Microsoft last week said it has now sold 6.5 million licenses of its Microsoft Desktop Optimization Pack (MDOP) client-level virtualization software, more than double the total of 3 million licenses that it had sold as of January.

MDOP, which is available only to customers that have volume Windows licenses and Software Assurance maintenance contract, offers a variety of technologies supporting desktop virtualization and application streaming. The software can be used to run applications and store data for end users on servers, potentially making systems more secure and easier to manage.

Shanen Boettcher, Microsoft's general manager of Windows client product management for enterprise users, included the updated sales total for MDOP licenses in a post on the software vendor's Windows Vista blog. MDOP costs between US$7 and $10 per license annually, according to Boettcher.

Boettcher also said in the blog post that Microsoft has completed its acquisition of Kidaro Technologies, which sells technology designed to make the desktop virtualization experience more invisible to end users and easier for IT to manage. Kidaro's technology is scheduled to be incorporated into MDOP by the first half of next year, with the combination getting a new name: Microsoft Enterprise Desktop Virtualization.

Altogether, Boettcher said, Microsoft has invested more than US$400 million in developing MDOP and expanding it through acquisitions of virtualization vendors such as Kidaro and Softricity.

Microsoft competes with VMware as well as a number of start-up vendors in the desktop virtualization market. Unlike the server virtualization business, in which VMware has a substantial lead, the desktop part of the market remains "pretty wide open," Boettcher said in an interview. "Less than 1 per cent of desktops run some form of virtualization."

Microsoft hopes to win users by providing better virtualization management through its System Center tools and integration with its Active Directory technology.