Cloud computing is typically classified in two ways:
Location of the cloud computing
Type of services offered
Cloud computing is typically classified in the following three ways:
Public cloud: In the Public cloud, the computing infrastructure is hosted by the cloud vendor at the vendor’s premises, it is open for public use.
Private cloud: The computing infrastructure is dedicated to a particular organization and not shared with other organizations. Private clouds are more expensive and more secure when compared to public clouds.
Hybrid cloud: It is a combined hosting of two or more clouds. Organizations may host critical applications on private clouds and other applications on the public cloud. The entities are unique but are bound together.
Community cloud: Involves sharing of computing infrastructure in between organizations of the same community.
Based upon the services offered, clouds are classified in the following ways:
Infrastructure as a service (IaaS): Involves offering virtual machines, abstracted hardware and operating systems using the principles of cloud computing. As the name implies, only the infrastructure is purchased while the software is owned by the user. Leading vendors that provide Infrastructure as a service are, Amazon EC2, Amazon S3, Rackspace Cloud Servers and Flexiscale.
Platform as a Service (PaaS): Involves offering a development platform, configuration management on the cloud. Platforms provided by different vendors are typically not compatible.Examples include Googles Application Engine, Microsoft's Azure, Salesforce.com, force.com.
Software as a service (SaaS): Provides complete software offering on the cloud. Users can use on-demand basis, e.g. Salesforce.com, Google cs and Microsoft online version of office called BPOS (Business Productivity Online Standard Suite).