The increase in network and processing capacity for commodity platforms has enabled Networks of Workstations to become affordable alternatives to dedicated parallel computers. However layered communication protocols used on commodity Operating Systems (such as TCP/IP) were not originally designed for use in high performance cluster computing, so they give rise to communication bottlenecks due to interrupt generation overheads, in-memory copying, protocol processing, as well as latencies induced by inefficient use of buses and IO devices. In this book we identify such bottlenecks...