Clustering

In a computer system, a cluster is a group of servers and other resources that act like a single system and enable high availability and, in some cases, load balancing and parallel processing.
Uses:
Cluster computing can be used for load balancing as well as for high avilability. A common use of cluster computing is to load balance traffic, on high-traffic Web site. Windows Server clusters provide failover support for back-end applications and services that require high availability and data integrity. These back-end applications include enterprise applications such as database, file server, enterprise resource planning (ERP), and messaging systems.

Features:
First designed for the Microsoft Windows NT® Server 4.0 operating system, server clusters are substantially enhanced in the Microsoft Windows Server 2003, Enterprise Edition, and Windows Server 2003, Datacenter Edition, operating systems. With server clusters you can connect multiple servers together in order to provide high availability and easy manageability of data and programs running within the cluster. Server clusters provide the following three principal advantages in clustering technology

• Improved availability by enabling services and applications in the server cluster to continue providing service during hardware or software component failure or during planned maintenance.
  Increased scalability by supporting servers that can be expanded with the addition of multiple processors (up to a maximum of eight processors in Windows Server 2003, Enterprise Edition, and 32 processors in Windows Server 2003, Datacenter Edition), and additional memory (up to a maximum of 8 gigabytes [GB] of random access memory [RAM] in Enterprise Edition and 64 GB in Windows Server 2003 Datacenter Edition).·
• Improved manageability by enabling administrators to manage devices and resources within the entire cluster as if they were managing a single computer

The cluster service is one of two complementary Windows clustering technologies provided as extensions to the base Windows Server 2003 and Windows 2000 operating systems. The other clustering technology, Network Load Balancing (NLB), complements server clusters by supporting highly available and scalable clusters for front-end applications and services such as Internet or intranet sites, Web–based applications, media streaming, and Microsoft Terminal Services.

There is an important to be noted that Sharepoint and Exchange doesnot support Clustering