The vCenter Server Appliance (vCSA) can be either downloaded as a single package (OVA); or the OVF, system disk, and data disk can be downloaded separately.
At the time of writing this book, the following were the names of the appliance files:
VMware-vCenter-Server-Appliance-5.1.0.5100-799730_OVF10.ova
Or
VMware-vCenter-Server-Appliance-5.1.0.5100-799730_OVF10.ovf
VMware-vCenter-Server-Appliance-5.1.0.5100-799730-system.vmdk
VMware-vCenter-Server-Appliance-5.1.0.5100-799730-data.vmdk
These names could possibly change when VMware releases the next update. I have included the file names only to give you a sense of what files have to be downloaded.