Inexpensive dual and quad CPU SMP (Symmetric Multi Processing) systems are now widely available. However, systems with more than four SMP processors are expensive because memory bus contention between the processors becomes more of a problem as the number of processors sharing the memory bus increases. Clustering several independent systems is one way of avoiding this memory contention. However, the memory bandwidth of e.g. AMD Hypertransport in AMD64 SMP systems is orders of magnitude greater than COTS (Commodity Off The Shelf) hardware such as Gbit Ethernet. Despite this limitation, useful Beowulf clusters can be built using COTS hardware. The easy-ubuntu-clustering blueprint is an effort to bring 'easy' clustering support directly into Ubuntu. The community documentation about Ubuntu Clustering is an attempt to gather together information about Ubuntu clustering that is dispersed over different threads in the Ubuntu Forums. Please post links to existing Ubuntu clusters here, and also links to information about clustering relevant to Ubuntu users.