What are the different types of Cloud Service Providers in Salesforce?

Example of Cloud Service providers:

Amazon and Rackspace. Other major cloud service providers include Cisco, Citrix, Google, IBM (SoftLayer), Oracle, Microsoft (Azure), and SAP, Rackspace, and Verizon (which acquired Terremark).
Rackspace, who started as a web hosting company and buy either PAAS or IAAS services. Many cloud providers are focusing on specific verticals, such as hosting healthcare applications in a secure IAAS environment.

Cloud service providers (CSP) are companies that offers network services, infrastructure, or business applications in the cloud. The cloud services are hosted in a data center than can be accessed by companies or individuals using network connectivity.Cloud Service Providers are those who provide cloud services to the business and customers or consumers. Cloud Service providers will have huge data base, Data centers, infrastructure, software’s, platform and hardware systems.

The large benefit of using a cloud service provider comes in efficiency and economies of scale. Rather than individuals and companies building their own infrastructure to support internal services and applications, the services can be purchased from the CSP, which provide the services to many customers from a shared infrastructure.
There are several different forms of services that can be used “in the cloud” by CSPs, including software, often referred to as Software as a Service (SaaS), a computing platform for developing or hosting applications, known as Platform as a Service (PaaS); or an entire networking or computing infrastructure, known as Infrastructure as a Service (IaaS). The divisions, however, are not always clear-cut, as many providers may offer multiple flavors of cloud services, include traditional web or application hosting providers.