Hosts and clusters are providers of physical resources.

For hosts, available resources are the host’s hardware specification, minus the resources used by the virtualization software.

A cluster is a group of hosts. You can create a cluster using VMware® vCenter Server, and add multiple hosts to the cluster. vCenter Server manages these hosts’ resources jointly: the cluster owns all of the CPU and memory of all hosts. You can enable the cluster for joint load balancing or failover. See Creating a DRS Cluster for more information.