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A computer cluster consists of a set of loosely or tightly connected computers that work together so that, in many respects, they can be viewed as a single system. Unlike grid computers, computer clusters have each node set to perform the same task, controlled and scheduled by software.〔(Grid vs cluster computing )〕 The components of a cluster are usually connected to each other through fast local area networks ("LAN"), with each ''node'' (computer used as a server) running its own instance of an operating system. In most circumstances, all of the nodes use the same hardware〔(Cluster vs grid computing )〕 and the same operating system, although in some setups (i.e. using Open Source Cluster Application Resources (OSCAR)), different operating systems can be used on each computer, and/or different hardware.〔(Hardware of computer clusters not always needing to be the same, probably depends on software used )〕 They are usually deployed to improve performance and availability over that of a single computer, while typically being much more cost-effective than single computers of comparable speed or availability. Computer clusters emerged as a result of convergence of a number of computing trends including the availability of low-cost microprocessors, high speed networks, and software for high-performance distributed computing. They have a wide range of applicability and deployment, ranging from small business clusters with a handful of nodes to some of the fastest supercomputers in the world such as IBM's Sequoia. The applications that can be done however, are nonetheless limited, since the software needs to be purpose-built per task. It is hence not possible to use computer clusters for casual computing tasks.〔(Grid and cluster computing, limitations )〕 ==Basic concepts== The desire to get more computing power and better reliability by orchestrating a number of low-cost commercial off-the-shelf computers has given rise to a variety of architectures and configurations. The computer clustering approach usually (but not always) connects a number of readily available computing nodes (e.g. personal computers used as servers) via a fast local area network.〔''Network-Based Information Systems: First International Conference, NBIS 2007'' ISBN 3-540-74572-6 page 375〕 The activities of the computing nodes are orchestrated by "clustering middleware", a software layer that sits atop the nodes and allows the users to treat the cluster as by and large one cohesive computing unit, e.g. via a single system image concept.〔 Computer clustering relies on a centralized management approach which makes the nodes available as orchestrated shared servers. It is distinct from other approaches such as peer to peer or grid computing which also use many nodes, but with a far more distributed nature.〔 A computer cluster may be a simple two-node system which just connects two personal computers, or may be a very fast supercomputer. A basic approach to building a cluster is that of a Beowulf cluster which may be built with a few personal computers to produce a cost-effective alternative to traditional high performance computing. An early project that showed the viability of the concept was the 133-node Stone Soupercomputer. The developers used Linux, the Parallel Virtual Machine toolkit and the Message Passing Interface library to achieve high performance at a relatively low cost. Although a cluster may consist of just a few personal computers connected by a simple network, the cluster architecture may also be used to achieve very high levels of performance. The TOP500 organization's semiannual list of the 500 fastest supercomputers often includes many clusters, e.g. the world's fastest machine in 2011 was the K computer which has a distributed memory, cluster architecture.〔(TOP500 list ) To view all clusters on the TOP500 select "cluster" as architecture from the sublist menu.〕〔M. Yokokawa et al ''The K Computer'', in "International Symposium on Low Power Electronics and Design" (ISLPED) 1-3 Aug. 2011, pages 371-372〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Computer cluster」の詳細全文を読む スポンサード リンク
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