Introduction
Cloud computing means using the computing resources both hardware and software, that are delivered as a service over Internet. In other words, computer and software services necessary for computing works provided via the internet is called cloud computing.

When we think about the need of IT, cloud computing comes into focus like the requirement of a way to increase or add capabilities on the fly without investing in new infrastructure, training new personnel, licensing new software etc. Cloud computing encompasses any subscription-based or pay-per-use service that, in real time over the Internet, extends IT’s existing capabilities.
Cloud Computing is a technology that uses the internet and central remote servers to maintain data and applications. Cloud computing allows consumers and businesses to use applications without installation and access their personal files at any computer with internet access. This technology allows for much more efficient computing by centralizing data storage, processing and bandwidth.

It is named as cloud computing because all the services are provided via the internet and cloud symbol is used as an abstraction for the complex infrastructure it contains in system diagrams. Cloud computing entrusts remote services with a user's data, software and computation.

There are three types of services offered in cloud computing
Infrastructure as a service In Infrastructure as a service, the service provider provides the necessary servers, hardware and networking components to an organization for a fee. The organization in turn installs the necessary programs in the service provider's server and uses them. The service provider is responsible for the maintenance of the servers.

Platform as a service In Platform as a service, the service provider provides the necessary softwares and the tools for creating softwares which are installed in their server to an organisation for a specified amount. The organization creates the necessary softwares on his platform and uses them. Its like renting in a house which has all the necessary things.

Software as a service In Software as a service, the applications hosted in the service provider’s server are made available to customers via the internet. The provider also interacts with the user through a front end panel. The provider provides the necessary support to the customer. The services range from e-mail to data processing.

Advantages of cloud computing The main advantage of cloud computing is that the customer can get the service at any time.

Also there are no problems of computer crash or server down. All the responsibility is of the service provider.
There is no investment cost for computers, servers, software, etc..
Amount can be paid according to usage.

Now days, the service providers provide the service on a monthly basis. The provider and the customer can cancel the agreement at any time.

5 Disadvantages of Cloud Computing

Possible downtime - Cloud computing makes your small business dependent on the reliability of your Internet connection. When it's offline, you're offline. And even the most reliable cloud computing service providers suffer server outages now and then
Security issues - How safe is your data? Cloud computing is Internet computing. So you should not be using cloud computing applications that involve using or storing data that is private and confidential. That being said, established, reliable cloud computing vendors will have the latest, most sophisticated data security systems possible as they want your business and realize that data security is a big concern.
Cost - At first glance, a cloud computing application may appear to be a lot cheaper than a particular software solution installed and run in-house, but you need to be sure that cloud application have all the features that the software does and if not, are the missing features important to you?
Inflexibility - Be careful when you're choosing a cloud computing vendor that you're not locking your business into using their proprietary applications or formats.
Lack of support - Customer service for Web apps leaves a lot to be desired -- All too many cloud-based apps make it difficult to get customer service promptly – or at all. Sending an email and hoping for a response within 48 hours is not an acceptable way for most of us to run a business".