vCenter Server 7.0 provides many options for upgrading your vCenter Server deployment. For a successful vCenter Server upgrade, you must understand the upgrade options, the configuration details that impact the upgrade process, and the sequence of tasks.
The two core components of vSphere are VMware ESXi™ and VMware vCenter Server™. ESXi is the virtualization platform on which you can create and run virtual machines and virtual appliances. vCenter Server is a service that acts as a central administrator for ESXi hosts connected in a network. You use the vCenter Server system to pool and manage the resources of multiple hosts. vCenter Server appliance is a preconfigured virtual machine optimized to run vCenter Server.
You can upgrade existing vCenter Server deployments that include either an embedded or an external Platform Services Controller to a deployment consisting of a vCenter Server appliance.