As Beowulf-style clusters have proliferated, many computational scientists have discovered that, although clusters provide adequate CPU performance for most applications, more finely-grained models are often limited by the performance of the network that interconnects nodes. While the network is typically Fast Ethernet (100 Mb/s) or Gigabit Ethernet (1.0 Gb/s), it's still not fast enough to run applications originally developed for shared memory parallel systems or commercial memory systems featuring high performance, custom-designed switched interconnects.

Such applications have stimulated the market for scalable networks that provide high bandwidth and low latency on commodity clusters. (Bandwidth is the throughput rate of a data channel, while latency is the time it takes to open the channel and initiate the data transfer.) These custom networks -- often adding 50% or more to the per-node cost of Linux clusters -- are not commodity items, and some people claim that, as a result, a cluster sporting one of these sexy networks can not be called a Beowulf. Religious arguments aside, many researchers consider these high performance interconnects a necessity for their computational clusters.

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