Microsoft's last minute decision not to ease virtualisation restrictions for Windows Vista is an "unjustified" attempt to "delay market adoption of competitive virtualisation software", analyst firm Gartner said in a new analysis. 

The software giant was planning to change the licensing terms for Vista Home Basic and Vista Home Premium, allowing users to run the software in a virtual compartment.

The changes would further ease virtualisation restrictions for Vista Ultimate and Vista Business, which currently lack support for the Bitlocker data encryption technology and have restrictions on digital rights management.

But Microsoft pulled the planned changes at the last minute without explanation.

Gartner claims that Microsoft is delaying the licensing changes because it wants to slow down the desktop virtualisation market. The firm currently lacks a competitive virtualisation product and is not expected to catch up until 2009.

"Microsoft has a strong motivation to delay," wrote Gartner fellows Brian Gammage and Neil MacDonald, and research vice president Michael Silver.

The enterprise market for running a virtual desktop is currently limited to application testing for developers and security researchers.

Apple users have jumped on desktop virtualisation as way to run Windows XP and ensure access to applications which are not available on the OS X platform.

But Gartner noted that lifting virtualisation restrictions could increase Vista sales from Mac users.

Enterprises could eventually use desktop virtualisation to create so-called portable clients, where a user's operating system, application and data are stored on a central server.

All the data would be transferred to a virtual compartment on the computer where the user logs in, but this is currently impossible because of the DRM and Bitlocker restrictions.

Microsoft offers free desktop virtualisation through its Virtual PC 2007, but the software is considered inferior to competing products from vendors such as VMware and SWSoft, maker of the Parallels software. 

Microsoft is also trailing behind its competitors in creating a virtualisation technology that relies on a hypervisor.

Instead of relying on a standalone virtualisation application such as Virtual PC 2007, hypervisor-based virtualisation is embedded into the main operating system which allows for better performance.

Microsoft has previously justified its virtualisation restrictions by arguing that virtualisation presents the user with security risks. The restrictions are intended to limit the technology to educated users and businesses.

Gartner dismissed these arguments as "overblown" and "fundamentally no different than those posed by consumers running Windows as 'administrators' today".

The analyst recommended that users looking for a virtual desktop use Windows XP, which has no restrictions in its licence.