Microsoft has delayed until early 2007 an update for Microsoft Virtual Server, a technology that lets a computer run multiple incarnations of Windows simultaneously.

The SP1 (Service Pack 1) update to Virtual Server 2005 R2 will include support for two chip features, Intel's Virtualization and Advanced Micro Devices' Virtualization, that ease the task. Previously it had been scheduled to arrive in the fourth quarter, but a Microsoft representative confirmed the slip on Tuesday.

The postponement comes on the heels of Microsoft's delays of Windows Vista and Office 2007. "Quality always takes priority over timeline," the Microsoft representative said.

Microsoft's top competitors have suffered similar setbacks. Market leader VMware had planned to release its next top-end ESX Server product, version 3.0, by the end of March but gave itself three more months. The other major competitor, the open-source Xen project, had planned to release its version 3.0 by August 2005 but in fact didn't release it until December.

Virtualization, which can let one machine replace several, is a hot topic in the computing industry as administrators try to get computers to do more work without consuming more power. It's hitting the mainstream, in particular as x86 processors make it easier to design and use.

The beta version of SP1 still is scheduled to arrive in the second quarter, said James Ni, group product manager for server virtualization at Microsoft.

The new version also will include Volume Shadow Services, which lets all a computer's virtual machines be backed up simultaneously, Ni said. The feature also permits the graceful restart of all those virtual machines, letting customers rely on the software without having to worry as much about the consequences of server failure.

"Basically, it allows us to do a snapshot of all the virtual machines running on a host. Then you can use something like Virtual Server with Data Protection Manager to create good backup and recovery," Ni said. "You can recover the entire host and all the virtual machines running in a very orchestrated fashion."

Microsoft faces major competition in the market from EMC subsidiary VMware and increasingly the Xen project that's being built into forthcoming versions of Suse Linux Enterprise Server and Red Hat Enterprise Linux.

Microsoft is working hard for a piece of the action, however. In December, it cut prices of Virtual Server 2005 R2 from $999 to $199 for the Enterprise Edition and $499 to $99 for the Standard Edition. The Standard Edition runs on servers with up to four processors, while Enterprise is for larger machines.

At the same time, though, market leader VMware is making its own moves. It released its Player software for free, which lets people download and try out virtual machines preconfigured with software, and made its GSX Server product into the free VMware Server. That product competes directly with Microsoft Virtual Server; VMware still charges for its higher-end ESX Server.

Much of Microsoft's attention is directed toward the future with a successor, the Microsoft hypervisor, code-named Viridian. Virtual Server requires Windows as a foundation, but hypervisors are lower-level software. ESX Server and Xen both employ the hypervisor approach.

One major change coming with Viridian will be support for 64-bit virtual machines, Ni said. That will catch Microsoft up with Xen and VMware, which support 64-bit virtual machines today.

Viridian isn't likely to debut until 2008 at the earliest, however. It's designed to work with the upcoming Longhorn Server, a server-oriented version of Windows Vista that's scheduled to arrive in 2007, but it's more likely to arrive with a service pack sometime 18 to 24 months afterward, Ni said.

"We're not committing to whether the hypervisor is part of the initial release or not. Right now, from a scheduling perspective, it doesn't look like it," Ni said.