Nowadays, a new model is appearing, this is cloud computing. Most businesses today do not need to buy data center hardware such as servers because they are affordably rented on a short term basis from a hosting company that provide turnkey implementations of web applications. In cloud computing model web applications are software as a service (SaaS). There are business applications provided as SaaS for enterprises for fixed or usage dependent fee. Other web applications are offered free of charge, often generating income from advertisements shown in web application interface. We could think about some popular sites which are using this philosophy, like DropBox, Google Applications, ... etc.

Cloud computing refers to both the applications delivered as services over the Internet and the hardware and systems software in the data centers that provide those services. The data center hardware and software is what we will call a cloud. When a cloud is made available in a pay-as-you-go manner to the general public, we call it a public cloud; the service being sold is utility computing. We use the term private cloud to refer to internal data centers of a business or other organization, not made available to the general public. However, this topic could serve as a standalone theme for a book, so its not discussed further here.