Microsoft has loosened some of its licensing terms related to virtualization, allowing consumers who use Windows Vista Home Basic and Home Premium to run those OSes in a virtualised environment.

Customers with the Home and Home Premium editions of Vista can now run them as a guest operating system on a virtual machine, the company said. Among other things, that should mean that Apple Mac users who want to run Vista alongside the Mac OS can now do so without having to buy a more expensive version of Windows.

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The move is part of a new effort announced by Microsoft to become a bigger force in the market for virtualisation software, and step up its assault on established leaders such as VMware.

The plans announced on Monday include the acquisition of a start-up company, Calista Technologies, whose graphics technology is designed to improve the end-user experience for people who access their Windows desktop remotely from a server, Microsoft said. It also announced new licensing rates for corporate users, and extended its partnership with Citrix Systems to make Citrix's Xen virtualisation software work better with Microsoft's server and desktop software, it said.

Virtualisation technologies separate the software on a computer from its underlying hardware, allowing it to be deployed in more flexible ways. Virtualisation can allow multiple operating systems to run on one computer, for example, or allow application workloads to be shifted between computers more easily to improve hardware utilisation.

The technology has been around for decades but was popularised in server environments recently by VMware and others. More recently, Apple introduced virtualisation for its Mac desktops so that users can run both the Mac OS and Windows on the same machine.

Microsoft has not been a significant player in virtualisation, but it hopes to change that with its announcements this week. It plans to discuss the changes at its Virtualization Deployment Summit, a two-day event for 300 of its customers and partners that starts today.

It argued that the virtualisation market remains open for newer players like itself.

"Very few customers are able to reap the benefits of virtualisation today," Bob Muglia, senior vice present of Microsoft's Server and Tools Business, said. "We estimate that less than five percent of companies are utilising virtualization technology because it is simply too cost-prohibitive and complex."

Microsoft's strategy will be to offer a full range of virtualisation products, including desktop, server and management software, and do so at a competitive price, Muglia said.

For businesses, customers who subscribe to Microsoft's Software Assurance maintenance program can now get an annual subscription to Microsoft's desktop virtualization software for $23 (£12) per desktop, the company said.

Citrix is developing a software tool that will make it easier for customers to transfer virtual machines between Citrix XenServer and Windows Server 2008 Hyper-V. A test version of the tool will be available in the second quarter, and the final version will be released along with Hyper-V, Microsoft said.

The technology from Calista aims to improve the experience for people who access their Windows desktops remotely from a server. It allows people to view multimedia content on a PC or thin client without the media player or software codecs they would normally need installed.

Microsoft will add Calista's graphics technology to future virtualization products, it said. Calista, of San Jose, California, is now a Microsoft subsidiary.