Run 4 monitors from a laptop?

[tl;dr: Yes you can drive 4 monitors each with different content from most PC laptops. But there are some gotchas. For best results, start with a regular dock station NOT powered by DisplayLink technology for the first two monitors, then add a DisplayLink-based video extender device to that.]

Introduction

Many laptop users only view the built-in laptop screen but some need more real-estate. Almost all laptops can drive a single external monitor by plugging the monitor directly into the laptop with a cable. Two monitors can be plugged into most laptop docking stations with distinct content on each. There are many docking station styles which use one of the following connection schemes:

1. Proprietary connector (MS Surface, old HP workstations, etc.)
2. USB-C connector with DisplayPort alternate mode (check the laptop and dock manufacturer’s website for compatibility)
3. Thunderbolt 3 (same physical connector as USB-C but with different software protocol)
4. USB A or USB-C with DisplayLink technology (not recommended for connecting the first two monitors of a three or four monitor array)

Options 1-3 are great for moderate rigs with two monitors, but what if you need more?

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Brief history lesson

Back in the Windows Vista timeframe, there were vendors offering VGA-over-USB-2.0 solutions where you plugged a little dongle into a standard USB A port to get an extra VGA or DVI monitor output. Performance on these early USB-video dongles was poor with significant lag/latency and frequent glitches. This was due to a reliance on software which essentially hacked into the Intel, AMD, or NVIDIA GPU device drivers with a method that was not well-vetted by Microsoft or the GPU vendors. When windows update service packs were applied, the method would break leaving the screen blank and you’d have to wait weeks or months for fixes.

With Windows 10, Microsoft introduced an indirect display model which prescribes reliable and reasonably performant methods to attach displays to USB without a direct GPU connection. Monitors attached this way with the latest chipsets still do not perform as well as monitors connected directly to a GPU. They usually have an added lag/latency of 3-6 frames at 60Hz refresh (50-100ms) which makes gaming awful – but most office applications work OK. Below, a handful of devices using these newer software interfaces and chipsets are listed. These devices can be used to add 1-2 additional monitors at 4K resolution to your laptop, existing docking-station, or desktop beyond the 3-screen limitation of most GPUs.

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Note: Because of the latency issues with USB extenders and Docks designed around DisplayLink technology, it is best to start with a regular docking station first. For example, on a Microsoft Surface, get the Surface Dock station for the first 2 monitors, then add a third and fourth with a video extender. Or on a Lenovo, start with a USB-C or Thunderbolt 3 dock which takes advantage of DisplayPort alternate mode and add a third and fourth monitor with a video extender.

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USB-C/USB 3.x Video extenders supporting 4K

DevicePC portMonitor #1 portMonitor #2 portMax resolution/ refreshOther portsChipset Technology VendorApproximate Price ($USD)Plugable USB-C-6950-DPUSB-CDisplayPortDisplayPort4K60EthernetDisplayLink/ Synaptics~$85-100Plugable USBC-6950-HDMIUSB-CHDMIHDMI4K60EthernetDisplayLink/ Synaptics~$85-100StarTech USBA2DPGBUSB ADisplayPortDisplayPort4K60EthernetDisplayLink/ Synaptics~$80-100Plugable USB3-6950-HDMIUSB AHDMIHDMI4K60EthernetDisplayLink/ Synaptics~$85-100Plugable UGA-4KDPUSB ADisplayPortN/A4K60N/ADisplayLink/ Synaptics~$60-75StarTech USB32DP4KUSB ADisplayPortN/A4K60N/ADisplayLink/ Synaptics~$60-75Plugable UGA-4KHDMIUSB AHDMIN/A4K60N/ADisplayLink/ Synaptics~$60-75StarTech USB32HD4KUSB AHDMIN/A4K30 or 1080p60N/ADisplayLink/ Synaptics~$50-60StarTech USB32HD2USB AHDMIHDMI4K30 or 1080p60N/AMCT~$50-75StarTech USB32DPES2USB ADisplayPortN/A4K30 or 1080p60N/AMCT~$50-60

Less expensive USB video extenders exist from a variety of manufacturers in the $20-$75 price range with varying capabilities, performance, and vendor support. I’ve had the best luck with Plugable and StarTech devices based on the latest DisplayLink/Synaptics chipset technology and only use these brands on customer builds.

USB-C DisplayPort Alternate mode and MST hubs

Many modern laptops include built-in USB-C, Thunderbolt 3, or DisplayPort receptacles. When monitors are connected to these ports, they use the laptop’s GPU directly so there is no added lag/latency. But not all USB-C ports support this direct connection to the GPU. In order to support it, the USB-C port must enable “DisplayPort Alternate mode”. Unless your laptop manufacturer indicates monitor connectivity offered by the USB-C port, it may only be suitable for data and/or charging. Also, the specific monitor capabilities such as resolution and refresh rate offered by the port can differ between laptop models. For example, here is an article describing the differing monitor support for Microsoft Surface device USB-C ports.

