vSphere 6.5 provides many options for upgrading your vSphere deployment. For a successful vSphere 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 Linux OS--based virtual machine optimized for running the vCenter Server system and the vCenter Server components.
Starting with vSphere 6.0, important required services for running vCenter Server and the vCenter Server components are included in the Platform Services Controller.
Based on your existing vCenter Server configuration details, you can upgrade to one of the following deployment types:
vCenter Server with an embedded Platform Services Controller.
vCenter Server with an external Platform Services Controller.
You cannot change your vCenter Server deployment type during upgrade.