(1) Running applications in separate, isolated partitions (separate "virtual machines") within a single server. Widely used in enterprise and cloud computing datacenters, each virtual machine (VM) runs its own OS and application and can be moved or copied from one server to another for load balancing or to expand processing capability. Along with greater utilization of hardware, this "live migration" feature is one of the major benefits of using virtual servers. The Virtualization Tax The so-called virtualization tax is the additional overhead incurred from VMs running in a server. In a non-VM server, there is one copy of the operating system and all the applications. In a VM-based server, multiple operating systems are running, all of which are interacting with the VM infrastructure. As a result, more machine cycles are used than non-VM implementations. See virtual machine, I/O virtualization and cloud computing.
(2) Treating all servers in a network or server farm as a single resource. See network virtualization.