SOA World Magazine published an interesting article on the Five Pillars of Cloud Computing which does a pretty good job discussing the subject. From the article:
Cloud computing requires a dynamic computing infrastructure - there are four other pillars, too.
Cloud computing is getting tons of press these days. Everyone has a different perspective and understanding of the technology, and there are myriad variations on the definition of the cloud- William Fellows and John Barr at the 451 Group define cloud computing as the intersection of grid, virtualization, SaaS, and utility computing models. James Staten of Forrester Research describes it as a pool of abstracted, highly scalable, and managed compute infrastructure capable of hosting end-customer applications and billed by consumption. Let's take it a step further and examine the core principles, or pillars, that uniquely define cloud computing.
It's worth having a read - it's not too long, only one page!
ZeroTouch IT Ltd