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x86 virtualization is the method by which the x86 processor architecture is virtualized. Unfortunately, the x86 processor architecture did not originally meet the Popek and Goldberg virtualization requirements. As a result, it was very difficult to implement a general virtual machine on an x86 processor. Recent extensions to the x86 architecture have resolved this and other virtualization difficulties.

Software virtualization techniques

On February 8, 1999, VMware introduced the first x86 virtualization product, "VMware Virtual Platform", based on earlier research by its founders at Stanford University. VMware filed for a patent on their techniques in October 1998, which was granted as on May 28, 2002. VMware and similar virtualization software for the x86 must employ very sophisticated techniques to trap and virtualize the execution of certain instructions. These techniques incur some performance overhead as compared to a VM running on a natively virtualizable architecture such as the IBM System/370 or Motorola MC68020.

Kevin Lawton started the Plex86 project (originally called "freemware") to create a Free software for x86 virtualization. The focus of the project has since changed to support only Linux as a guest operating system, but prior to that Mr. Lawton published the paper Running multiple operating systems concurrently on an IA32 PC using virtualization techniques, which gives an analysis of what aspects of the x86 architecture are hard to virtualize and some techniques to overcome these difficulties.

Microsoft offers two Windows-based x86 virtualization products, Microsoft Virtual PC and Microsoft Virtual Server, based on technology they acquired from Connectix.

Recent research efforts have sought to provide high performance virtualization of x86 by presenting an interface to virtual machines that differs from that of the raw hardware. Operating systems are ported to run over this interface, which does not use the hard-to-virtualize parts of the x86 instruction set. This technique is known as paravirtualization. The research systems Denali, L4, and Xen employ this technique to run modified versions of various operating systems.

Hardware support in x86 processors

Intel and AMD have independently developed virtualization extensions to the x86 architecture. They are not directly compatible with each other, but serve largely the same functions. Either will allow a virtual machine hypervisor to run an unmodified guest operating system without incurring significant emulation performance penalties.

Intel's virtualization extension for 32-bit and 64-bit x86 architecture is named VT (short for Virtualization Technology), and is sometimes referred to by the code name "Vanderpool". Intel has also published specifications for Vanderpool for the IA-64 (Itanium) processors; formerly the IA-64 virtualization was code-named "Silvervale".

AMD's virtualization extension to the 64-bit x86 architecture is named AMD Virtualization, and is sometimes referred to by the code name "Pacifica".

Both Intel and AMD have contributed support for their virtualization extensions to the Xen virtual machine monitor, allowing it to execute unmodified guest operating systems.

Hardware availability of VT and AMD Virtualization

Intel VT was officially launched at the Intel Developer Forum Spring 2005. It is available on all Pentium 4 6x2, Pentium D 9xx, Xeon 7xxx and Core Duo processors, though in the latter case it is sometimes disabled in the BIOS/EFI.

AMD processors using Socket AM2, Socket S1, and Socket F include AMD Virtualization support. In May 2006, AMD introduced such versions of the Athlon 64 and Turion 64 processors. It is expected that Opteron processors with AMD Virtualization support will be announced in August 2006.

Virtualization software utilizing VT

The following software is known to conditionally make use of virtualization technology features:
  • Microsoft Virtual PC
  • Microsoft Virtual Server — a future version (Virtual Server 2005 R2 SP1, to be released in Q1 2007*) will support Intel VT and AMD Pacifica extensions.
  • Parallels Workstation — lightweight hypervisor with Intel VT-x support
  • TRANGO real-time embedded hypervisor
  • VMware — on Intel processors, VMware Workstation 5.5 requires Intel VT to execute 64-bit guests.*
  • Xen — Xen 3.0 uses Intel VT to execute unmodified guest operating systems.

See also

External links

General links
Hardware virtualization VT from Intel
Hardware virtualization Pacifica from AMD
Computer architecture | Virtualization software | X86 architecture

Virtuelle Maschine | Machine virtuelle (informatique) | macchina virtuale | virtuele machine | Maszyna wirtualna | Virtualization software | X86 architecture

Intel Virtualization Technology | Vanderpool | Vanderpool | Tecnologia de Virtualização da Intel

 

This article is licensed under the GNU Free Documentation License. It uses material from the "X86 virtualization".

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