云计算的定义

Cloud computing is a general term for anything that involves delivering hosted services over the Internet. These services are broadly divided into three categories: Infrastructure-as-a-Service (IaaS), Platform-as-a-Service (PaaS) and Software-as-a-Service (SaaS). The name cloud computing was inspired by the cloud symbol that's often used to represent the Internet in flowcharts and diagrams.

云计算是一个对任何涉及用互联网提供托管服务的泛称。这些服务大体上分为三类：基础设施即服务(IaaS)、平台即服务(PaaS)和软件即服务(SaaS)。云计算这个名字的灵感来自于通常用流程图和图表来表示互联网的云符号。

A cloud service has three distinct characteristics that differentiate it from traditional hosting. It is sold on demand, typically by the minute or the hour; it is elastic -- a user can have as much or as little of a service as they want at any given time; and the service is fully managed by the provider (the consumer needs nothing but a personal computer and Internet access). Significant innovations in virtualization and distributed computing, as well as improved access to high-speed Internet and a weak economy, have accelerated interest in cloud computing.

云服务有三个明显的特点使它区别于传统托管。它根据顾客的要求来进行销售——按小时收费或者按分钟收费;它是具有弹性的——用户可以在任何给定的时间内享受他们需要的或多或少的服务；并且这个服务完全是由提供者管理的(消费者除了需要个人电脑和可访问的互联网，其他的都不需要。在虚拟化和分布式计算上的重大创新,以及改进了的对高速互联网的访问和疲软的经济,已经提高了云计算的利润。

A cloud can be private or public. A public cloud sells services to anyone on the Internet. (Currently, Amazon Web Services is the largest public cloud provider.) A private cloud is a proprietary network or a data center that supplies hosted services to a limited number of people. When a service provider uses public cloud resources to create their private cloud, the result is called a virtual private cloud. Private or public, the goal of cloud computing is to provide easy, scalable access to computing resources and IT services.

云可以是私有云或者公有云。其中，公有云通过网络面向所有人来售卖其服务。（目前，亚马逊网络服务是最大的公有云提供商。）私有云对于有限数量的人来说是一个专有网络或者提供主机服务的数据中心。当一个服务提供商用公众云资源来创造他们的私有云时，这个云就被称作是虚拟私有云。不管是私有云还是公有云，云计算的目的是为了提供简单的、可延伸的访问计算机资源和IT服务的通道。

Infrastructure-as-a-Service like Amazon Web Services provides virtual server instance API to start, stop, access and configure their virtual servers and storage. In the enterprise, cloud computing allows a company to pay for only as much capacity as is needed, and bring more online as soon as required. Because this pay-for-what-you-use model resembles the way electricity, fuel and water are consumed, it's sometimes referred to as utility computing.

即像亚马逊网络服务提供虚拟服务器实例API来启动、停止、访问和配置虚拟服务器和存储。在企业中,如果有必要，云计算允许一个公司只需要提供尽可能多的技术支持，而且只要求带来更多的网上便利。因为这个支付你使用模型类似于电力、燃料和水的消耗,所以它有时被称为实用计算。

Platform-as-a-service in the cloud is defined as a set of software and product development tools hosted on the provider's infrastructure. Developers create applications on the provider's platform over the Internet. PaaS providers may use APIs, website portals or gateway software installed on the customer's computer. Force.com, (an outgrowth of Salesforce.com) and Google Apps are examples of PaaS. Developers need to know that currently, there are not standards for interoperability or data portability in the cloud. Some providers will not allow software created by their customers to be moved off the provider's platform.

云中的平台即服务（Platform-as-a-service）被定义为基于提供商基础设施上的一组软件及产品开发工具。开发人员通过互联网在供应商的平台上创建应用程序。PaaS（平台即服务）提供商可以使用安装于客户端电脑上的APIs，网站门户或网关软件等资源。Force.com网站(Salesforce.com网站的一个分枝)和谷歌应用套件是PaaS应用的两个例子。开发人员需要知道当前的这种现状，即云中还没有明确互用性和数据迁移的标准。一些供应商将不允许那些顾客在脱离供应商平台情形下自己研发软件。

In the software-as-a-service cloud model, the vendor supplies the hardware infrastructure, the software product and interacts with the user through a front-end portal. SaaS is a very broad market. Services can be anything from Web-based email to inventory control and database processing. Because the service provider hosts both the application and the data, the end user is free to use the service from anywhere.

在软件即服务（software-as-a-service）的云模式中，供应商通过前端门户提供了硬件基础设施、软件产品，并且还可以与用户进行互动。SaaS（软件即服务）是一个非常广阔的市场。服务可以是任何基于网络的电子邮件，这些邮件可以联系到库存控制和数据库处理系统。由于服务提供商掌管应用程序和数据，所以最终用户可以在任何地方免费使用服务。