The next category of cloud computing is Platform as a Service (PaaS). It provides a platform and environment that allows customers to develop, run, and manage applications and services over the internet.  Like IaaS, PaaS provides the entire infrastructure associated with development and launch of applications. PaaS services are hosted in the cloud and accessed by the users through web browsers.

Originally PaaSes were in the public cloud. Later on companies demand private and hybrid PaaS options were created. Enterprises of all sizes have endorsed PaaS solutions for simplifying their systems and making them more reliable. These days, PaaS is the most trusted model for running applications in the companies. As this will prevents them from botheration of infrastructural (hardware and software) maintenance. PaaS is leading a new era of innovation business promptitude

1. Public cloud service- In this the services are consumer oriented this means that the software to be deployed is controlled by consumer with the minimal configurations. 

2. Private cloud service- In this the services are provider oriented which means the provider develops the software and deploy it on public infrastructure. 

PaaS offers the facilities for design, development, testing and deployment of applications. It also provides services like web service integration, state management, application instrumentation, monitoring, storage, persistence and many more.

- Google App Engine

- Engine Yard

- Sales force.com

- AppFog

- Caspio

- Grid Gain

1. Abstraction- With PaaS the consumer needs to manage the application and data only while the provider or IT department manages the deployment and infrastructure configurations. 

2. Runtime Framework- The policies according to which end user code is executed are set by application owner and cloud provider in the PaaS runtime frame work. PaaS runtime frameworks come in many flavors.

3. Reduced complexity- PaaS allows high-level programming at developers end with less complexity due to in built infrastructures.in addition to this maintenance and enhancement of the application is also easy.

4. Speed and flexibility- As developer whole focus is on the application the work time reduced to a great extent. Beside this the user can customized the development tools according to his needs . this makes the system flexible.

Beside these features PaaS supports all the IaaS characteristics too like scalability, reliability, disaster recovery, cost effectiveness,.

* Apprenda-  Apprenda’s firms  PaaS for Java and .NET. By using PaaS, productivity and savings both boost up because app development teams need not to focus on internal infrastructures. In addition to this the updated and modern applications are available and at faster speed.

* Pivotal CFTM – Pivotal is a huge data and application enterprise PaaS vendor where subsidiaries like VMware, EMC owns the PaaS. But Pivotal CFTM is a proprietary enterprise PaaS based on Cloud Foundry.

* Red Hat Ope Shift – it is an open source enterprise PaaS (CEAP) which is not based on Cloud Foundry. Red Hat its own public PaaS version of OpenShift and added it on Red Hat Enterprises LINUX, JBoss, OpenStack stack.

The limitations of PaaS are very few

- One of them is that the developer is not able to use full range of conventional tools for example relational databases with unrestricted joins

- Another disadvantage is that one can be locked-in to certain platforms.  How ever most PaaSes are lock-in free.

Thus, application of PaaS has revolutionized the IT Industry and has opened new doors of opportunities for Global development.

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