Citrix Virtual Apps and Desktops 7 (f.k.a. XenApp and XenDesktop) supports a variety of display configurations across different endpoint devices. The purpose of this knowledge base article is to review product capabilities and support requirements with regards to display resolutions, multi-monitors, and DPI scaling configurations for the client endpoint. Deployment considerations related to performance and scalability are also included.
Display resolution standards
As of this writing the most common resolution for a desktop monitor is 1920×1080, also referred to as 1080p. The term “4K” is used to refer to a monitor that has a resolution in the order of 4000 pixels in one dimension, see 4K Resolution-Wikipedia. It is important to establish the resolution of a particular 4K monitor. In the context of this article we refer to 4K resolution as 3840 x 2160 (or 2160p) which is the most common standard based on the aspect ratio of 16:9. These ultra-high-resolution monitors are becoming more prevalent in the Enterprise with the arrival of new mobile devices (laptops and tablets) and as the traditional 1080p monitors get replaced during hardware refresh cycles.
Display resolution and multi-monitor support in the Citrix session
The maximum resolution and number of monitors that can be used in a Citrix session is determined based on the display adapter in use. A Citrix session may use different display adapters, each with its own set of capabilities depending on the virtual desktop agent (VDA) type and the operating system (OS). There are other factors to consider as well such as the presence of a graphics processing unit (GPU) and the HDX graphics mode in use. Supported configurations and deployment considerations are listed below:
- Server OS VDAs (Virtual Apps / XenApp) – Supports up to 8 monitors. Display resolution is only limited by the Windows OS capabilities or the available video memory for the machine. The amount of video memory that a Citrix session can consume can be configured via Citrix policy. The default value for the Display memory Limit policy is 65536KB and this is sufficient for up to 2x4K monitors (2x32400KB).
- Desktop OS VDAs (Virtual Desktops / XenDesktop)
- Windows 7 – Supports up to 8 monitors. Display resolution is limited to 4094 pixels in any dimension. The VDA must have sufficient memory allocated to support the desired configuration. Refer to CTX200257 – Screen Issues Connecting to 4K Resolution Monitors for additional information.
- Windows 10 – Supports up to 8 monitors. Display resolution is limited to 4094 pixels in any dimension on 7.15 LTSR VDAs. On 7.16 and greater VDAs, display resolution is only limited by the Windows OS capabilities or the available video memory for the machine. The amount of video memory that a Citrix session can consume can be configured via Citrix policy. The default value for the Display memory Limit policy is 65536KB and this is sufficient for up to 2x4K monitors (2x32400KB).
- GPU-enabled Desktop OS VDAs (HDX 3D Pro) – Maximum resolution and number of monitors is strictly dependent on the GPU capabilities. For example, supported NVIDIA GPUs may support display resolutions up to 4096×2160 and up to 4 monitors depending on type or vGPU profile and license in use. Refer to CTX131385 – HDX 3D Pro GPU Support and Deployment Considerations for more information.
- Linux VDAs – Standard VDAs support up to nine monitors, and HDX 3D Pro VDAs support up to four monitors. The Linux VDA provides the out-of-the-box multi-monitor support with a default resolution of 2560×1600 per monitor. Refer to CTX220128 – How to Configure Multi-Monitor Support on the Linux VDA for more information.
Note: While there are no controls in place to limit resolutions above 4K in Windows 10 VDAs, Citrix development testing is limited to 4K monitors currently.
High-DPI (dots per inch)
Current support for High DPI endpoints is based entirely on the Citrix Receiver or Workspace App capabilities for a given platform. Citrix Receiver for Windows 4.10 (or greater) and Citrix Workspace App for Windows are the only DPI aware clients available currently. These clients can be configured to either scale the session or ignore DPI settings and set the native resolution on the VDA. Refer to CTX230017 – Display DPI scaling configuration with Receiver for Windows for additional information.
Clients that are not DPI aware rely entirely on the OS to scale the application as appropriate to the endpoint DPI settings. This means that the Receiver or Workspace App can behave differently depending on the OS. Multi-monitors with different DPI scales are not supported with clients that are not DPI aware.
Performance and scalability considerations
In the context of display remoting the size of a user session can vary significantly based on display resolution and the number of monitors alone. As the session grows in size more server and client resources are required, for rendering and encoding/decoding of the graphics, and more data needs to be sent from the server to the client via the network. This has a direct impact to session performance and server scalability. Citrix highly recommends taking user requirements with respect to display configuration into account as it relates to server hardware, network links, and endpoint devices. Some deployment considerations are listed below:
- Both display resolution and the number of monitors increase the session size. A user connecting from and endpoint with a single 4K monitor would result in the same session size as a user connecting with four 1080p monitors. Single server scalability can be reduced significantly by simply upgrading user endpoints with 4K monitors. If 4K monitor support is required additional server resources should be allocated accordingly to maintain desired user density levels.
- Bandwidth requirements will also increase with higher resolutions and the number of monitors in use. Bandwidth constraints could limit frame rates and reduce image quality affecting session interactivity and user experience as a result.
- The endpoint device must have adequate hardware resources available to support the desired display configuration. This could mean having enough CPU resources and in some cases a GPU that can handle the graphics workload. Performance limitations of Thin Clients may become apparent at high resolutions such as 4K, for example.