Software Developer FAQ: Intel® Virtualization Technology

by Geoff Koch

FAQ Basics

Frequently asked questions about the Intel® Virtualization Technology. Includes forums for developers to discuss and learn about these processors.

Ask software-related virtualization questions directly in the Virtualization & Software Development Forum or click here to contact the Intel® Software Support Team.

Why isn’t my question answered in this FAQ?
This FAQ attempts to highlight a subset of the publicly available information about virtualization at and other Web sites. It is not intended to be a comprehensive guide to all virtualization-related material that Intel has published. See the next item for tips on finding answers elsewhere. If you’d like to suggest a question and answer for inclusion in an updated version of this FAQ, please post your question in the Intel® Developer Zone Forums. By posting in the forums, you benefit from the knowledge of many people while the community benefits from the discussion.

I didn’t find the answer to my question in this FAQ. Where should I look next?
Start by searching It’s possible to search the subset of the site relating to software development by using the advanced search. Another option is searching the Intel Developer Zone site using Google. To do this, add “” to a Google search. Next, search the Intel Developer Zone Forums. The search box is at the bottom of the page. If the question hasn’t been answered, post it in the appropriate forum or contact the Intel® Developer Zone Support Team.

How do I report a change in the status of an FAQ item?
As platforms with Intel® Virtualization Technology enter the market and more advanced virtualization solutions become available, this FAQ will become dated or obsolete. If you believe that an item is no longer valid or in need of updating, please contact the Intel® Developer Zone support team. The entire developer community appreciates your assistance in keeping this FAQ current.

Where should I post or send questions that are not related to Intel Virtualization Technology?
Intel Developer Zone Forums offer a place for public questions and answers on Intel Software Development Products, Intel® platforms and technologies, and other topics. Intel engineers participate and provide answers in the forums. Another option is to contact the Intel® Developer Zone support team. If your question is about performance of an existing software-only virtualization solution on an Intel platform, your best bet is to contact the solution vendor director. Microsoft*, VMware*, and Citrix XenServer*, all maintain community Web sites with discussion boards and other information.

Intel Virtualization Technology is a set of hardware enhancements to client and server platforms that can help improve virtualization solutions on appropriately configured systems. Benefits include improvements in corporate client manageability and flexibility for server consolidation or legacy migration. Intel Virtualization Technology also is part of a collection of Intel silicon technologies that are expected to deliver new computing benefits for home and business users, and IT managers. The company refers to these technologies – which also include Hyper-Threading TechnologyIntel® Extended Memory 64 TechnologyIntel® Active Management Technology and LaGrande Technology (Intel® Trusted Execution Technology) – as the “Ts.”

Is Intel Virtualization Technology the same thing as Vanderpool Technology?
Yes. At the Spring 2005 Intel® Developer Forum in San Francisco, Intel announced the formal marketing name – Intel Virtualization Technology. This name now replaces the former code name “Vanderpool Technology.”

When will Intel Virtualization Technology be in the marketplace?
Intel platforms supporting Intel Virtualization Technology will ship in 2005 for desktop and Intel® Itanium® processor-based servers. The technology is expected in 2006 for mobile platforms and Intel® Xeon® processor-based servers and workstations. In January 2005, the company released the technology specifications to facilitate industry design collaborations and speed up advancements in virtualization.

Is Intel Virtualization Technology the same for IA-32 and Intel Itanium Architectures?
No. The implementation is different for many reasons, including the fundamental differences between the IA-32 and Itanium architectures. The IA-32 version of Intel Virtualization Technology is referred to as VT-x, and documentation on VT-x can be found on the Intel® Virtualization Technology web site. The Intel Itanium architecture version is referred to as VT-i, and documentation on VT-i can be found in Intel Virtualization Technology Specification for the Intel Itanium Architecture (VT-i) [PDF].

Collaborating* on optimization of VMware server and desktop products for Intel Virtualization Technology. Intel has a history of working with VMware on virtualization solutions.

What does Microsoft say about Intel Virtualization Technology?
Microsoft is building* virtualization capabilities into the Windows* platform via Windows hypervisor technology. Microsoft says this technology will be available in the next product wave of the Windows operating system, code-named Windows “Longhorn.” Hypervisor is a technology that will be integrated into the Windows operating system, providing customers with a high-performance virtualization solution for Windows and heterogeneous environments. Microsoft Windows hypervisor technology will support enhanced hardware technologies, such as Intel Virtualization Technology.

