Virtualization is a white-hot market, and for good reason. For one thing, it allows users to mix and match computers and operating systems, and that, among other things, creates the flexibility to easily support older applications. The virtual machines that are created have their own advantages as well. Virtual machines share hardware, but operate as separate, isolated systems -- each with its own configuration and each in its own "sandbox" -- so there are security benefits.

Virtual machines can enable easy backups, quick reinstalls of clean versions of operating systems and application software, or rollbacks to the state of a system at any point in time (prior to a virus infection, for instance, or a serious software incompatibility). Virtual machines allow the simultaneous operation of different operating systems or of multiple versions of the same operating system, such as Windows 2000, XP and Vista. They can even run multiple copies of the same operating system.

This last feature can be enormously beneficial for large organizations, since it essentially creates more computers without requiring IT to actually buy additional hardware -- or pay for maintenance of same. It is generally less expensive to beef up an existing server than it is to buy an entirely new server -- though the savings depend on how many virtual machines you want to create, of course. And on the low end, virtualization can be seen as a kind of competition for blade servers and cheap 1U boxes. In other words, customers can buy fewer but larger servers and use virtualization to partition them instead of buying more blades and small, cheap servers to accomplish the same thing.

Virtual machines can be considerably easier to manage, provision, partition, create, modify or eliminate than the equivalent physical machines. The ease of testing untrusted applications and tweaking performance (changing the system configuration to boost speed for specific kinds of uses) and just the general flexibility to do more things with the hardware you have make virtualization a key technology for the future.

One of the main differences, so far, between the virtualization markets in the Mac and PC worlds is that Mac virtualizers let you run other operating systems, primarily Windows, on Macs but don't let you run multiple versions of the native Mac OS. Your average user might not care, but for enterprise use, this is a big deal.