I was interested in experimenting with Xen until I discovered that it has to be installed bare metal. Hence, if I have a Linux machine and want to use it to run a Xen hypervisor, I have to install the Xen server/kernel on the machine bare metal, and turn my host Linux into a VM of the Xen server!
I have used VirtualBox a lot before, where VBox sits "on top" of my host OS, allowing me to keep my Linux/Windows/whatever host, and run the hypervisor off of it.
I am wondering: which department does KVM fall into? Is KVM like Xen, where I have to install it bare metal, or can it be installed "on top of" an existing host (Windows/Linux) OS?