Red Hat announced a new bare-metal hypervisor technology last week at the Red Hat Summit in Boston. It is based on KVM (Kernel-Based Virtual Machine) technology and actually has been included in Linux kernel version 2.6.20 and up. This announcement has some Red Hat and virtualization proponents wondering why Red Hat is throwing its support behind this solution when it already includes Xen technology.

Xen is true hypervisor virtualization; KVM is not. KVM is hosted virtualization that employs QEMU for virtual machines.

Red Hat may be pushing this KVM solution to allow more users to try an entry-level bare metal virtualization solution. There is much debate amongst virtualization professionals about why Red Hat is doing this and why they are calling a non-hypervisor virtual machine builder a hypervisor. My guess is that they are calling it a hypervisor because it is installed on bare metal. Bare metal refers to a server system that has no operating system on it.

For production-level virtualization, you should still stick with Xen or another true hypervisor technology. This KVM-related solution is still in beta and will take a while to become a viable option for those who wish to use it in limited production environments.

If you want to try this new KVM-based pseudo-hypervisor technology, go to and download the Proxmox VE. Let me know what you think of it. To try one of the Xen products, go to the Citrix Xen site. See for yourself how a true hypervisor performs.

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"KVM is hosted virtualization that employs QEMU for virtual machines. "

With the Xen model QEMU runs on top of the Domain0 operating system (Linux or Solaris). A modified QEMU is used to provide the device model to the guests. Does this make Xen "hosted".

"Bare metal refers to a server system that has no operating system on it."
The Xen hypervisor requires a Domain0 (Linux or Solaris) - you can't run Xen without one.

The difference here seems to be that with KVM the hypervisor piece is inside the operating system kernel, but with Xen the hyervisor site underneath the operating system.

If you're looking for a solution with no operating system then it's VMware 3i - but even that actually has Linux device drivers.