For many years, virtualization was confined to proprietary mainframe systems. The ability to run multiple operating systems on the same physical platform was regarded as useful or feasible only in the largest server systems and there it remained—for decades. But the introduction of Intel® Virtualization Technology (Intel® VT), and the recent emergence of new virtualization solutions for Intel-based systems are changing all of that. We began our work on Intel VT with a simple premise: the ever-increasing performance of platforms based on Intel® Architecture (IA) would overcome the traditional performance barriers to full-system virtualization, and eventually bring the capability to all classes of systems from servers to clients to embedded systems. The ubiquity of the capability, in turn, would spur innovation in new uses for the technology. However, some barriers stood in the way of turning this opportunity into a reality: traditional IA wasn’t designed to allow straightforward sharing of processor or other platform resources, and so software needed to resort to complex work-arounds to make virtualization work. To get over these barriers, we set out to identify the various aspects of IA-based systems that complicate virtualization, and then we extended the hardware architecture to fix them. The result was Intel VT, a multi-generational series of extensions to Intel® processor and platform architecture that provides a new hardware foundation for virtualization, establishing a common infrastructure for all classes of IA-based systems. The broad availability of Intel VT makes possible entirely new applications for virtualization in servers, clients, and embedded systems, providing new ways to improve system reliability, manageability, security, and real-time quality of service. This issue of the Intel Technology Journal (ITJ), Volume 10, Issue 3, on virtualization begins with a look at Intel’s VT hardware roadmap, which is rooted in new support for virtualizing IA-32 and Intel® Itanium® processors, and extends into the platform with new support for I/O device virtualization. You’ll find papers that show how Intel VT hardware significantly simplifies the design and implementation of virtualization software, and how it provides a supportive new infrastructure for system and I/O-device vendors to build and extend virtualization solutions based on Intel® platforms. The success of any new hardware architecture is highly dependent on the system software that puts its new features to use. In the case of virtualization technology, that support comes from the virtual machine monitor (VMM), a layer of software that controls the underlying physical platform resources, sharing them between multiple "guest" operating systems. As the first to market with hardware support for IA-32 virtualization, Intel VT is already incorporated into most commercial and open-source VMMs including those from VMware, Microsoft, XenSource, Parallels, Virtual Iron, Jaluna and TenAsys. Throughout this issue of the ITJ you’ll see how Intel VT hardware is being used by VMM developers, from the open-source Xen* VMM, to a lightweight VMM design in support of client manageability, to enhanced embedded real-time system design. The traditional use of virtualization in mainframe systems has been to simplify the provisioning and management of the physical resources of large server systems. But as virtualization technology becomes widespread in IA-based systems, the computing industry is witnessing a remarkable proliferation of new uses for virtualization, and a reinterpretation of old usages that extends well beyond the traditional mainframe. In this ITJ issue, you’ll find many such examples, including a case study of server consolidation in a modern datacenter by Intel’s Information Technology Group, improved client manageability and security enabled by Intel® vPro™ technology-based platforms with Intel VT support, and the marriage of real-time system design with virtualization to meet the needs of embedded and communications applications. A common theme throughout these case studies is that different usage models and market segments require different styles of VMM software design—but all share a need for the improved platform hardware support for virtualization. It’s gratifying to see that our original vision for Intel VT of providing broadly available hardware support to enable innovative new applications of virtualization is indeed becoming a reality. I hope that you enjoy this special ITJ issue on virtualization and the in-depth view that it provides into Intel’s plans to support this emerging trend in IA-based systems, and the vibrant ecosystem that is forming around Intel VT. | 
