Microsoft Thursday did something it rarely does. The company released a beta for a long-awaited technology -- in this case its Windows Server 2008 virtualization technology Hyper-V -- ahead of schedule.

Hyper-V, formerly code-named "Viridian," is now available for download from Microsoft's Web site and is ready to be used with the current x64 beta version of Windows Server 2008, which is also available online. The technology, called a hypervisor, is the underlying virtualization technology for the server release, which is a major update that's expected to be released on Feb. 27, 2008. A beta of Hyper-V originally was planned to be released on that date as well.

Virtualization, or the ability to use virtual machine technology to run multiple OSes on a physical server, is widely seen as a disruptive technology and is becoming increasingly important as companies seek to cut costs and consolidate hardware in their data centers and IT environments. Microsoft had originally intended to release Hyper-V as part of the original release of Windows Server 2008, but the technology was delayed and is now scheduled to be generally available 180 days, or about six months, after Windows Server 2008 ships. Hyper-V's released was delayed earlier this year because Microsoft opted to pull out some originally planned features.

Hyper-V takes advantage of virtualization-optimized microprocessors from Intel and AMD and is meant to help Microsoft compete with virtualization leader VMware, which already has hypervisor technology on the market. Hypervisors allow for cross-platform support so that servers can run multiple versions of different OSes -- such as Windows and Linux -- side by side on one piece of hardware.

Bill Hilf, general manager of Windows Server at Microsoft, said customers have been asking the company for a built-in virtualization technology that works directly within the Windows Server environment so that it's easy to manage and implement. By design, Hyper-V is set up as what Microsoft calls a "role" within Windows Server 2008, and can be turned on or off as a customer wishes, he said. Roles are a new feature of the forthcoming release of the OS that allow servers to be set up so only the role or roles a customer wants them to play in the IT environment -- such as e-mail server or application server -- will be turned on.

Mike Neil, general manager of virtualization at Microsoft, said Hyper-V is meant to make the virtualization market "a two-horse race" between Microsoft and VMware. However, with Hyper-V not scheduled to ship until the second half of next year, the company has a lot of ground to make up to topple VMware from its leadership position. And Microsoft also faces pressure in providing built-in OS virtualization from Linux leader Red Hat, which already has integrated cross-platform virtualization into Red Hat Enterprise Linux.

Windows Server 2008 eventually will be available in multiple editions and will be offered with and without Hyper-V. Microsoft also plans to release a product called Microsoft Hyper-V Server specifically as a virtualization host environment in the second half of 2008.

A correction was made to this article on Dec. 13, 2007.