Does Xen support Intel Virtualization Technology? And what is Intel’s relationship with Xen?
Citrix XenServer* is incorporating* certain technology contributions from Intel into release 3.0 of the Xen hypervisor – an open source virtualization application that allows multiple operating systems to run concurrently on the same physical server. Intel has contributed code to the Xen project to enable support for Intel Virtualization Technology. Intel has supported the development of Xen since its origins as a University research project at Cambridge and the company continues to fund research and ongoing development of Xen.

Essential Concepts

What is Intel Virtualization Technology?

Virtualization Generally

What problem does virtualization address?
Cost. A typical IT organization can spend up 80 percent of its budget simply managing existing systems and applications.1 In the past, to simplify deployment and reduce potential software conflicts, IT organizations would often host just one application per server. This led to large numbers of underutilized servers. There are 150 times more servers today compared to a decade ago and these servers are 10 times more powerful. Virtualization helps to take advantage of this extra power by consolidating multiple applications and operating systems onto a single platform, thus increasing server utilization and reducing management, power and cooling requirements. Virtualization also allows for flexible allocation of resources to handle unexpected workloads.

At a high level, how does virtualization work?
In general terms, virtualization abstracts software from the underlying hardware infrastructure. In effect, it cuts the link that ties a specific software stack to a partic ular server. Virtualization allows platform resources-such as processing power, memory, I/O and storage-to be allocated and prioritized as needed based on business and application requirements. This is important since applications may have very different workload requirements. Flexible resource allocation can improve performance, increase consolidation ratios, and deliver better value for new platform purchases.

What are the software-related benefits of virtualization?
First, virtualization provides logical isolation between virtual partitions, so a software fault in one partition is unlikely to impact an application in another partition. And virtual partitions can be configured to provide automatic fail-over for one or more applications. Next, different security settings can be implemented for each virtual machine, allowing IT organizations to maintain a high level of control over end-user and administrative privileges. Third, virtualization simplifies the migration of legacy applications onto new platforms; instead of migrating the application onto a new operating system, it can be hosted with the existing operating system in a virtual partition on the new platform, with no need for software modification. Finally, virtualization streamlines test and development because successive iterations of the software stack, including the production version, can be hosted in separate virtual partitions on the same platform. In some cases, virtualization may allow IT organizations to test new and upgrade solutions on existing production platforms, without disrupting the production environment.

1 Based on a quote by Kevin Rollins, President and COO, Dell Corporation, as reported in Dell and Sun Offer Different Visions,, by Larry Greenemeier, September 17, 2003.

Virtualization on Intel Platforms - Software only and Hardware-Assisted

Aren’t there software-only virtualization products today that run on Intel platforms?
Yes. Virtualization software is available today from VMware, Microsoft and other vendors, providing Intel architecture-based servers with capabilities that were previously available only on mainframes. Many businesses are achieving 20-to-1 or even 30-to-1 consolidation ratios by moving legacy applications onto 4-way to 16-way Intel processor-based platforms, Intel reports. To create virtual partitions in a server, these virtualization products generate a thin software layer called the Virtual Machine Monitor (VMM) that runs directly on the server hardware. One or more guest OSs and application stacks can then be loaded on top of the VMM.

So then, what challenge is Intel Virtualization Technology trying to address?
In current IA-32 architecture, all software runs in one of four “privilege levels” or “rings” (Ring-0 through Ring-3). The OS traditionally runs in Ring-0, which affords privileged access to the widest range of processor and platform resources. Individual applications usually run in Ring-3, which restricts certain functions (such as memory mapping) that might impact other applications. In this way, the OS retains control to ensure smooth operation. Since the VMM must have privileged control of platform resources, the usual solution is to run the VMM in Ring-0, and guest OSs in Ring-1 or Ring-3. However, today’s OSs have been specifically designed to run in Ring-0. This creates certain challenges. In particular, there are 17 “privileged” instructions that control critical platform resources. These instructions are used occasionally in most existing OS versions. When an OS is not running in Ring-0, any one of these instructions can create a conflict, causing either a system fault or a wrong response.

