VT-d

Milligan explained that VT-D aims to improve performance by letting guest OSes talk directly to real hardware, rather than to the emulated hardware devices exposed by most enterprise virtualization products (VMWare, Xen, etc). The "real hardware" is a "DMA re-map" unit that Milligan likened to "an MMU (memory management unit) for DMA." He said, "VT-d totally isolates each guest OS, even when accessing DMA with native device drivers."
Virtual I/O vs. "Direct assigned" I/O with VT-d(Source: Intel)Milligan added, "Without VT-d, we have ways of isolating guest OSes, but it's not as high-performing. VTD brings complete isolation at DMA level, and VLX provides it at the normal memory level. So each OS is using its native device driver, and accessing what it thinks is the physical hardware."Milligan said that other Intel Architecture virtualization products present guest OSes with emulated hardware, an approach that simplifies guest OS installation, at the cost of reduced performance and configurability. "We think of [enterprise virtualization] as an adjacent market. It's been helpful in educating the market. But wherever there's a real-time need, that's the kind of thing we're good at -- real-time determinism and predictability."