The infrastructure that supports virtual machines consists of at least two software layers, virtualization and management. In vSphere, ESXi provides the virtualization capabilities that aggregate and present the host hardware to virtual machines as a normalized set of resources. Virtual machines can run on an isolated ESXi host or on ESXi hosts that vCenter Server manages.

vCenter Server lets you pool and manage the resources of multiple hosts and lets you effectively monitor and manage your physical and virtual infrastructure. You can manage resources for virtual machines, provision virtual machines, schedule tasks, collect statistics logs, create templates, and more. vCenter Server also provides vSphere vMotion ™, vSphere Storage vMotion, vSphere Distributed Resource Scheduler (DRS), vSphere High Availability (HA), and vSphere Fault Tolerance. These services enable efficient and automated resource management and high availability for virtual machines.

The VMware vSphere Web Client and the vSphere Client are interfaces to vCenter Server, ESXi hosts, and virtual machines. With the vSphere Web Client and the vSphere Client, you can connect remotely to vCenter Server. With the vSphere Client you can also connect directly to ESXi from any Windows system. The vSphere Web Client and the vSphere Client are the primary interfaces for managing all aspects of the vSphere environment. They also provide console access to virtual machines.

The vSphere Web Client and the vSphere Client present the organizational hierarchy of managed objects in inventory views. Inventories are the hierarchal structure used by vCenter Server or the host to organize managed objects. This hierarchy includes all of the monitored objects in vCenter Server.

In the vCenter Server hierarchy, a datacenter is the primary container of ESXi hosts, folders, clusters, resource pools, vSphere vApps, virtual machines, and so on.

Datastores are virtual representations of underlying physical storage resources in the datacenter. A datastore is the storage location (for example, a physical disk or LUN on a RAID, or a SAN) for virtual machine files. Datastores hide the idiosyncrasies of the underlying physical storage and present a uniform model for the storage resources required by virtual machines.

For some resources, options, or hardware to be available to virtual machines, the host must have the appropriate vSphere license. Licensing in vSphere is applicable to ESXi hosts, vCenter Server, and solutions. Licensing can be based on different criteria, depending on the specifics of each product. For details about vSphere licensing, see the vCenter Server and Host Management documentation.