* Services are multi-tenant (many customers leverage the platform).

The ability to customize a service is limited.

The cloud lets users contract for services at three levels:

• Infrastructure as a Service : Grids of virtualized servers, storage & networks. Examples include Amazon's Elastic Compute Cloud and Simple Storage Service.

* Platform-as-a-service: The abstraction of applications from traditional limits of hardware allowing developers to focus on application development and not worry about operating systems, infrastructure scaling, load balancing and so on. Examples include Force.com and Microsoft's Azure investments.