Processors have evolved to improve performance for virtualized environments. But a commodity I/O device has no support for virtualization. A VMM can assign such a device to a single guest with direct, fast, but insecure access by the guest's native device driver. Discover one such I/O performance enhancement called device pass-through. With the technology, the guest operating system can use the hardware device as if it were a non-virtualized system. In this paper, the authors describe the innovation and present preliminary results how to improve performance of PCI devices using hardware support from Intel (VT-d) or AMD (IOMMU).