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.