[caker]

There's no such thing as a "cloud server" that sits atop a cluster of machines and pools resources together like RAM into a single instance. VPS and Cloud Servers are identical. It's just marketing. TO THE CLOUD!

Any virtualized Linux instance boils down to a VM running on a single host server. This is true at Linode, Amazon, Rackspace Cloud Servers, etc.

Xen and KVM instantiate a virtualized kernel per VM. Virtuozzo is a container/enhanced jail and runs under the host's kernel.