Using 3 Monitors with Carbon X1

[ADIST]

Can I use three external monitors by disabling the display on a Carbon-X1 laptop, Core I7-10510u CPU @ 1.8GHz 2.30GHz, and an Intel(R) UHD Driver on Windows 11? I am using a Thinkpad 40AH docking station using the two display ports to run two external monitors with the laptop display. I tried disabling the laptop display and wiring a third monitor using the USB c port on the docking station and the display input on the third monitor, but the monitor could not be detected. Any help would be appreciated.

[megan3000]

The CPU does support 3 displays, simple and easy...

However, what the laptop and the docking support (how many displays and what resolutions, etc) is another story, and only Lenovo can tell you that...

Quick question: Are you sure that the USB-C port on the docking has video output functionality? (Display Port mode)

Checking Lenovo's info, I'm seeing that the docking 40AH only supports 2 external displays, and only through the DisplayPort ports...

https://pcsupport.lenovo.com/us/en/solutions/pd029622

Also, the specs in this link ( https://support.lenovo.com/us/en/solutions/pd500174-thinkpad-pro-docking-station-overview-and-service-parts ) shows the USB-C port as a regular "data port" (with just a low data transfer rate of 5GBs)

(Another possibility is a bandwidth limitation due to the number of display and if using higher resolutions/refresh rates)

[n_scott_pearson]

Your 10th gen processor only supports DisplayPort 1.2. This means that all of the monitors you connect to that docking station are sharing the bandwidth of this one DisplayPort 1.2 channel. If you are using monitors with only 1080p resolution, then three monitors can be connected at up to 85Hz (combined bandwidth required is 13.77Gb/s and available is 17.28Gb/s). If the monitors are running at a higher resolution, then chances of success drop. For example, supporting three 1440p monitors at anything better than 30Hz is questionable (technically, the bandwidth requirement for 60Hz is 16.89Gb/s and still below the maximum, but I haven't seen anyone claim they made it work).

In many - but not all - laptop designs, closing the lid disables the display and it doesn't count against the processor's 3-monitor support limit. In this case, however, it doesn't matter - you simply cannot connect a third monitor to the USB-C port on this dock. This port is a USB-only port; there is no support for DisplayPort Alt Mode. Once the DisplayPort signal encounters the MST Hub in the dock, that's the end of the line. Unless they have a different version of this dock with three display connectors, you are not going to connect three monitors via the dock.

The processor has three display channels. One is used for the Embedded DisplayPort (eDP) display. One is passed to the dock. That leaves one more. If there is another display connector - on the laptop itself, for example - you may be able to connect the third external monitor there.

Hope this helps,

...S

[ADIST · Accepted solution]

Thank you both for your feedback. I tried using an HDMI cable directly to the third monitor from the laptop port. Once I changed the settings for the Laptop lid to do nothing when it was closed...it worked. I now have three external monitors!