What is clustering? What are the different algorithms used for

Question :What is clustering? What are the different algorithms used for
clustering? (EJB)
Answer :Clustering is grouping machines together to transparantly provide
enterprise services.The client does not now the difference between
approaching one server or approaching a cluster of servers.Clusters
provide two benefits: scalability and high availability. Further information
can be found in the JavaWorld article J2EE Clustering.