What is Cloud computing?

Aside from the latest marketing term?

Basically all the resources your program needs are held "somewhere" on the internet. You interact with them via a defined service contract; SOAP, REST, POX or whatever and what happens after that is up to the service provider. You don't care about how your information is stored or how the service is provided, just that it is.

If, for example, you wanted to store files, you may choose to use Amazon's S3 cloud system. You connect to the service and upload your files; you don't know or care where the files are stored, only the location of the entry point to that service.

If you have an application then it may also be ran in the cloud, assuming it's suitable. Live Mesh for example is a virtual machine which you can code against and run your software both locally and within the cloud, so your user simply goes to a URI and finds your program, you don't care where it is beyond it being available somewhere on the cloud.

Cloud computing is about hardware-based services (involving computing, network and storage capacities), where:

• Services are provided on-demand; customers can pay for them as they go, without the need to invest into a datacenter.
• Hardware management is abstracted from the customers.
• Infrastructure capacities are elastic and can easily scale up and down.

There is a powerful economic force behind this simple model: providing and consuming cloud computing services generally allows to have far more efficient resource utilization, compared to self-hosting and data center type of hosting.

Snippet from this article on cloud computing.

The term is so new that there's no accepted definition, particularly since Dell (!) failed to trademark the term.

Essentially the idea is similar to that of a utility - you want electricity, but you don't care which power station supplies it because there's a network supplying electricity to everyone, and you can just tap into it. Which works for electricity, but the Internet isn't quite that sophisticated just yet. But that's the Vision.

Amazon's S3 service just provides disk space, and it doesn't care who uses it or where they are located in the world. Certainly Google's office tools (and Microsoft's web offering) offers a service, not a particular machine, which will look after your application needs. Again, you can create and work with a spreadsheet but you don't know where that spreadsheet is stored, or which machine it runs on - just that it's available when you want it.

Web 2.0 is another term struggling to find a definition, but you can imagine your spreadsheet using calculations which are embedded in another machine somewhere, and storing results of its calculations on Amazon S3. Boundaries are fading away at this point.

Because it's available wherever you log in from, it could be accessed from anywhere in the world. It's "in the cloud" because it can be seen from anywhere (not a good analogy, but ...)

Even something simple such as webmail can be considered to hold our information "in the cloud". That is to say that the data isn't held locally, it's stored on that magical cloud thing called the internet.

It's basically just a buzzword for storing stuff remotely. This list summarises why it's used.

FTP backup => Storing files in the cloud
SSHing into a remote PC to execute code => Cloud computing
Webmail => Cloud mail
SSHing into a remote PC to execute code that predicts the weather => Cloud computing via Cloud computing

(I tried an html table but it didn't render...)

Sounds cooler doesn't it!

Cloud computing is a type of shared computing where one utilizes large-scale computing infrastructure. In other words, powerful hardware is interlinked, often to fully realize the benefits of virtualization. This hardware can be shared among many users in the form of a public cloud or dedicated to one entity as it is used in private cloud computing.

The public cloud is defined as a multi-tenant environment, where you buy a “server slice” in a cloud computing environment that is shared with a number of other clients or tenants.

Private cloud computing, on the other hand, by definition is a single-tenant environment where the hardware, storage and network are dedicated to a single client or company.

It is a computing that happens in distributed on the Internet. The idea is that instead of creating your own resources, you put your data,apps in a Cloud. This cloud is assumed to have 100% availability, and infinite scalability. For more detail :http://vineetgupta.spaces.live.com/blog/cns!8DE4BDC896BEE1AD!1326.entry

i suggest you to read this paper

Above the Clouds: A Berkeley View of Cloud Computing, armbust at all

There will be no doubt on your mind.And in research area this paper is referred as introduction to cloud computing