OpenVz is is a linux based virtualization platform based on the linux operating systems such as Centos, Fedora, Gentoo, and Debian, but OpenVZ users are not able to make any kernel modifications. However because it doesn’t have the overhead of a true hypervisor it is very fast and efficient over Xen, KVM. If you are looking for a fast, affordable and good VPS solution (memory, disk space, bandwidth, etc.), OpenVZ is for you. KVM, Stands for Kernel-based Virtual Machine is another hypervisor that is in the mainline Linux kernel. Your host OS has to be Linux but it supports Linux, Windows, Solaris, and BSD guests. It runs on x86 and x86-64 systems with hardware supporting virtualization extensions (Intel VT or AMD-V). It consists of a loadable kernel module, so that KVM provides the core virtualization infrastructure and a processor specific module. Xen is also a hypervisor like ovz and kvm, over-selling is not allowed in XEN, but the good thing its open source software.