Some of the key differences between vSphere 5.1 and vSphere 5.5 Features vSphere 5.1 vSphere 5.5 Physical RAM per host 2  TB 4 TB Physical CPUs per host 160 320 Maximum vCPUs per host 2048 4096 VMDK Size 2TB 62 TB Max Size of Virtual RDM 2TB 62 TB VM Hardware Version 9 10 ESXi