KVM = Kernel-based Virtual Machine
It seems that a sort of hypervisor is going to be added to the mainline Linux kernel. It has been dubbed KVM... as if KVM weren't already taken by "Keyboard, Video Mouse". In this case, KVM stands for Kernel-based Virtual Machine... and it only works in CPUs that have VT (Intel) or AMD-V/SVM (AMD) extensions via a module named kvm.ko... and will available upon the release of the 2.6.20 kernel.
How does it differ from other virtualization schemes? From the FAQ:
What is the difference between kvm and Xen?
Xen is an external hypervisor; it assumes control of the machine and divides resources among guests. On the other hand, kvm is part of Linux and uses the regular Linux scheduler and memory management. This means that kvm is much smaller and simpler to use.
On the other hand, Xen supports both full virtualization and a technique called paravirtualization, which allows better performance for modified guests. kvm does not at present support paravirtualization.
What is the difference between kvm and VMWare?
VMware is a proprietary product. kvm is Free Software released under the GPL.
What is the difference between kvm and QEMU?
Qemu uses emulation; kvm uses processor extensions for virtualization.
And now for the question everyone wants to ask:
What OSs can I run inside kvm VM?
We have tested Linux (32/64 bit) and Windows (32 bit). Others may or may not work. 64-bit Windows is known not to work. This will be fixed once qemu-0.8.3 is released and merged. Several Linux flavors are known to hang on Intel processors during startup. Workaround is to disable splashscreens in grub.
I wonder how long before this becomes part of all of the distributions... and how it might conflict with Xen???