On the day that Citrix released XenDesktop/XenApp 7.6 FP3, I was lucky enough to be at the UK Citrix User Group meeting in London, UK, where I was demonstrating some of the new graphics innovations in the release. One of the major features of this release is Thinwire Compatibility Mode.

What was brilliant so soon after the release was to see the response from users on twitter including some of those who had been at the demo and tried it out (including Neil Spellings CTP):

It was great to speak to a customer with real challenges with multiple factory sites on low-bandwidth who felt this could be the magic bullet. The technology has already been rolled out privately into production to several 10,000+ XenApp 2012 R2 where it’s solving bandwidth and legacy hardware constraints. However nothing beats seeing customers excited in person.

During its development and various private and public tech previews this feature has been known as Project Snowball/Thinwire Plus/Thinwire+/Enhanced Compatibility mode but in the documentation it is now “Thinwire Compatibility Mode”.

Make a humble engineer happy!

As the lead developer of this new mode, it was brilliant to meet real customers and see their delight and to hear their feedback. I’d love more people to try this out and let me know what they think, so I’ve added some details below on how to turn on and try out this mode and I’d really appreciate hearing your thoughts via the comments on this blog, below.

Key Features

You can read more details of this new graphics mode in the documentation, where it describes how Thinwire Compatibility Mode has been designed to take advantage of the architecture and technologies of how modern operating systems like Win2012 R2 and Windows 8.x up, construct the graphics of desktops. Specifically:

Intelligent bitmap matching for a bitmap-only provider. As much as possible, previously sent bitmaps are reused resulting in lower bandwidth.
• Bitmap translation analysis resulting in efficient window movement and scrolling.
• Higher default quality settings for lossy bitmap when compared to Legacy mode
• Emulated 16-bit mode, further reducing bandwidth for typical workloads.
• Improved transient detection for server rendered video content.
• Multi-transient handling for better multimedia experience e.g. when watching multiple videos
• Ultra-low server CPU usage, improving scalability.
• Fully backwards compatible, no need for client upgrades or hardware acceleration.
• Optimised for Cloudbridge acceleration
• Designed for port to Linux (already used by the Citrix Linux VDA)
• Adaptive display, tunable through the policy system
• ALL VDAs and Window OSs now supported (including new Windows 10 VDA) – (tech preview featured just Server 2012 R2 RDS)
• Completely new “Build to Lossless” mode for 3D Pro, faster responsiveness, better interactivity.
• Interruptible sharpening – allowing improved user experience on low bandwidth

By default HDX will still use H.264 based technologies if the hardware and Citrix receiver in your deployment can support them – so this new mode may need to be turned on, although it is now the default for end-points that can’t do H.264 so if you have a mixture of Receiver versions or end-client hardware levels, some users will get this mode automatically.

So how do I turn it on?

You can turn the new “Thinwire Compatibility Mode” on by explicitly turning H.264 off. This is done by setting the “Use video codec for compression” policy to “Do not use” will force session to use Thinwire Compatibility Mode by default.


With XD/XA 7.6 FP3, you don’t have to disable DCR as it is now disabled by default.

Because the FP3 release is a VDA-only update, to be able to use the new policies with FP3 you will also need to apply a small update your DDC. If you have stand-alone installations of Citrix Studio on other systems, those should also have the update applied in order to be able to see the new policies.

The file to install on your DDC is “CitrixGroupPolicyManagement_x64.msi”

After installing the update, your “Citrix Group Policy Management” version will appear in Control Panel, Add Remove Programs. Note that on Vanilla 7.6 DDC installations, this is a hidden component and will not be visible in “Add Remove Programs” before installing the Policy update.

How can I check what graphics mode I am using?

My colleague Amit has written a useful tool that allows you to survey all the receivers and sessions and check what graphics mode they are using, you can get it here. You can also follow the advice in this blog on how to check which graphics mode you are using. (If you are ever submitting an HDX bug – use the xml export feature of HDX monitor or the output of the wmic commands to provide information on the graphics mode).

When you are using “Thinwire Compatibility” mode you will see the encoder used to be the CompatibilityEncoder. This is a bit confusing, as earlier versions have a compatibility mode, which is completely different code and performance footprint (we generally don’t recommend the old one for general use as usually better performance available via other modes).

When we developed this new mode as “Project Snowball” we realised it out-performed the old compatibility encoder in every use case so we decided to completely remove it and replace it, rather than adding yet another encoder we kept the existing name. Personally I’m not sure this is the right decision still as there is a lot of existing advice advising people when not to use the old encoder and it has a completely different behaviour.