Most applications running on a server can easily share a machine with others, if they could be isolated and secured. Further, in most situations, different operating systems are not required on the same server, merely multiple instances of a single ''operating system''. OS-level virtualization systems have been designed to provide the required isolation and security to run multiple applications or copies of the same OS (but different distributions of the OS) on the same server. [http://openvz.org/ OpenVZ], [http://linux-vserver.org/ Linux-VServer] and [http://www.sun.com/bigadmin/content/zones/ Solaris Zones] are examples of OS-level virtualization.

The three techniques differ in complexity of implementation, breadth of OS support, performance in comparison with standalone server, and level of access to common resources. For example, VMs have wide scope of usage, but poor performance. Para-VMs have better performance, but can support fewer OSs because of need to port original OSes.