Simple explanation of the three ways to cloud compute(by Christopher Barnatt)

[Perspective of XaaS]
- Allow users to run applications and store data online.

- Each offers a different level of user flexibility and control.

[SaaS]
- Simple definition : Allows users to run existing online applications. Where off-the-shelf applications are accessed over the internet.

- Pros & Cons

Free or paid via subscription.

Accessible from any computer.

Facilitates collaborative working.

Generic applications not always suitable for business use.

[PaaS]

- Simple definition : Allows users to create their own cloud applications using supplier-specific tools and languages. Provides environment and tools for creating new online applications

- Pros & Cons

Rapid development at low cost.

Private or public deployment.

Limits developers to provider languages and tools.

Risk of vendor lock-in.

[IaaS]

- Simple definition : Allows users to run any applications they please on cloud hardware of their own choice. Allows existing applications to be run on a cloud supplier's hardware.

- Pros & Cons

Use computing power at low cost anywhere can access internet.

Security issue.

- Type

Private Cloud.

Dedicated Hosting.

Hybrid Hosting.

Cloud Hosting.

For more detail information & video :
 

http://www.explainingcomputers.com/cloud/BGT_Cloud_Computing_Extract.pdf