Microsoft stunned LinuxWorld attendees last week by pledging to support Linux virtual machines on its Virtual Server and revealing free virtual machine additions for Red Hat Linux and Novell SUSE Linux. It wasn't the only dogs-playing-with-cats kind of moment last week: Apple offered up software to let Windows run on Intel-based Macs.

What's going on here? The answer is virtualization, the ability to much more easily carve up servers and PCs into compartments that can run multiple applications under different operating systems at the same time. Business interest in virtualization--particularly of servers--is picking up quickly, and vendors are racing to stake out this emerging market. The result could blur some of the hard-and-fast lines drawn between operating systems.

The appeal can be seen at RSA Security, where software engineers used to run from room to room setting up different server hardware, application, and operating system combinations to test new security products. Today, a developer tells the data center which environments are needed, and they're created as virtual machines that can run different apps on Windows or Linux, using the same server hardware, says RSA engineering director Roy Rezac. Two or more developers' virtual machines may even run simultaneously on one pizza-box-sized, rack-mounted server. Businesses see that flexibility lowering costs, improving load balancing, and increasing server utilization and consolidation.

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"There are hardware savings, but to me that's not important," Rezac says. "The real savings is in making developers 5% to 10% more productive."

Microsoft's support for an operating system that rivals its lifeblood Windows is the most surprising development. In the past, it was possible to run Linux machines under Windows, but companies were on their own if problems arose. Support of Linux virtual machines running under Windows is a sign that Microsoft recognizes it's a heterogeneous world--companies, especially big ones, aren't all Windows. But it's also a defensive play to keep from losing the virtualization market to VMware or open source options as Microsoft tries to get its act together.

Apple's release last week of its Boot Camp downloadable software to run Windows on the Mac had Mac zealots buzzing, but the business value likely will be limited. The big deal for business IT is the developments in the server virtualization arena.

Intel and Red Hat last week unveiled a program to provide customers with tools and access to data centers to help them plan, develop, and test Linux systems, with a particular emphasis on virtualization pilot projects. The program should make it easier to create virtual servers with Linux--and help Red Hat compete with Microsoft's Virtual Server.

Microsoft also said it's making Virtual Server 2005 R2 available as a free download, a way to keep from losing market momentum after the delay of Virtual Server 2005 Service Pack 1, now expected sometime next year. Microsoft also licensed its Virtual Hard Disk format to XenSource, the company formed to develop products on top of the open source Xen virtualization software. In the first three days the Linux add-ins to Microsoft Virtual Server were available, they were downloaded 70,000 times.

Under Pressure
Microsoft's hand may have been forced. VMware, the EMC-owned market leader in virtualization software, started giving away VMware Server in February. VMware Server allows Windows or Linux to be hosted on an x86 server under Windows or any other operating system. The Xen 3.0 open source software takes advantage of virtualization hooks planted in the newest Intel and Advanced Micro Devices chips to enable the creation of a Windows or Linux virtual machine--or both--on the latest generation of x86 servers. Virtual Iron Software said last week it's abandoning its proprietary hypervisor and basing the 3.0 version of its policy-based management software for virtual machines on Xen.

Virtual server management will be one problem for IT managers. XenSource had planned to develop extensive Xen-based management products for virtual machines, but it recently backed off, launching a more limited XenEnterprise. "Customers told us they were more inclined to purchase systems management tools from IBM, HP, and BMC Software," XenSource CTO Simon Crosby says.

Microsoft also wants its name on that list, as it expands its Systems Center tools. Companies "want the same tools to manage their virtual environments as are managing their physical ones" in the data center, says Jim Ni, group product manager for Windows Server marketing. To do so, Microsoft must produce its own hypervisor, virtualization software that functions like a microkernel operating system on top of a microprocessor, interpreting a Windows or Linux instruction from a virtual machine into the compiled language the chip can understand.

Both VMware's ESX Server and Xen 3.0 are hypervisors, which speed virtual machine performance by taking advantage of hardware assists built into Intel and AMD chips. Count on VMware to make the most of its lead and make it easier to generate and manage groups of virtual machines for any of the major x86 operating systems, including Windows, Linux, and Sun's Solaris 10 for x86. Microsoft plans to produce a hypervisor inside the upcoming Windows Longhorn server, scheduled for 2007, Ni says.

That lag, and Microsoft's history, may work against it in luring customers that want to run Linux virtual machines. "Microsoft is going to be very late to the game and will need to overcome a presumption that it will favor Windows," says Gordon Haff, virtualization analyst at Illuminata.