Microsoft has admitted being some years away from delivering virtualisation at the operating system level.

Jim Ni, a group product manager for Windows Server marketing, said in an interview with vnunet.com that the technology will be "a few years out" but declined to give a more precise timeframe.

"It is too early to say when we will have these technologies rolled out," said Ni, adding that virtualisation will not be part of Longhorn Server, the forthcoming version of Microsoft's server operating system.

"It is based on the customer feedback from our hardware virtualisation and application virtualisation. We will see when those scenarios need to be met. We've got a lot of them covered today with our solutions."

Operating system virtualisation is a technology placed between hardware virtualisation and application virtualisation, allowing users to create a certain level of separation between applications with a limited overhead in computational resources.

Hardware virtualisation allows a virtual system to operate as if it were running on a dedicated server, offering a high level of stability and security. The technology is available in Microsoft Virtual Server, VMware or the open source Xen software.

Application virtualisation makes individual applications available in a virtual way. The technology makes legacy applications available and is offered by Softricity, a company that Microsoft is in the process of acquiring.

Operating system virtualisation provides a cross-set of the other virtualisation technologies. While drivers and the operating system are shared, the technology allows for numerous instances of applications to run side by side.

The technology could be attractive for service providers seeking to run several web servers on a single system. One application crashing will not affect other applications, but a virus will still affect all software.

SWSoft's Virtuozzo currently offers operating level virtualisation for both Linux and Windows.

Sun Microsystems also offers operating system-level virtualisation for Solaris through its secure container functionality, and is currently beta testing a product that allows for Red Hat Linux virtualisation under Solaris.

Ni insisted that he does not feel pressured by this competition to speed up his development. "We have not seen widespread use of this technology," he said.

Customer demand is centred around Microsoft's IIS webserver and SQL Server database, he added. Microsoft already offers a technology to run multiple instances of SQL and will add that functionality in the forthcoming version of IIS.

"We have covered a lot of the major applications and usage cases for this," said Ni.