What’s the workaround today when conflicts arise between an OS and VMM?
One workaround is runtime modification of the guest OS. In this case, the VMM monitors operation during runtime, and takes control of the processor whenever one of the 17 privileged instructions (see above) arises in a guest OS. The VMM manages the conflict, then returns control to the guest OS. Another is static modification of the guest OS, or paravirtualization. In this case, the guest OS is modified prior to runtime. Both these approaches have drawbacks. Runtime modification forces the VMM to provide complex workarounds during operation, which can impact performance. Paravirtualization prevents the VMM from hosting unmodified (legacy) guest OSs. Both approaches require extensive software development efforts from the VMM vendor, the OS vendor, or both. They also require that VMM and OS software be upgraded in tandem, which increases the cost and complexity of IT support.

How does Intel Virtualization Technology eliminate the gaps in current virtualization solutions?
Three ways. First, the technology provides a new, higher privilege ring for the VMM. This allows guest OSs and applications to run in the rings they were designed for, while ensuring the VMM has privileged control over platform resources. It eliminates many potential conflicts, simplifies VMM requirements, and improves compatibility with unmodified legacy OSs. Second, handoffs between the VMM and guest OSs are supported in hardware. This reduces the need for complex, compute-intensive software transitions. Third, processor state information is retained for the VMM and for each guest OS in dedicated address spaces. This helps to accelerate transitions and ensure the integrity of the process.

How will software vendors and IT organizations benefit from Intel Virtualization Technology?
A key goal of Intel Virtualization Technology is to make VMM software independent of OS software. This will free VMM vendors from the resource-intensive task of adapting their code in response to OS patches and upgrades. It will also make it easier for existing solutions to take advantage of the latest platform capabilities, with less need for VMM development and tuning. Other benefits include reduced cost and risk for IT organizations and enhanced security.

Industry Support for Intel Virtualization Technology

What does VMware say about Intel Virtualization Technology?
“With Intel VT, Intel delivered a robust virtualization infrastructure that complements VMware’s long–standing leadership in delivering high–performance virtualization products for Intel architecture,” said VMware President Diane Greene at IDF 2006. “Now with the Virtualization Technology for Directed I/O specification, which is the result of the long–term collaboration between VMware and Intel, we are building on that foundation.”

At the same conference, Intel Senior Vice President, Pat Gelsinger, said “Intel has led the industry in the specification, development and productization of hardware–assisted virtualization, and Intel VT is backed by broad ecosystem support, which is essential for customers to successfully implement this technology. With support for Intel VT across its virtualization product line, VMware customers can realize the incremental benefits of hardware–assisted virtualization. Today’s announcements enable acceleration of the mainstream adoption of virtualization occurring in the data center.”

Why is does Industry need Intel Virtualization?
Industry will continue to adopt virtualization for many reasons: collections of inefficient servers can be replaced with fewer machines; software can be tested while isolated in harmless virtual partitions; and data centers can gracefully (and virtually) conform to shifting work models, new technologies and changing corporate priorities.

Intel Resources

Where can I get free software-oriented information on Intel Virtualization Technology or virtualization generally?
The Technology & Research section of maintains a Web page on Intel Virtualization Technology with links to the detailed technology specifications (written for software developers) and a white paper (the source of much of the information in this FAQ). Other information is available at the Intel Developer Zone Virtualization Developer Community, which provides technical articles and code samples; strategic articles by Intel executives and other industry luminaries; Web-based training sessions and listings of face-to-face courses and webcasts; software products for evaluation and purchase; SDKs, and tools; and community forum discussions with experts and peers on development products, platforms, and technologies. Registration for the Intel Developer Zone is free and provides access to technical content and a newsletter.

I’m willing to pay. What other support or access can I get?
Intel® Software Partner Home provides next generation software development platforms, software development products and complementary marketing programs. Contact Intel® Developer Zone Support to find out when platforms with Intel Virtualization Technology will be available via the Intel Software Partner Program. By joining the Intel Software Partner Program (or buying Intel® Software Development Products), developers are eligible for Intel Premier Support, which provides advanced and personalized troubleshooting and support by e-mail.

About the Author

Geoff Koch is a science and technology journalist in Lansing, Mich. His articles on writing code for cellular or handheld devices include Culture: The Next Big Thing in Code and One Plea for More Open Cell Phone Platforms.



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