What is Mux Switch? – Explained

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The Beggining

Mux switch is actually fairly simple. Laptop manufacturers incorporate a small device on the motherboard paired with programming logic. This assists in switching between the iGPU and dGPU. Think of it as there’s a direct line between the display and the mux switch. Which then is used to determine what GPU should be used for certain scenarios.

Prior to mux switches being more mainstream software handled the “switch/activation” between GPU’s. And, the iGPU was/is mirrored to the dGPU. Which created a high level of latency causing the iGPU to become a bottleneck. Without a mux switch, you won’t see the maximum performance of the dGPU whatsoever due to that bottleneck.

Asus Zephyrus Duo 15se is one of the laptops that I was very excited about testing out for a long time. Well, that excitement did not last very long after receiving the unit though. I was facing serious stuttering and lagging issues that I could not seem to resolve.

What is Mux Switch? – in detail

Mux switch is hardware installed on your laptop by the laptop manufacturer. It basically is a multiplexer that allows you to directly connect the display to the dedicated graphics card instead of the internal GPU.

All laptops have a default graphics processor, they are called internal GPU (iGPU), and any other graphics card installed in addition to that is called a dedicated or external graphics card (dGPU).

By default, the internal laptop display is directly connected to the iGPU as it improves the battery performance and the majority of the tasks can be handled well by the laptop’s iGPU. Any processing done by the external display card is also passed through and processed by the iGPU. You can already see that this creates a bottleneck problem if the dedicated graphics card is processing and transferring a lot of data to the iGPU to process and transmit to the internal display or the display by itself.

Setup With A MUX Switch And Direct Output Displays

Now, let’s see what happens if there is a MUX switch present in a laptop and after that, I’ll discuss a little about Nvidia advanced Optimus and a workaround if you don’t have a MUX switch. This image might look very confusing at the beginning, but let me explain what is the use and advantages of having a mux switch. If you look carefully in the image, the mux switch is directly connected to the internal display and the external display output port.

When the switch is enabled, the graphics card directly sends output to the monitors instead of going through the internal display card which was creating a bottleneck. I’ve explained this in laymen’s terms and I am pretty sure there is more to it than just that, but that’s the no.1 reason why having a mux switch is so important to make sure you get the best out of it in your graphics card and your high-end laptop.

Lagging And Stuttering Issues

The problem with the Zephyrus DUO 15 SE was that it has two high-quality displays itself. So basically they are using so much of the iGPU processing the content. And the latest AMD R9-5900HX looks like was throttling the CPU on top of that. I have seen reports of R9-5900HX throttling the CPU right. When it needed to actually boost the performance even in normal process temperature without the CPU getting too hot.

The Zephyrus DUP’s HDMI output is connected to the internal display and not the dedicated RTX 3080X that I had. If you see carefully in the image above. The red arrow shows the connection between the graphics card and the output port. So if you connect a monitor to that external port. It will skip the iGPU processing and makes full use of the graphics card. For you to skip iGPU processing and fix this lagging and stuttering issue on the Zephyrus DUO. Try connecting it to the USB-C port at the back, that is connected to the graphics card directly.

Check Where Your Display Output Port Is Connected To

If you have an Nvidia graphics card you can easily check what kind of setup does your laptop has. Open the Nvidia Control panel. You can open the start menu or just search for “Nvidia Control Panel” in the bottom left corner search bar. If you look in the screenshot below, all the output display ports are connected to the Nvidia graphics card. I had a similar setup in my 2015 Acer Nitro that I had for more than 5 years now.

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