Multi-Stream Transport (MST) allows a single USB-C, USB4, or Thunderbolt port to drive multiple independent external monitors. This technology is driverless and can be used to seamlessly set up hotdesking or work-from-home environments. While MST is a standard feature on Windows and ChromeOS, hardware limits still apply. Even if a dock has four ports, your laptop’s internal graphics card (GPU) may only be able to drive two or three displays total.
1. Compatibility
Mac Users: To extend displays on Apple Silicon, use a DisplayLink dock or a Thunderbolt dock (for Pro/Max/M4/M5 chips).
2. Check Your Hardware’s "Display Limit."
Before buying an MST hub or dock for 2, 3 or 4 monitors, you must verify how many displays your laptop's GPU can handle. Note: The laptop’s built-in screen usually counts as one display.
- Intel Iris Xe / Core Ultra: Generally supports up to 4 displays total (e.g., the laptop screen + 3 external monitors).
- Entry-level AMD/Intel (Celeron/Athlon): May be limited to only 2 displays total (laptop screen + 1 external).
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Snapdragon X Elite: Generally supports up to 4 displays total (e.g., the laptop screen + 3 external monitors).
- ARM Compatibility varies by the specific chip.
- Some SoCs, such as the Texas Instruments DRA829J, do support MST, while others, such as the MediaTek MT8127, do not. Always check your SoC's technical datasheet for "DisplayPort MST" support.
Tip: If you want to use 3 external monitors and your laptop is limited to 3 total displays, you may need to close the laptop lid to "disable" the internal screen and free up a display slot for the third external monitor.
3. Plugable MST & Hybrid Product Guide
Important Note on the UD-3900C4: This is a "Hybrid" dock. HDMI ports 1 and 2 use DisplayLink (drivers required) and do not count toward your GPU's MST limit. HDMI ports 3 and 4 do use MST and require your laptop's hardware support.
4. Bandwidth: The "Pipe" Problem
Think of your USB-C port as a water pipe. MST splits that pipe. If you try to push three 4K signals through a small pipe (older DP 1.2), the screens can flicker, disconnect or drop to low resolution. It is essential to use certified, high-quality cables to ensure stable and full-bandwidth video transmission.
Maximum Performance Matrix
5. Troubleshooting and FAQ
- "Only one or two of the connected monitors are functioning.": Try closing your laptop lid. If the second or third monitor powers on, you have reached your GPU's maximum display count.
- "The 4th monitor on my UD-3900C4 is mirroring.": This means your laptop likely does not support MST, or you are on an Apple system.
- "I have a Mac, and it's mirroring.": This is the expected behaviour, as Apple does not support Multi-Stream Transport (MST).
- For base Apple Silicon models, you must use DisplayLink technology to overcome limitations of external displays. However, if you have an M4, M5, or a Pro/Max version of Apple silicon, a Thunderbolt docking station can also be used to extend your displays.
5.1 Connection Issues: USB-C & Video Cables
The cables you use are just as important as the dock itself. High-resolution multi-monitor setups require high bandwidth.
- Always use the USB-C cable that was provided with your Plugable dock. This cable is specifically rated to support DisplayPort Alt Mode and the dock's power delivery requirements.
- For best results, use cables that support DP 1.4+ with a maximum bandwidth of 32.4 Gbps. This provides enough room for two 4K UHD streams at 60Hz.
- Use the cables included with your monitors. If you experience flickering or lower-than-expected resolution, try swapping the cables to rule out a faulty or low-bandwidth cable.
5.2 Driver & OS Maintenance
To ensure a stable connection, your software must be up to date with your hardware.
- Ensure Windows or ChromeOS is fully up to date.
- Outdated Intel, NVIDIA, or AMD drivers are a common cause of MST failure. Visit your laptop manufacturer’s website to download the latest graphics drivers.
- If a monitor isn't detected, try a "Power Cycle": Unplug the dock from the laptop, power it off, wait 30 seconds, then reconnect.
Still Unsure?
Email support@plugable.com with your laptop's model number and the monitors you plan to use and we will do our best to determine if an MST solution is right for you.
