VMware supports in-place upgrades on 64-bit systems from vCenter Server 4.x, vCenter Server 5.0.x, and vCenter Server 5.1 to vCenter Server 5.1.x.

Unlike versions before vCenter Server 5.1, vCenter Server 5.1.x does not support directly migrating an existing, 5.0.x or earlier vCenter Server to a new machine during an upgrade to version 5.1.x. You can migrate such an existing vCenter Server to a new machine during an upgrade to version 5.0, and then perform an in-place upgrade from version 5.0 to version 5.1.x See Upgrading to vCenter Server on a Different Machine.

vCenter Server 5.1.x can manage ESX 4.x/ESXi 4.x and ESXi 5.0.x hosts in the same cluster with ESXi 5.1.x hosts. vCenter Server 5.1.x cannot manage ESX 2.x or 3.x hosts.

Note

You cannot upgrade a vCenter Server 4.x instance that is running on Windows XP Professional x64 Edition to vCenter Server 5.1.x, because vCenter Server 5.1.x does not support Windows XP Professional x64.

vSphere 5.1 introduces vCenter Single Sign On service as part of the vCenter Server management infrastructure. This change affects vCenter Server installation, upgrading, and operation. See How vCenter Single Sign On Affects vCenter Server Installation and Upgrades.