Private clouds take two forms: internal clouds and external private clouds. An internal cloud is inside your data center (on-premises), giving IT managers complete control over the available resources. A typical internal cloud relies on the security measures available within the cloud and within your data center. Ubuntu Enterprise Cloud and Microsoft Azure are examples of packaged software for creating internal clouds.
External private clouds combine characteristics of internal clouds and public clouds. They are like public clouds because they are off-premises. But unlike public clouds, applications run on dedicated servers, and the cloud provider has built container walls around the external private cloud to make it more secure than public clouds. IT managers have more control over the resources in a private cloud than over resources in a public cloud. Amazon's Virtual Private Cloud is an example of an external private cloud.
"Clouds provide automation and orchestration not found with server virtualization," says Jeff Deacon, cloud computing principal for Verizon Business. (Although Deacon's day job is helping figure out which of Verizon's internal applications should go on the cloud, his company also sells a public-cloud offering called Computing as a Service.)
In other words, Deacon says, cloud computing involves imposing a layer of abstraction between the applications and servers -- physical or virtual -- that automates many tasks typically done manually.
"Clouds can be viewed differently, depending on what you want from a cloud," adds David Escalante, director of IT security at Boston College. "We view cloud computing as running software applications that you would normally run in your own data center in someone else's data center. It is very important to create a definition of cloud computing for your organization." Armed with that definition, Boston College can focus on determining whether cloud computing is right for its data center needs, and which applications can be run on clouds.
Because clouds are based on virtualization, applications have to be virtualized before being moved to any of the cloud environments. But some cloud vendors can help with this, especially if the vendor supports a specific hypervisor.