For reference, the UD-7400PD is a ‘hybrid’ docking station that uses two different technologies in order to drive the connected displays. The first technology is USB-C Alt Mode Video, and the second technology is DisplayLink.
The capabilities of each technology vary, and the total number of displays connected to the dock will also have an effect on their respective maximum resolutions and refresh rates.
For this example, we will separate them into two different groups:
- Alt Mode Video output capabilities
The UD-7400PD’s ‘HDMI 8K Alt Mode’ video output (labeled port #1) is driven by the USB-C Alt Mode video output of the host computer. The capabilities of this output will vary depending upon the specifications of the host computer’s USB-C port.
To expand further, the video output capability of a host computer’s USB-C port is determined by two different factors. The first is the amount of video bandwidth available, and the second is whether or not a form of video compression is available.
The amount of video bandwidth provided by a USB-C port is commonly referred to as ‘HBR2’ or ‘HBR3’. This stands for ‘High Bit Rate’ version 2 or 3. The higher the number, the more bandwidth is available. For example, HBR3 provides more bandwidth than HBR2.
For host systems that support HBR3, there is an optional feature known as ‘Display Stream Compression’ or DSC. DSC is a visually lossless compression mechanism that allows for more video information to be provided.
The table below lists the maximum resolution and refresh rates possible via the ‘HDMI 8K Alt Mode’ video output (labeled port #1) as determined by the specifications of the host computer’s USB-C port:
| Host USB-C port specification | Maximum Resolution of ‘HDMI 8K Alt Mode’ output |
| HBR3 with DSC | 7680 x 4320 @ 30Hz ** |
| HBR3 | 3840 x 2160 @ 60Hz |
| HBR2 | 3840 x 2160 @ 30Hz |
** Note, when used with a Mac host the maximum resolution supported will be 6016x3384 @ 60Hz. **
*** Note, if you are unsure of the specifications of your computer’s USB-C port please reach out to your computer manufacturer for additional information. ***
- DisplayLink video output capabilities
The UD-7400PD can drive up to four external displays via the DisplayLink DL-7400 chipset within the unit. One of the four video outputs of the DL-7400 chipset is routed to the ‘HDMI DisplayLink’ video output (labeled port #2).
Regardless of the capabilities of the host computer’s USB-C port, the maximum resolution and refresh rate of the ‘HDMI DisplayLink’ video output (labeled port #2) will always be 3840x2160 at 60Hz.
Three of the four video outputs of the DL-7400 chipset are routed to the three ‘USB 10Gbps + DisplayLink’ ports (labeled #3, #4, and #5).
The capabilities of these ports will vary depending upon the total number of connected displays connected to the dock, and the specifications of the host computer’s USB-C port. A table listing all of the possible resolutions as determined by the specifications of the host computer’s USB-C port and the number of displays connected to the dock is available here → LINK
