Consolidating services onto fewer machines is appealing because they are easier to manage, and you can put that unused capacity you already paid for to work. Or, when you buy new gear, get a single high-quality machine with redundant hot-swap server-quality everything, instead of a gaggle of lesser boxes.

Virtualization isn't a new idea; IBM's VM operating system has been hanging around since the early 70s, and today a single zSeries mainframe runs thousands of concurrent Linuxes. (Remember the famous IBM commercial, "The Heist"? That's what that was about.) Of course IBM wants you to blow a million clams on their stuff, but virtualization works just fine on lower-end systems too.

The basic concept in all virtualization technologies is sandboxing. Applications and operating systems run in discrete environments, completely protected from each other, and strictly limited in how many system resources they can consume. That's the theory, anyway. It's like having a whole bunch of computers in one, and they can interact with each other just like a physical herd of computers. It's a great development and testing environment, a test-lab-in-a-box. You can test networking, cross-platform applications, multiple Web browsers, and clustering. Use it for secure shared Web hosting, provide multiple secure user environments for shared PCs, and safely give them root accounts. The latter is especially useful for companies that have continual streams of perma-temps rotating through.

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