VMDirectPath vs. Paravirtual SCSI

Below posting was referenced.
http://professionalvmware.com/2009/08/vmdirectpath-paravirtual-scsi-vsphere-vm-options-and-you/

Paravirtual SCSI is feature supported by guest OS. So it requires guest OS modified to support paravirtual SCSI adaptor. See http://kb.vmware.com/kb/1010398 for supplement information on Paravirtual SCSI.

VMdirectPath device can be connected up to 2 (for ESX4.0) or 4 devices(from ESX 4.1). Refer http://kb.vmware.com/kb/1010789 This feature requires CPUs that support directed I/O such as Intel's VT-D technology and AMD's AMD-Vi originally called IOMMU-input/output memory management unit. Refer http://www.intel.com/technology/itj/2006/v10i3/2-io/7-conclusion.htm for more on VT-D.