Even if your laptop only has 1 monitor output port via USB-C or DisplayPort, you may still be able to connect multiple monitors directly to the GPU with MST technology. MST stands for “multi-stream-transport” and is a method to split a DisplayPort signal into multiple monitors by sharing the bandwidth between them. This technology is specific to DisplayPort (and USB-C with DisplayPort alt mode) and can either be implemented via a discrete MST hub, a docking station with a built-in MST chipset, or a daisy-chain output port built into a monitor. Windows and Linux support MST well, but MacOS does not. Most laptops limit the number of distinct screen outputs to 3 (including the built-in laptop screen if it is switched on). So if you try to connect additional monitors beyond this limit, they will go blank or display the same content as one of the other screens. (DisplayLink and similar video extender technologies have no such 3-screen limitation.) Many OEM docking stations have a built-in MST hub to provide two monitor outputs. Using an additional MST hub in tandem with these docking stations to gain a third output is not recommended. The following table compares MST hubs vs USB video extender technology:

Performance characteristicMST HubUSB Video extender adapter/dongleAdded Latencynegligible50-100msMaximum # of screens 37 (up to 15 is technically possible but impractical)Maximum screen resolution1080p – 8K30 depending on PC4K60 (5K60 in when combining two outputs/cables to a single compatible monitor)Maximum refresh rate60Hz – 240Hz depending on PC (60Hz is typical)60HzRequires external powersomeno (Docking-station-class devices with multiple USB ports do require external power)OK for office apps?yesyesOK for intensive video and 3D graphics apps?yesmostOK for casual games?yesmostOK for intense 3D games?yesnoUses CPU cycles?noyes (negligible CPU load for most applications on modern PCs)Has additional USB, audio, or Ethernet ports?no (additional ports available on docking-station class devices)additional ports available on some modelsUses which port on the laptop?DisplayPort, miniDP, or USB-C depending on modelUSB-C or USB A depending on modelCascade multiple hubs Not recommended (Connecting an MST hub to a device that already has an MST chipset such as many OEM docking stations often won’t work and one screen will be blank.)Not recommended (Downstream USB ports on Docking-station class devices can be used for connecting an additional Video extender, but may yield poor performance)Monitor Daisy-chain supportSome – Daisy chaining compatible monitors from a single port may work on some modelsnoCost ($USD)~$50-130 for name brand devices~$50-100 for name brand devices

A variety of MST hub styles are available:

More info

Chipset technology vendors for USB-based video extenders

Note: products based on different technology vendors conflict with each other and cannot be used together on the the same system. You must completely uninstall any software from one vendor in order to switch to a product from another vendor. For example, DisplayLink provides explicit instructions on removing other vendor’s software.

MacOS support

These devices are not well-supported on the latest versions of MacOS. Check with the underlying technology vendor.

DisplayLink vs DisplayPort

DisplayLink is the name of a company while DisplayPort is the name of an open video electronics standard for monitor connectivity that describes a physical port and signaling standard and makes recommendations on software/hardware implementations for that port.

The company name DisplayLink was chosen during the time period when DisplayPort was already in development but not yet widespread and has caused confusion among consumers and IT professionals. Remember that when connecting a monitor to any computer – DisplayPort directly connected to a GPU is always better than via DisplayLink. DisplayLink inserts an additional layer of software and hardware in between the GPU and the monitor which *always* compromises performance to some degree. DisplayLink and similar technologies should only be used when all direct connections to the GPU have been exhausted or when those connections offer limited resolution/refresh rate capabilities that is unsuitable for the intended monitors.

Alternatives to multiple monitors

Instead of getting multiple small monitors, consider getting a single 43″-class 4K Home Theatre screen with HDMI 2.0. These screens are compatible with PCs and for their size are considerably less expensive than the combined cost of multiple PC monitors. For multi-tasking, there are a multitude of 3rd-party apps to make it simple to arrange your applications such as Microsoft Powertoys. Below, the benefits and drawbacks of PC vs Home Theatre screens for Desktop computing are compared

Performance characteristicTriple 1080p or 1440p PC monitors4K 43″ class Home Theatre monitorAdded Latency/ Response timenone, except when adding a 4th screensome on cheaper modelsConnector stylesDisplayPort, HDMI, DVI, and/or USB-C depending on modelHDMI onlyRefresh rates60Hz – 360Hz depending on resolution; free-sync/G-sync available for gaming60Hz (240Hz with interpolation which is not useful for gaming)Aspect ratios available16:9, 16:10, 21:9, 32:9, etc.16:9VESA arm mountableMost with 100x100mmMost with 200x200mm or 100x200mmBezelsThin bezels available; bezels between screens can help some users arrange apps but can otherwise be disruptive Thin bezels available; 3rd-party software tools can help arrange appsDEsigned Viewing distance2-3 feet (50-100cm)6-10 feet (2-3m)Pixel density~82-144 ppi depending on resolution & size~100 ppi (lower for larger screens)Color reproductionVarious modes available for print, photo, film, video, gaming, etc.Optimized for movies, TV, and console gamingHigh Dynamic RangeAvailable, but not commonAvailableBrightness300+ nits600+ nitsOTA HDTV tuner built-innoyesCost ($USD)$300+$250+

• 4K 43″ class Home Theatre monitors with HDMI 2.0