Clustering technologies allow servers to be connected into multiple-server units called server clusters. Each computer connected in a server cluster is referred to as a node. Nodes work together, acting as a single unit, to provide high availability for business applications and other critical resources, such as Microsoft Internet Information Services (IIS), Microsoft SQL Server, or Microsoft Exchange Server. Clustering allows administrators to manage the cluster nodes as a single system rather than as individual systems. Clustering allows users to access cluster resources as a single system as well. In most cases, the user doesn’t even know the resources are clustered.