Cloud Computing services can be hosted on various models. The most important will be listed and described in this sub-chapter.
The service models are:
Software as a Service (SaaS)
SaaS is defined through the capability provided to the consumer to use the provider’s applications running on a cloud infrastructure. The consumer does not manage the underlying infrastructure with the possible exception of limited user specific application configuration settings.
Platform as a Service (PaaS)
A PaaS offering is giving developers the tools to build and host web applications. The cloud vendor delivers a ready configured platform which exposes an API for developers to run their tools.
Infrastructure as a Service (IaaS)
The IaaS approach is most likely the same as the traditional hosting solutions: The customer buy servers hosted at the vendor’s data center and then has to take care of the installation and management of the operating system and the applications himself.
Cloud Computing Deployment Models
Deployment models describe different scenarios where the services physically and legally are being hosted. Additionally, there are different ways of using and sharing a Cloud Computing offering. The officially defined deployment models are:
A private cloud is used when the cloud offering is operated solely for a single organization. The most important difference compared to a private data center is the fact that the using organization has no insights within the cloud operations and no rights and options to change or design these.
A community cloud is a service shared by several organizations that have shared concerns. In the commercial IT environment, a community cloud is rare; it is used in the private or academic sector.
Public cloud services are delivered to any customer who wishes to access it. There are no stipulations regarding the consumer’s ownership in using the cloud. It is provided to anyone who wishes to support the payment model.
A hybrid cloud is a mixture of the above. Sometimes the term hybrid cloud is also used when combining a cloud offering with a locally hosted solution.
The usage of the appropriate deployment model is highly dependent on the using organization size and business model. Small organizations which do not want to have IT staff at all, most likely will use public cloud offerings because of the high standardization and the low fees. Large enterprise might be able to leverage their existing datacenters in order to build up private cloud services, which can handle their custom service requirements and which are in a total cost of ownership (TCO) calculation cheaper than a public cloud offering. However, most medium and large size organizations will not be able to move all of their services into a cloud solution. Thus, the hybrid deployment model in practice will be the most common.
 Cp. Mantri, A; et. Al. (2011), p.4
 Cp. Gillam, L. (2010), p.4
 Cp. Gillam, L. (2010), p.3
 Cp. Halpert, B. (2011), p.9