We are planning on upgrading soon to version 6.5. I am looking at the instructions at https://docs.vmware.com/en/VMware-vSphere/6.5/com.vmware.vsphere.upgrade.doc/GUID-A3566E1A-5C64-46E5..., and I noticed that one of the steps is to "Download and Mount the vCenter Server Appliance Installer". I am wondering if that is necessary when upgrading vCenter Server 5.5 on Windows to vCenter Server 6.5 on Windows, and what the purpose of that would be if it is necessary. We do not currently use the appliance nor do we intend to.
I knew something was happening, but didn't realize the scope of it. That link changed my whole calculus about this upgrade. I'll probably be going to the appliance now.