. The distribution of processes to processors can be predetermined or can be controlled by a dispatcher who decides which processes will be allocated to each processor. An example of this type of system can be seen in Figure 10.1, which is an example of a traffic control system model. A set of distributed sensors collects information from the traffic flow and processes the information locally before sending it to the control room. The operator makes decisions using this information and gives instructions to the different traffic light control processes. There are separate logical processes to handle the control room sensors and the traffic lights, while these processes run on separate processors.
Figure 10.1 Traffic Control Model
A software system consisting of multiple processes does not have to be a distributed system. Indeed, if more than one processor is available, distribution can be implemented.