Red Hat RHEL 5 KVM & Xen unconfusion !
now includes full support for the Kernel-based Virtual Machine (KVM) hypervisor on x86_64 based architectures. KVM is integrated into the Linux kernel, providing a virtualization platform that takes advantage of the stability, features, and hardware support inherent in Red Hat Enterprise Linux.
Note Xen is the default hypervisor that is shipped with Red Hat Enterprise Linux. As such all configuration defaults are tailored for use with the Xen hypervisor. For details on configuring a system for KVM, please refer to the Virtualization Guide. Important Xen based virtualization is fully supported. However, Xen-based virtualization requires a different version of the kernel to function. The KVM hypervisor can only be used with the regular (non-Xen) kernel. Warning While Xen and KVM may be installed on the same system, the default networking configuration for these are different. Users are strongly recommended to only install one hypervisor on a system.