Can a Motherboard Bottleneck a GPU?

Succinctly, yes, your motherboard can bottleneck your GPU if it isn’t fully compatible with the motherboard you’ve installed.

There are two ways your motherboard may begin to bottleneck your GPU, but it’s worth exploring the concept of bottlenecking to begin with. After all, we can tell you that your motherboard is bottlenecking your GPU, but that doesn’t mean anything if you don’t know what bottlenecking is.

Let’s take a deep dive into bottlenecking and see how we can prevent this issue within our PC builds.

What Is Bottlenecking?

You know how when you pour the liquid out of a bottle it takes extra time because the opening of the bottle is smaller than the container? This is what a bottlenecked GPU does with the data its processing.

When a processing component in your computer is bottlenecked, the processor will process data faster than the computer can display and use it. This is usually caused by outdated or incompatible chipsets that cause the component to run in a compatibility mode where the power is actively reduced to match an older chipset that had fewer capabilities than the modern chipsets.

Bottlenecking tends to be pretty marginal and is generally only seen from high-end graphics cards which have higher throughput thresholds than some older (and some modern) motherboards can withstand. In these cases, the bottleneck may not even be noticeable when playing games or doing other computing tasks. Low-to-mid range GPUs rarely, if ever, get bottlenecked because of their lower processing thresholds.

How Can a Motherboard Bottleneck a GPU?

People often assume that all graphics cards are compatible with their motherboard, but this simply isn’t true. While the PCI and PCIe slots that your GPU will be seated in may be standardized, thus all graphics cards will be able to fit into the board, this doesn’t mean the graphics card is completely compatible with the board. It just means the graphics card can be seated on any board.

As we’ve mentioned, incompatible graphics cards may result in a bottlenecked experience and graphical interruptions when doing intensive tasks like digital art, video production, or while gaming you may notice graphical slowdown from bottlenecking.

The first way is if your motherboard’s PCIe slot is an older generation than the graphics card. While newer graphics cards tend to be backward compatible, they can’t brute-force through the limitations of the technology’s generation.

Additionally, if your PCIe slot does not have the correct number of lanes to run your graphics card at its highest speeds, your motherboard will naturally bottleneck your GPU to bring the speed in line with what’s possible with the slots and lanes you have available,

PCI/PCIe Interface: the Basics

The PCIe interface is the connection that your computer’s motherboard makes with PCIe devices. Particularly old PCs may use an older generation of the interface known as simply “PCI” interfaces. Most PCIe cards are backward compatible with PCI slots but will experience an even greater bottleneck than cards that are using earlier generations of PCIe slots.

Graphics cards are PCIe devices, but they aren’t the only PCIe device you can install into your computer. PCIe slots can be used for things like graphics cards, audio cards, Wi-Fi connectors, Bluetooth connectors, or SATA controllers.

PCIe slots come in various sizes ranging from x1 to x16, the number after the x refers to the number of PCIe lanes the slot offers for devices using it. It can be confusing to determine what kind of PCIe slot your motherboard comes equipped with because a x4, x8, and x16 slot can all be the same physical size. The only way to know how many lanes each slot comes equipped with is to read the spec sheet for your motherboard.

Differences Between the Generations of PCIe Interfaces

With each new generation of PCIe Interfaces, the individual lane speed is generally doubled from the previous generation; an x1 PCIe 3.0 slot can support speeds up to 0.985GB per second while an x1 PCIe 4.0 slot can support speeds up to 1.969 GB per second. This influences how fast the slot is able to process the data from the device installed in it.

Newer PCIe slots can support more demanding and intensive devices like high-end graphics cards, while older slots will not be able to support these devices running at their full speeds. Here are the top speeds for each generation of PCIe slots.

1.00.250 GB/s0.500 GB/s1.0 GB/s2.000 GB/s4.000 GB/s
2.00.500 GB/s1.000 GB/s2.0 GB/s4.000 GB/s8.000 GB/s
3.00.985 GB/s1.969 GB/s3.938 GB/s7.877 GB/s15.754 GB/s
4.01.969 GB/s3.938 GB/s7.877 GB/s15.754 GB/s31.508 GB/s
5.03.938 GB/s7.877 GB/s15.754 GB/s31.508 GB/s63.015 GB/s
6.07.877 GB/s15.754 GB/s31.508 GB/s63.015 GB/s126.031 GB/s

While we have the numbers that will eventually be introduced with PCIe 5.0 and 6.0 interfaces, those interfaces have not yet been produced for the public. PCIe 4.0 is the latest commercially available PCIe interface as of the writing of this article.

Since graphics cards—especially high-end ones—require high data transfer speeds to run at their optimal speeds, you’ll want to slot your graphics card into an x16 slot if you have one. This will ensure that your graphics card is able to run at the highest speeds it can withstand and improve your graphical performance.

As a rule of thumb, you can expect the first PCIe slot on your motherboard (from the top) to provide you with the full 16 lanes that you need to run your GPU at its maximum speeds. The second and third slots will generally provide fewer lanes, most will be x8 or x4, but you may see some cheaper motherboards with x1 and x2 lanes as well.

Issues When Installing a GPU into x8 Slots Compared to x16 Slots

In general, you want to install your graphics card into the x16 slot on your motherboard, as the Pudget Systems Performance Report did show noticeable bottlenecking when they tested an NVIDIA Titan X PCIe 3.0 card in both an x8 and an x16 slot.

Pudget Systems tested the NVIDIA Titan X in both slots while running various software and games and found that high-end GPUs like the Titan X will suffer from significant bottlenecking when used in x8 slots.

Issues When Installing PCIe 4.0 Cards into PCIe 3.0 Slots

Pudget Systems also tested PCIe 4.0 cards by installing them into PCIe 3.0 slots to see if there were noticeable degradations of quality when performing graphically intensive tasks like gaming and digital design.

As expected, the card’s scores degraded significantly when the card was installed into a lower generation slot. When conforming to the older data transfer speeds of the PCIe 3.0 slot, the bottlenecking is significant enough to cause the GPU to run at slower speeds to keep it from overloading the slot.

Futureproofing: Can You Do It?

It’s hard to future-proof a build in totality. However, it’s possible to give some extra thought to the pieces that you choose. This article and others like it are a good place to start since they allow you to learn more about the current technology.

If you’re trying to make the best purchases for the future, it’s also worth doing some extra research about up-and-coming technology. If you see that a new technology is becoming more readily available, see if it’s something that will imminently be available to the public; you may want to wait for the release of new technology if there’s some on the horizon. Otherwise, your current technology might become obsolete faster than you’d like.

Final Thoughts

Bottlenecking may not be a huge problem for people who don’t do graphically intensive tasks but knowing what it is and how to avoid it is a critically important skill for those who are building their own computers. After all, you want to get the most out of every component that you purchase!