Platform as a Service methods provide a computing platform in the "cloud" that is typically managed, at least to some degree, by the Cloud Service Provider. Typically the Platform as a Service user would decide to use Linux, UNIX, Microsoft Windows etc to be installed on the Cloud Service Provider's virtual platform.
Platform as a Service makes the development, testing, and deployment of applications quick, simple, and cost-effective. With this technology, enterprise operations, or a Cloud Service Provider, can manage Operating Systems, virtualization, servers, storage, networking, and the PaaS software itself. Developers, however, manage the applications.