A parallel system with two job classes is analyzed. Type-1 jobs require one server for their execution and have exponentially distributed service times while type-2 jobs need two servers and have general service times. The model consists of a single queue served by two servers that may work either independently or in parallel. It is assumed that all jobs are rigid and share the servers according to pure space sharing. We provide closed-form expressions, exact as well as approximate, for various performance measures of interest. The approximate formula is found to be extremely accurate for various distributions of the service times of type-2 jobs. Furthermore, the maximal occupancy of the servers as well as the maximal throughput are examined. Finally, numerical results to investigate the impact of each parameter on system performance are conducted.
