In the 1980s it was believed computer performance was best improved by creating faster and more ecient processors. This idea was challenged by parallel processing, which in essence means linking together two or more computers to jointly solvea computational problem. Since the early 1990s there has been an increasing trend to moveaway from expensive and specialized proprietary parallel supercomputers (vector-supercomputers and massively parallel processors) towards networks of com-puters (PCs/Workstations/SMPs). Among the driving forces that have enabled this transition has been the rapid improvementin the availabilityofcommodity high-performance components for PCs/workstations and networks. These technologies are making a network/cluster of computers an appealing vehicle for cost-eective parallel processing and this is consequently leading to low-cost commodity super-computing.