If you aren't exactly up to speed with what KVM is, you probably aren't alone. And yet, as obscure as it is, it seems like it came out of nowhere to beat Xen and other virtualisation solutions to the Linux kernel.
KVM stands for Kernel-based Virtual Machine, and it has been accepted by the kernel guru himself, Linus Torvalds, for inclusion in the Linux kernel version 2.6.20.
KVM is a full virtualisation solution for Linux on x86 hardware and it consists of a loadable kernel module (kvm.ko) and a user space component. KVM is open source software and is licensed under the GNU General Public License.
KVM hasn't been around very long. It was only introduced back in October. But because of its small size and simplicity, the product has made a lot of progress in a short amount of time.
In order to operate with KVM, you will need an x86 machine running a recent Linux kernel on an Intel processor with VT extensions or an AMD processor with SVM extensions or AMD-V.
Where Xen is an external hypervisor, it assumes control of the machine and divides resources among guests. KVM on the other hand is part of Linux and uses the regular Linux scheduler and memory management. This makes KVM much smaller and more simple to use. Unfortunately, there is a trade-off to be made here. KVM doesn't currently support the para-virtualisation technique found in Xen, where modified guest operating systems can run with near native performance.
KVM currently supports 32- and 64-bit hosts, and any combination of PAE and non-PAE guests and hosts. The only unsupported combination is a 64-bit guest on a 32-bit host.
You can find out more information about the product, here.