Citrix Systems is a strategic investor in Virtual Computer, a startup that has just released as beta software its NxTop bare-metal hypervisor for desktops.

Citrix announced earlier this month that it planned to bring out in the second half of 2009 a bare-metal, client-side hypervisor that would synchronize its operations with Citrix's XenServer hypervisor. Citrix officials weren't immediately available to say whether they are watching development of Virtual Computer's product line or have already decided to use it.

The phrase "bare metal" means the hypervisor sits close to the computer processor underneath the operating system and passes instructions directly to it. An earlier generation of hypervisors sat above the operating system and passed processing requirements of virtual machines through it to the CPU.

In today's announcement, Virtual Computer president and CEO Dan McCall said the Westford, Mass., company received $15 million in its second round of venture capital funding, after previously receiving $6 million. The software startup was founded in November 2007.

Two firms, Highland Capital Partners and Flybridge Capital Partners, were the lead investors, with Citrix added as a "strategic investor." Startups often opt for a strategic investor for the implied endorsement of their technology by a market leader. The amounts invested by each were not announced, as is customary in such combinations.

"Not only did our current investors show their continued support for the company, but we were able to add a proven leader in the virtualization market as a strategic investor," said McCall.

In the announcement, Citrix officials suggested there was a link between Virtual Computer and Citrix's recent announcement of "Project Independence," its plan to offer desktop virtualization that allows a mobile worker to disconnect from a virtualization host and continue working on a desktop running its own hypervisor. In 2007, Citrix acquired XenSource, the company that commercialized the Xen open source hypervisor. Virtual Computer also uses Xen as the basis for its desktop life-cycle management products.

"We see great synergy between their use of Xen technology for PC lifecycle management and Project Independence. ... We look forward to working with Virtual Computer in a mutually beneficial capacity and see our investment as the first step in that direction," McCall said.

Citrix senior director of strategic development, Andy Cohen, clarified: "While Citrix does not have plans at this time to use the NxTop hypervisor, there is a great synergy between the investment and Project Independence."

The heavy venture capital investment in desktop virtualization runs counter to a trend of venture capital firms pulling back on investments in anything other than proven technologies.

Peter Bell, general partner in Highland Capital Partners, said in the announcement that desktop virtualization products from Virtual Computer will "deliver cost-saving benefits ... in any economic climate."

McCall was the co-founder of Guardent, a managed security services provider that was sold to VeriSign in 2004. McCall became VeriSign's VP of corporate development after the acquisition.

Co-founder and CTO of Virtual Computer is Alex Vasilevsky. He was a co-founder and CTO of Virtual Iron, a VM management company whose offerings are based on the Xen hypervisor.

The article was edited on 1/29 to clarify statements made by Citrix.