The external display dilemma for MacBook users
As a MacBook Air M1 user, I was initially drawn to Apple's sleek design, impressive efficiency, and fluid ecosystem. However, as my workload became more complex, the need for more screen space became undeniable. I wanted to connect three external displays and expected a straightforward setup—only to encounter a snag.
Connecting a second monitor didn't expand my workspace; instead, I got a mirrored image or, even worse, no screen recognition at all. Thorough research in online forums confirmed my frustration: Due to hardware limitations, M1 and M2 MacBooks do not natively support multiple external displays.. Even with multiple Thunderbolt 3 or 4 ports, these devices do not natively support Multi-Stream Transport (MST) – a feature widely used on Windows PCs to drive multiple monitors over a single connection.
For reference, the following MacBooks with Apple Silicon only support one external display:
- M1 MacBook Pro 13"
- M2 MacBook Pro 13"
- M1 MacBook Air
- M2 MacBook Air
- M3 MacBook Air (with the lid open)
- M3 MacBook Pro 14" (with the lid open)
Are Mac users therefore limited to a single external monitor? Fortunately not. The solution lies in... DisplayLink technology, a widely used method to enable multiple external displays on Apple Silicon Macs.
How DisplayLink works
DisplayLink technology works via two core components:
- A Virtual Graphics Card (VGC) driver, which is installed on the Mac and functions as an additional GPU.
- A hardware rendering engine (HRE), which is embedded in the DisplayLink adapter or in the docking station.
The DisplayLink driver (VGC) captures the GPU output, compresses the virtual screen data using an adaptive encoding algorithm, and transmits the compressed video stream via USB. The DisplayLink device then decompresses the data via the HRE and converts it into a standard DisplayPort or HDMI signal, allowing multiple external monitors to work seamlessly.
A major advantage of DisplayLink is the USB 3.0 compatibility, This means that neither Thunderbolt 3 nor 4 is required. Whether you use USB-C, USB-A, or a Thunderbolt docking station, DisplayLink is highly adaptable to various Mac setups.
TL;DR: The solution for multi-display Mac users
If you are a M1/M2 MacBook Pro or MacBook Air own and two or more 4K displays If you want to connect, your best choice is a DisplayLink docking station or a KVM switch. While DisplayLink introduces low latency, it remains within acceptable limits for regular productivity tasks. as long as the USB bandwidth is not heavily used.
Currently, most DisplayLink docking stations on the market only support dual-display setups. If you need triple-display support, I recommend the TESmart KVM switch.Furthermore, if, like me, you need a device that can connect and display two computers simultaneously and allows easy switching, the TESmart KVM switch is the ideal solution.
Practical performance test
Since I frequently switch between my MacBook Air and a desktop workstation When I switched, I chose the TESmart HDC203-PM24 KVM switch decided, who the DL-6950 chipset used and 4K60 Multi-Display Setups supports.
After connecting the KVM switch to the MacBook, you can see information from three displays in the system report. All three screens are running at a resolution of 4K at 60Hz. (HiDPI was disabled here.)
Because DisplayLink uses software to compress video signals, it places a heavy load on the system's CPU. With rapidly changing video content, the CPU requirement increases compared to static displays. Now let's take a look at real-world performance and test DisplayLink's latency in various scenarios, such as mirrored and extended displays, different content types, and system loads.
Test setup:
- Three monitors connected simultaneously
- Custom script to display timestamps
- Local video playback via QuickTime Player
- Online video streaming via Safari: https://www.youtube.com/watch?v=linlz7-Pnvw
- Browser performance test: https://browserbench.org/Speedometer2.0/
- Gaming video: https://www.youtube.com/watch?v=MguHX7p4jA4
- iPhone 15 Pro used for recording
Test with DisplayLink in mirror mode
To compare the performance of DisplayLink displays in terms of latency and frame rate, we first set the DisplayLink display to mirror the MacBook screen.
- Left: MacBook screen
- Right: DisplayLink display connected via TESmart KVM switch
Latency test at idle
At idle, the latency between the DisplayLink display and the built-in display is almost negligible.
Latency test during local 4K60Hz video playback
The latency reaches 25ms during local 4K60Hz video playback.
Latency test during online 4K60Hz video playback
Interestingly, there's no noticeable latency here. Why? Let's look at the CPU usage:
