In computing, hardware-assisted virtualization is a platform virtualization approach that enables efficient full virtualization using help from hardware capabilities, primarily from the host processors. Full virtualization is used to simulate a complete hardware environment, or virtual machine, in which an unmodified guest operating system (using the same instruction set as the host machine) effectively executes in complete isolation. Hardware-assisted virtualization was added to x86 processors (Intel VT-x or AMD-V) in 2005 and 2006 (respectively).
Hardware-assisted virtualization is also known as accelerated virtualization; Xen calls it hardware virtual machine (HVM), and Virtual Iron calls it native virtualization.
Hardware-assisted virtualization reduces the maintenance overhead of paravirtualization as it reduces (ideally, eliminates) the changes needed in the guest operating system. It is also considerably easier to obtain better performance. A practical benefit of hardware-assisted virtualization has been cited by VMware engineers and Virtual Iron.
Hardware-assisted virtualization requires explicit support in the host CPU, which is not available on all x86/x86_64 processors.
A “pure” hardware-assisted virtualization approach, using entirely unmodified guest operating systems, involves many VM traps, and thus high CPU overheads, limiting scalability and the efficiency of server consolidation. This performance hit can be mitigated by the use of paravirtualized drivers; the combination has been called “hybrid virtualization”.
In 2006 first-generation 32-bit and 64-bit x86 hardware support was found rarely to offer performance advantages over software virtualization.