Definitions of cloud computing vary, but, until recently, most centered around the concept of moving computing functionality from behind corporate firewalls onto the internet. A computing task moved to the cloud becomes a service provided by a third party in its own data center, allowing companies to scale down their huge investments in IT hardware, software and staff.
So the advent of the term "private cloud" may strike you as an oxymoron, because it keeps much of the IT action behind a company's firewall - and much of the expense on its books.
But many companies, particularly large ones, are moving more avidly toward private clouds than toward public ones. (Gartner forecasts that, through 2012, the top 1,000 global corporations will spend more on building private clouds than on buying public-cloud services.) Some, in fact, may be moving that way without even realizing it.
