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f云计算动态供应硬件、软件和数据集，以此方式按需应用一个拥有弹性资源的虚拟化平台。其目的是通过在数据中心使用服务器集群和巨型数据库而将桌面计算转移到一个面向服务的平台。云计算充分利用其低成本与简单的特性既惠及用户也惠及提供商。机器虚拟化使这样的成本效益成为可能。云计算意在同时满足许多用户应用程序的需要。云生态系统必须设计得具有安全性、可信性和可靠性。有些计算机用户将云视为一个集中式资源池，而另外一些计算机用户则认为云是一个在所用的各个服务器实行分布式计算的服务器集群。传统上，一个分布式计算系统往往由一个自主管理域（如一个研究实验室或公司）为内部计算需要而拥有和使用。然而，这些传统系统遭遇数个性能瓶颈：系统维护需要不断进行；利用率差；与硬件／软件升级有关的费用日益增长。作为一种按需计算范式，云计算可解决这些问题或可使我们摆脱这些问题。
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