Cost is also an important motivation behind clustering, points out Tushar Chandra, manager of the distributed and cluster systems group at Watson. Forming a cluster out of a bunch of commodity processors can be a lot less expensive way to obtain higher performance than building a faster, dedicated processor. The clustering concept grew naturally out of scientific computing. If one processor isn't enough to solve the problem, more might help. For example, certain common scientific calculations can always be divided up into a number of smaller problems whose solutions can then be combined together to give the right answer.
Clusters are also ideal for Web servers.
If your Web server is accessed interactively from everywhere in the world, it has to be up all the time. The Parallel Cluster IBM's SP product line is based squarely on the clustering concept. With the debut of the SP, IBM researchers developed a series of services that would make the cluster look like a single computer to the user and the application. The responses from those nodes then bypass the dispatcher and go back directly to the user. The Network Dispatcher makes it transparent to you.