云计算

what is cloud computing?
Cloud computing is a way of using I.T.that has these five equally important traits.
First, you get computing resources on-demand and self-service. All you have to do is use a simple interface and you get the processing power, storage, and network you need, with no need for human intervention.
Second, you access these resources over the net from anywhere you want.
Third, the provider of those resources has a big pool of them and allocates them to customers out of that pool. That allows the provider to get economies of scale by buying in bulk and pass the savings on to the customers. Customers don’t have to know or care about the exact physical location of those resources.
Fourth, the resources are elastic. If you need more resources you can get more, rapidly. If you need less, you can scale back.
And last, the customers pay only for what they use or reserve as they go.
If they stop using resources, they stop paying.

云计算通过互联网按需提供IT 资源，并且采用按使用量付费的定价方式。
可以从任何地方通过网络访问计算/存储等资源。
资源具有弹性，灵活的扩容缩容方式。
虚拟化技术实现，用户不需要关注硬件。
包含分布式计算、数据备份和数据存储、可扩展性、虚拟化，弹性等。
云计算一般分为三类：基础架构即服务（IaaS）、平台即服务（PaaP）和软件即服务（SaaS）