集群计算
集群计算(Cluster Computing)在计算机中，集群是使用多个计算机，如典型的个人计算机或UNIX工作站；多个存储设备；冗余互联，来组成一个对用户来说单一的高可用性的系统。集群计算能够被用来实现负载均衡，集群计算的倡导者提出，对一个企业来说，集群在许多情况下，能够达到99.999%的可用性。集群的一个主要思路就是，对外界来说，集群就像是一个唯一的系统。
集群的一个常用用途就是在一个高流量的网站中实现负载均衡。一个网页请求被送到“管理者”服务器，然后此服务器决定此请求由几个相同Web服务器中的哪一个进行处理。这种Web Farm（根据配置有时候被这样称呼）将能够提升通信量和处理速度。
集群最早是在20世纪80年代DEC的VMS系统中出现的，IBM的sysplex是与集群接近的大型主机系统。微软、Sun微系统，以及其它主导硬件和软件流的公司提供有集群包，并保证提供可扩展性和可用性。随着通信量和可用性保证的增加，集群的整个部分或局部零件的大小与数量都可以增加。
集群计算还可以被用来进行低廉的并行计算，这些并行计算通常为科学研究或其它需要并行运算的应用服务。一个著名的例子就是裴欧沃夫（Beowulf）计划，它使用一定数量现成的个人计算机组成集群来实现科学应用。
Cluster computingIn computers, clustering is the use of multiple computers, typically PCs or UNIX workstations, multiple storage devices, and redundant interconnections, to form what appears to users as a single highly available system. Cluster computing can be used for load balancing as well as for high availability. Advocates of clustering suggest that the approach can help an enterprise achieve 99.999 availability in some cases. One of the main ideas of cluster computing is that, to the outside world, the cluster appears to be a single system.
A common use of cluster computing is to load balance traffic on high-traffic Web sites. A Web page request is sent to a "manager" server, which then determines which of several identical or very similar Web servers to forward the request to for handling. Having a Web farm (as such a configuration is sometimes called) allows traffic to be handled more quickly.
Clustering has been available since the 1980s when it was used in DEC's VMSsystems. IBM's sysplex is a cluster approach for a mainframe system. Microsoft, Sun Microsystems, and other leading hardware and software companies offer clustering packages that are said to offer scalability as well as availability. As traffic or availability assurance increases, all or some parts of the cluster can be increased in size or number.
Cluster computing can also be used as a relatively low-cost form of parallel processing for scientific and other applications that lend themselves to parallel operations. An early and well-known example was the Beowulf project in which a number of off-the-shelf PCs were used to form a cluster for scientific applications.