1. Overview of cloud computing
Cloud Computing (Cloud Computing) is based on the Internet related services, use and interactive mode, usually involves using the Internet to provide dynamic easy extension and often virtualized resources,

2. The main service in cloud computing
Cloud computing is still in its infancy, there is a vast amount of all kinds of companies in the development of different cloud computing services, cloud computing has various forms, simple cloud computing can be seen everywhere in People's Daily online applications, such as tencent QQ space to provide the online production of Flash images, Google's search service, GoogleDoc, GoogleApps etc., at present, cloud computing services main forms are: SaaS (SoftwareasaService), PaaS (PlatformasaService), IaaS (InfrastructureasaService),
(1) software as a service (SaaS)
SaaS service provider will be unified arrangements on your own server applications, users according to the demand order from vendor application software services via the Internet, the number of service providers according to the customer of the software, the length of time factors such as the charge, and provide customers with the software model, via a browser is the advantage of this service mode, by the service provider of maintenance and management software, the hardware facilities, offers software running can have access to the Internet terminals, users only need to use software anytime and anywhere, this mode, the customer is no longer like the traditional model to spend a lot of money on hardware, software, maintenance personnel, need only spending a certain amount of rental services, through the Internet can enjoy the corresponding hardware, software and maintenance services, this is the network application of the most effective business model, for small businesses, SaaS is the best way to adopt advanced technology,
In enterprise management software, SaaS model of cloud ERP can let customers according to the number of concurrent users, the functions, data storage capacity, using a combination of different length according to need to pay the service fee, neither software license fee, also do not need to pay the cost of purchasing servers and other hardware equipment, also do not need to pay for the operating system, database platform software such as cost, also need not bear the custom software project, development, implementation, also do not need to pay for IT maintenance department spending, cloud ERP is actually inherited open source ERP from licensing fees only the most important characteristics of service fee, is highlights the ERP of the service product,
(2) the platform as a service (PaaS)
The development environment as a service to provide, this is a kind of distributed service platform, vendor development environment, server platforms, hardware resources and other services to clients, users on the basis of its platform customization to develop their own application and passed to other customers through its server and the Internet, the PaaS can provide enterprise or individual research and development of middleware platform, application development, database, application server, test, hosting and application services,
(3) infrastructure service (IaaS)
IaaS is the vendor's "cloud" composed of multiple servers infrastructure, as the meter service provided to clients, it will be the memory, I/O devices, storage and computing power into a virtual resource pool for the industry to provide the required storage resources and virtualization of servers and other services, this is a way of hosting type hardware, users pay to use the manufacturer's hardware facilities,

3. The classification of cloud computing
Cloud computing by type is divided into: public cloud, the cloud industry, private cloud, a hybrid cloud, among them, the telecom enterprises to provide all cloud services, private cloud is cloud deployment in their data center, only for their own use, a hybrid cloud can be mixed public and private cloud, also can be mixed industry and private cloud, mainly to security concerns, all Internet data to customer is not important, non-core, not classified business in public cloud/industry cloud, classified the important core business on a private cloud,

4. The key technology of cloud computing

4.1 architecture: the architecture of it probably is divided into three levels: the core service layer, service management, user access interface layer,
Core services layer: (1) is divided into three sub layers (Iaas, Paas, Saas)
(2) service management
(3) the user to access the interface layer (provide users with software)

4.2 data store
4.3 calculation model (distributed programming thought)
4.4 resource scheduling, including heterogeneous resources management, reasonable resource scheduling and allocation, so that the performance is the best, fastest to complete the task,
4.5 virtualization: in order to achieve the maximization of resource utilization and flexibility, the hardware and software support,
Virtualization technology features:
(1) resource sharing
(2) resource custom
(3) the fine-grained resource management