The Excalibur Tech Preview provides a glimpse at several improvements to XenDesktop’s Desktop Agent designed to provide a great user experience with Windows 8 and Windows Server 2012 virtual desktops.

HDX technologies are important to the delivery of new generation Windows desktops and Windows 8 style apps because DirectX graphics technology has become the new norm. Excalibur offers a choice of software-based (CPU) rendering or hardware-based (GPU) rendering of Windows 8 desktops and DirectX 3D apps. (And don’t worry, OpenGL apps benefit, too.) Hardware rendering maximizes server scalability by offloading the CPU, although at the cost of more expensive server gear.

Windows 8 is especially well suited to mobile devices. So a lot of work is going into enabling Windows multi-touch support for future versions of the Citrix Receiver for iOS and Android. Our engineers have also succeeded in achieving a highly fluid desktop and application experience over mobile networks, even when bandwidth is limited. As discussed in detail in my blog post on Adaptive Display, the HDX SuperCodec has been enhanced in Excalibur with H.264-based Deep Compression from XenDesktop HDX 3D Pro that dynamically adjusts to changing network conditions.

GPUs also come into play as an option for H.264 encoding. Today’s GPUs aren’t limited to graphics rendering; they are high performance processing engines. Just as with graphics rendering, using a GPU for compression offloads the server CPU to achieve higher user density. Modern GPUs such as the NVIDIA Quadro and new VGX series offer serious processing power for real-time video stream encoding.

Using a Windows device to access your Windows virtual desktop continues to offer some special benefits. With Windows 8 and Windows Server 2012, desktop composition is performed by the Desktop Window Manager, a DirectX-based application previously best known for delivering the Aero theme in Windows 7. With Excalibur, we’ve taken the Aero Redirection feature of XenDesktop 5.5 and expanded it into Desktop Composition Redirection. All you need is a DirectX 9 or better graphics processor on the user’s Windows device. HDX queries the user’s Windows device to check that it has the required GPU capabilities and will automatically revert to server-side desktop composition if it does not. We can redirect Desktop Composition to capable client devices regardless of whether the Aero translucency effect is on (Win7) or off (Win8/Win7), sending the DirectX graphics commands to the user device for local rendering. Coupled with the improvements to bandwidth efficiency that we’ve made in Excalibur, the result of this unique HDX technology is such a high level of responsiveness and interactivity that you would never think your Windows 8 desktop was running in the cloud. HDX makes it feel just like local.

Derek Thorslund
Director of Product Management, HDX