"The main idea behind the cloud is that you can access all your information over the internet without having any detailed knowledge of the infrastructure used to enable it. Do individuals really need to know about such detail? Just like we don’t really need to know what the phone company or electric company does on their end to enable calls and allow the lights to go on when you flip the switch; and, you really don’t want to know as long as when you plug into it, it works. Cloud, for companies with business critical applications running therein, can be described in the same way.
Cloud computing can be divided into three general models: public cloud, private cloud and hybrid cloud. Public cloud consists of independent, third-party service providers that rent or lease cloud computing resources to external clients, such as businesses or government agencies. A private cloud represents the deployment of on-premises cloud services, generally building upon an existing virtual data-centre infrastructure with self-service portals, chargeback or showback models and additional services, such as automated provisioning or resource scalability. A hybrid cloud connects both public and private cloud services, allowing a business to use both environments simultaneously while shifting workloads between private and public cloud facilities on demand."