Intel has launched two Pentium 4 CPUs – 672 and 662 – supporting the new Intel Virtualization Technology (VT). Formerly known as Vanderpool, this technology enables a CPU to act as if it were several CPUs working in parallel, in order to enable several operating systems to run at the same time in the same machine. In this tutorial we will explain everything you need to know about this new technology.

Virtualization technology is nothing new. There is some software on the market that enables virtualization and probably VMware is the most famous one. With this technique, a single CPU can act if it were several CPUs running in parallel, allowing the system to run several operating systems at the same time.

You may confuse virtualization with multitasking or even with Hyper-Threading. On multitasking, there is a single operating system and several programs running in parallel.  On virtualization, you can have several operating systems running in parallel, each one with several programs running. Each operating system runs on a ”virtual CPU“ or ”virtual machine“. And Hyper-Threading simulates two CPUs were there is just one physical CPU for balancing performance using SMP (Symmetric Multi Processing), and these two CPUs cannot be used separately.

Figure 1: Multitasking.

Figure 2: Hyper-Threading.

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Figure 3: Virtualization.

Of course if a CPU has both Hyper-Threading and Virtualization Technology each virtual CPU will appear to the operating system as if two CPUs are available on the system for symmetric multiprocessing.

If you pay close attention, Virtualization Technology uses the same idea of Virtual 8086 (V86) mode, which is available since 386’s. With V86 mode you can create several virtual 8086 machines to run DOS-based programs in parallel. With VT you can create several ”complete“ virtual machines to run full operating systems in parallel.

But if there are software like VMware that enables virtualization, why implement Virtualization Technology inside the CPU? The advantage is that CPUs with Virtualization Technology have some new instructions to control virtualization. With them, controlling software (called VMM, Virtual Machine Monitor) can be simpler, thus improving performance compared to software-only solutions.