Having spent the last 7 years listening to people using #Linux
in their datacenter and then trying to teach my IBM Power colleagues about scale-out computing, I have to pass along one of the best tips I received a little over a year ago. If you want to understand cloud and scale-out, read this book, "The Data Center as the Computer."
Don't let the sub-title reference to warehouse-scale computing scare you. The concepts of why scale-up eventually breaks down and how investing in software is more economical than buying specific-function systems (typical in scale-up computing) apply wholly to the revolution of scale-out. Many old UNIX junkies find this argument hard to understand but the folks at Google layout all the arguments.
Oh, and those arguments apply to any size data center once the software becomes architected to handle any resources available to it. Now, tie in open source software which can be leveraged by all, and the potential is limitless. THIS is the revolution occurring in datacenters around the world -- Linux, KVM, OpenStack, ....
Find the book and read it if you REALLY want to understand cloud and scale-out.