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Once you have multiple hypervisors, you can add additional functionality, such at the ability to move VMs from one server to another, either to keep overall loads balanced, or to consolidate loads on one server and shut down others. Hypervisors can also be configured to run in clusters, so that if one server fails, the VMs are automatically moved to other servers in the cluster. VMWare and Microsoft both offer specialized software for managing VMs across multiple servers, as well as for clustering and failover situations.