Virtualization technology has a long history in computer science. It was Christopher Strachey who first published a paper entitled "Time Sharing in Large Fast Computers" in the International Conference on Information Processing at UNESCO, New York, in June 1959, and he commented that his paper, "...was mainly about multi-programming (to avoid waiting for peripherals)." Virtualization today is a methodology whereby the resources of a computer are divided into multiple execution environments, by applying one or more technologies such as hardware and software partitioning, time-sharing, partial or complete machine simulation, emulation, or quality of service. This issue of the Intel Technology Journal (Volume 10, Issue 3) reviews virtualization, especially Intel^® Virtualization Technology (Intel^® VT). These seven technical papers describe the key capabilities of virtualization on Intel’s hardware and software platforms and the virtualization roadmap for both Intel^® Architecture and Intel^® Itanium^® processors. Intel VT is part of a collection of premier Intel designed and manufactured silicon technologies that deliver new and improved computing benefits for home and business users, and IT managers.

There are many advantages to virtualization. Virtual machines can be used to run multiple operating systems simultaneously—different versions, or even entirely different systems. These machines can also be used to consolidate the workloads of several under-utilized servers so that fewer machines are used, thereby saving hardware resources and reducing related infrastructure costs. Legacy software can run on virtual machines, whereas an older application might not run on newer hardware and/or operating systems. They can also provide secure, isolated sandboxes for running un-trusted applications, making virtualization an important concept in building secure computing platforms. To the user, they can provide the illusion of hardware, or hardware configuration (such as SCSI devices, multiple processors, etc.) and they can even be used to simulate networks of independent computers. Finally, in this age of heightened awareness regarding security of information, they enable powerful debugging and performance-monitoring scenarios and moreover make software easier to migrate, thus aiding application and system mobility.

The first two papers provide an overview of Intel VT architectures both for hardware and for directed I/O. The first paper provides an overview of Intel VT for the IA-32 Intel^® architecture and Intel VT for the Intel^® Itanium^® Architecture. The second paper looks at I/O-device virtualization known as Intel VT for Directed I/O. This paper surveys a variety of established and emerging techniques for I/O virtualization and outlines their associated advantages and challenges. The paper details the architecture of Intel VT for Directed I/O and describes how it enables the industry to meet the future challenges of I/O virtualization.

The third paper looks at Virtual Machine Monitors and Xen*, an open source virtual machine monitor (VMM) developed at the University of Cambridge to support operating systems that have been modified to run on top of the monitor. Intel has extended the Xen VMM to use Intel VT to support unmodified guest operating systems.

The fourth, fifth, and sixth papers look at new and extended usage models. The fourth paper looks at how Intel VT enables a virtualized environment for a host of provisioning manageability and diagnostic applications for the IT professional. One of the usage models involves embedded IT through the use of Intel VT for Client Isolation and Recovery (CIR) that emphasizes isolating manageability and security services. The fifth paper describes the unique requirements that embedded systems and communications infrastructure place on virtualized environments and shows how Intel is working with a number of third parties in the embedded markets. Some features of the embedded applications include maintaining bounded real-time performance; increased system uptime, and easier software migration—without having to bring down the application. The requirement for embedded applications dictates that different architectural and design tradeoffs be made within the VMM and the guest operating systems executing within the virtual machines. The sixth paper presents how an enterprise IT organization sees virtualization in the enterprise and how it can be applied. Enterprise virtualization programs can help to achieve higher server utilization, make it easier to manage data center assets, and reduce the consumption of datacenter resources (floor space, power, etc.), as well as facilitate simpler server releases.

The seventh and final paper looks at performance benchmarking for virtualization. There are no established performance methodologies to measure virtualization performance. The vConsolidate benchmark is presented as an example implementation, highlighting the compromises required in workload selection, component definition, and metric aggregation.

These papers highlight new and innovative virtualization markets, open standards support, and hardware platforms with efficient processor virtualization. Best of all, most PC users today, though they may not know it, are already using virtualization in their off-the-shelf systems that are based on Intel Architecture platforms.

Note: Throughout this journal, references to VT-x refer to Intel VT for the IA-32 Intel Architecture, VT-i refers to Intel VT for the Intel Itanium architecture, and VT-d refers to Intel VT for Directed I/O.