Cloud computing is a general term for anything that involves delivering hosted services over the Internet. These services are broadly divided into three categories:
- Infrastructure-as-a-Service (IaaS)
- Platform-as-a-Service (PaaS)
- Software-as-a-Service (SaaS)
The name cloud computing was inspired by the cloud symbol that's often used to represent the Internet and as a service it has three distinct characteristics:
- it is sold on demand, typically by the minute or the hour
- it is elastic, a user can have as much or as little of a service as they want at any given time
- the service is fully managed by the provider (the consumer needs nothing but a personal computer and Internet access)
Significant innovations in computing, improved access to high-speed Internet and a weak economy, have accelerated interest in cloud computing. It can be private or public, the goal however is to provide easy, scalable access to computing resources and IT services.
- Infrastructure-as-a-Service like Amazon Web Services provides virtual server instance API to start, stop, access and configure their virtual servers and storage. Cloud computing allows a company to pay for only as much capacity as is needed, and bring more online as soon as required. Because this pay-for-what-you-use model resembles the way electricity, fuel and water are consumed, it's sometimes referred to as utility computing.
- Platform-as-a-Service in the cloud is defined as a set of software and product development tools hosted on the provider's infrastructure. Developers create applications on the provider's platform over the Internet. PaaS providers may use APIs, web site portals or gateway software installed on the customer's computer. Force.com and GoogleApps are examples of PaaS. Developers need to know that currently, there are not standards for interoperability or data portability in the cloud. Some providers will not allow software created by their customers to be moved off the provider's platform.
- In the Software-as-a-Service cloud model, the vendor supplies the hardware infrastructure, the software product and interacts with the user through a front-end portal. SaaS is a very broad market. Services can be anything from Web-based email to inventory control and database processing. Because the service provider hosts both the application and the data, the end user is free to use the service from anywhere.