popular for Web site hosting. SWsoft's Virtuozzo, based on the open-source OpenVZ project, employs this approach, while Sun Microsystems' Solaris built the technology into its Solaris 10 operating system. Microsoft has said it's considering a similar move for Windows.
Useful technology, lots of buying options--sounds swell. Why doesn't everybody do this?
Mainly because it's new to most people. Also, it can hurt performance as virtualization software intercepts communications between hardware and software, and to use it, computers need more network capacity and more memory. Virtualization also adds a new level of complexity, and administrators must test it with their hardware and software.
It doesn't sound so complex to me. Software just runs in a different compartment, right?
Consider some of the repercussions of unshackling software from its hardware. Much server software is priced on the basis of how many processors a server has. What happens when, through virtualization, you're running a particular application on two of a computer's four processors? Then what happens when you boost the virtual machine size to three processors? And how about moving that virtual machine over to a different system altogether? The software industry has only begun adapting to the new reality.
Here's another wrinkle: some software, during installation, records what amounts to the hardware fingerprints of the computer it's running on to counter piracy, while other packages require a hardware "dongle" to be attached. So there are serious constraints to shuttling virtual machines around with abandon.
OK, now I'm intimidated. Is this just a fad that I can wait out?
If you're a server administrator, you probably can't and shouldn't avoid virtualization forever. Xen now is built into both major commercial versions of Linux--Novell's Suse Linux Enterprise Server and Red Hat Enterprise Linux. And Intel and AMD are racing to build virtualization into their chips. Newer processors from both companies have hardware support for some virtualization tasks, making it possible to run Windows on Xen, for example. Future features will improve performance of memory access. Virtualization on the PC, though, isn't likely to catch on widely anytime soon.
What can I do with virtualization on a PC?
Software from Parallels will let Mac users run Windows on the newer Intel-based machines. VMware is working on its own software, called Fusion, to accomplish the same end. That can be handy when Mac users need to fit in better with a Windows-dominated world. For Windows users, VMware's player software can be used to try out Linux, run older software on a newer system, and isolate personal and work tasks. Intel thinks administrators will like to run their own management software in a separate virtual machine, letting them fix worm-infested PCs remotely. Developers get the ability to debug programs in virtual machines that can simulate diverse combinations of software and that don't corrupt hard disk data if they crash. For administrators, another nice PC virtualization technology involves replacing a standalone system and running virtual PCs on central servers to cut energy and maintenance costs.
VMware offers free versions of its software, but there are other fees. To run Windows on a Mac, you need a full--not upgrade--version of the operating system. And with Vista, the restrictions get even tighter: only the pricier Ultimate and Business versions are permitted. Businesses with a volume license agreement with Microsoft may run up to four instances of Windows Vista Enterprise on a single PC, but others must pay for each copy.
What are the server costs?
Xen is built into Red Hat Enterprise Linux and Suse Linux Enterprise Server at no extra cost beyond the support subscriptions. Novell customers may run as many SLES virtual machines as they want on a single computer for one support subscription. Red Hat prices similarly with its RHEL Advanced Platform version, but imposes a four-virtual machine limit for its basic RHEL Server version.
VMware's prices have come down. For example, its former GSX Server product became the free VMware Server product. But there still are significant fees. For a two-processor machine, ESX server and higher-level components that make up the company's Virtual Infrastructure 3 product cost a minimum of US$1,675 for a dual-processor server, including support and subscription costs. The fuller-featured Enterprise version of that product costs US$6,957 for the same hardware. Doubling a server's processor count doubles the price. It sounds steep, but it's still likely to be less expensive than buying a new server or three.
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