Infrastructure as a service; This service type is located at the bottom of cloud service and provides basic computing and storage capabilities. Cloud computing providers have tens of thousands of servers, and users can "rent" these servers through the Internet to meet their IT needs. This service type provides users with IT resources like tap water. In this way, IT can meet the needs of non-IT enterprises for IT resources, without spending a lot of money to buy servers and hire more IT personnel, so that they can concentrate on their main business. At the same time, this cloud service also uses automation technology to automatically allocate an appropriate number of servers according to the user's business volume. Users don't have to consider whether IT resources are suitable for the expansion or contraction of their business, and they don't have to worry about the depreciation of IT facilities. They just need to pay the monthly rent according to their own server usage. Platform as a service; Platform-as-a-service is located in the middle layer of cloud computing, which is mainly aimed at software developers or software developers, and provides an Internet-based software development and testing platform. Software developers can write their own applications directly in the cloud through web-based technology, and they can also host their own applications on this platform. For example, google's App Engine is an extensible web application development and hosting platform. Developers can develop their own web applications and publish them on the platform, so that developers don't have to worry about whether their servers can withstand unknown traffic. This platform is undoubtedly favored by some small start-ups. In addition, such a cloud platform also provides a large number of APIs or middleware for program developers to use, which greatly shortens the program development cycle, and at the same time, the program code stored in the cloud can also be jointly developed conveniently. Most importantly, users don't have to worry about how much hardware support their published applications need, because the cloud can satisfy everything. Software as a service; I believe that software as a service will be familiar to everyone. Almost a lot of software has a web version, such as our common Fetion or QQ. Through the web, we can use the corresponding services without downloading the corresponding software, and we don't have to worry about the update and maintenance of the software. Perhaps for a small software like QQ, we can't appreciate the advantages of software as a service, but for those small and medium-sized enterprises and the ERP and CRM they need, software as a service is a boon. First of all, enterprises don't have to spend huge sums of money to buy the right to use software. Secondly, enterprises don't have to spend money to build computer rooms and hire people. Thirdly, enterprises do not have to consider the depreciation of machines and the upgrading and maintenance of software.