A parallel system with two machines is shown in Fig. 6. A single queue serves both machines. When a machine completes a part, a new part moves from the queue, if it is not empty, to the machine. If the queue is empty when a machine completes its operation, the machine remains idle until another unit arrives. Both machines in Fig. 6 are shown with the same service rate, but the machines may have different parameters.

Figure 6. A Two-Machine Parallel System

The Extend model for the two parallel machine case is shown in Figure. 7.

The block at the far right is a Plotter block that collects statistics on the number of parts leaving each station and the number in the queue. The output of the plotter for a 250-minute run is shown in Figure 8.