The main difference between private and public cloud infrastructures is that a private system is used only to house and distribute your data and applications, while a public model is used to serve the requirements for multiple organizations, not just yours. When we think of computer resources in the cloud, we usually think of public clouds, such as the ones offered by Google, Amazon, Microsoft, with infrastructure or applications shared by millions of clients worldwide, through the Internet. Cloud computing has proven to be a good alternative for companies, because it reduces costs and generates flexibility. But security and availability issues still need to be resolved. That is why more and more companies are choosing private clouds. Some organizations, because of their organizational cultures or for security or regulatory concerns, cannot move directly into public clouds, but they have the option of private clouds. Banks, Govt. sectors, for example, cannot join public, Internet-access clouds.
Organizations that need greater security will have to invest in private clouds, but they also need to be sure that they can rely on the availability and performance of services. One main advantage of private cloud infrastructures is that they are usually more secure than alternatives, since the organization’s data is tightly secured and controlled on servers that no other company has access too. But again security factor is totally depending on that organization that is which type of security they are providing to that. Private cloud is characterized by flexibility, flexibility that is achieved by on-demand self-service, resource pooling and a measured service. This means that end users, which can be departments or business units, are responsible for their own computing resource needs rather than the IT departments. The IT department is responsible for the overall infrastructure but no longer for the individual resources. End users can create their own resources, have to pay for its usage and can destroy resources when no longer needed.