Citrix desktop virtualisation customers are still using the VMware server hypervisor on the back end, but a Citrix executive claims a shift away from VMware is afoot.

Citrix is widely acknowledged as a major player in the desktop virtualisation market, but faces an interesting competitive challenge in that many or most Citrix XenDesktop customers are using technology from rival VMware on the back end.

Recently, Burton Group analyst Chris Wolf said most Burton Group clients that have deployed Citrix's virtual desktop infrastructure are still using VMware ESX servers to host the desktops. That's primarily because VMware offers a memory overcommit feature that allows greater density and consolidation levels, he said.

Citrix's John Humphreys, senior director of marketing for virtualisation and management, acknowledged this problem in an interview Wednesday, but said the trend is shifting.

"A year ago, about 90% of our sales of XenDesktop were hosted on VMware [servers]," Humphreys said. "Through the second or third quarter, that percentage is down around 60% to 70%."

That proportion is even lower with Citrix's latest round of sales. In the most recent customer engagements, only about 40% to 50% of new XenDesktop customers are using VMware on the back end, according to Humphreys.

Citrix maintains an agnostic approach that lets customers use any server hypervisor on the back end, Humphreys notes. Still, Citrix would prefer that customers use the XenServer hypervisor to host virtual desktops, and is planning upgrades to make that option more appealing.

Future versions of XenServer will optimise use of memory, and work more closely with Citrix's HDX technology to provide a better user experience, Humphreys said. Citrix also offers its basic hypervisor for free, a tactic aimed at getting XenServer into as many organizations as possible.

Humphreys acknowledged that VMware has a large install base for its server virtualisation technology, but said it's not a one-horse race. Just as businesses use numerous operating systems, customers are often choosing to use multiple hypervisors, he said.

Humphreys discussed several other desktop virtualisation topics this week, giving a preview of Citrix's plans for 2010.

In May of this year, Citrix unveiled Receiver for iPhone, a lightweight software client that lets IT shops deliver virtual desktops and applications to the iPhone. In December, Citrix plans to make Receiver available for the BlackBerry, and will do the same for Android-based smartphones early next year, Humphreys said.

Citrix is also working on XenClient, a bare-metal desktop hypervisor that will let users run multiple operating systems in complete isolation from one another. XenClient will go into beta in early 2010 and be available in the middle of the year, Citrix said.

Fueled partly by Windows 7, desktop virtualisation is on the verge of taking off with IT customers, Citrix believes. Already, Citrix is seeing many virtual desktop deployments of several thousand seats.

"The last few years, most organisations have been sitting on their hands when it comes to upgrading their desktop operating environment," Humphreys said. "They've taken a 'let's keep XP around as long as possible' approach."

But Citrix is betting that companies will switch from physical to virtual desktops at the same time they upgrade to Windows 7.

"We feel like Microsoft has gotten it right with Windows 7," Humphreys said. "It's a much faster, sleeker and more robust operating environment."