(1) (Virtualization Technology) The virtual machine capability in Intel's CPU chips. The VT circuits added virtual machine instructions to the x86 and Itanium families of CPUs. Introduced in 2004, the specific names are VT-x for the x86 and VT-i for the Itanium. The VT circuits in the CPU eliminate the need to paravirtualize (modify) the guest operating system to achieve maximum performance.
VT enables the virtual machine monitor (VMM) to run at the most privileged level, and it accelerates transitions between the VMM and guest OS. It traps the calls to the hardware from the guest operating system, saves the CPU state and restores it after the VMM handles the event.
VT for Directed I/O (VT-d)
Introduced in 2008, VT for Directed I/O (VT-d) enables direct memory access (DMA) transfers between devices and guest OS memory without using the VMM as an interim stage. This allows network and display adapters to be assigned to specific virtual machines for increased performance. For example, a second display adapter can be assigned to a VM running a CAD application, which must address the hardware directly, or a second network adapter can be assigned to a VM running a high-priority network application. See virtual machine and hardware virtualization.
(2) See Video Toaster.
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