Cloud Computing - what ? why?

Some days before, I saw this word 'cloud computing' while reading
an article in net. Now, got some time to look into this topic as phase
3 release of my project has been successfully done on schedule. :)

This technology is not new to many of us but the word sounds
interesting. Infact, we all are using this one or the other way!!!

Cloud is what which hides back screen from our eyes. It is used
to describe a layer of seperation here. So, computing behind screens
is cloud computing !!! .. :)

Now we will get on to technical definition of cloud computing .....

“A style of computing where scalable and elastic IT-related
capabilities are provided ‘as a service’ to external customers
using Internet technologies.”

1. Service based -> Defined interfaces between consumers and
providers
2. Scalable & elastic -> Scales to add or remove resources, as needed
3. Shared -> Shares a pool of resources for economy of scale
4. Metered by use -> Tracks usage and enables multiple payment
models
5. Internet tech -> Is delivered through Internet formats and
protocols

When you start digging more into this topic we definitely come across
Iaas, Paas and Saas ! what are they ?

Iaas : IT Level “Infrastructure-as-a-Service” where only
infrastructure was provided as service includes System administration,
obtain general processing, storage, database management,
and other resources and applications through the network and pay only
for what gets used.
ex: Amazon Web Services, Google Base …

Paas: Developer Level “Platform-as-a-Service” where Developers
can design, build and test applications that run on the Cloud provider’s
infrastructure and then deliver those applications to end-users from
the providers servers.
ex: Microsoft Windows Azure, Yahoo developer network, Google
App Engine, …

Saas: User Level “Software-as-a-Service” where Companies host
applications in the cloud that many users access through internet
connections. The services being sold or offered is a complete end-user
application.
ex: Google Docs, acrobat.com, Oracle on demand, Windows Office Live, …

Now, I think no need to explain why we need this !!!!!!!!!!!!!!!!