There is little to say here. One can link several workstations together, either by ethernet (cheap) or by switches (more expensive), and run message passing to transfer data among the processor units. In principle, as many workstations as desired can be clustered. Complications arise when different processors are joined. The speed of each processor, as well as memory and work assignment, can lead to wrokload imbalance among the processors. The programmer must take into account load and code in such a way that all processors have profitable work to perform.