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Which PCIe Slot for GPU? – Learn Here

For many custom PC builders, the GPU is one of the most important peripherals that gets added to the computer, and for good reasons.

From simulation to gaming, graphics card is an essential component for most professional PC builds.

On top of that, with NVIDIA’s SLI technology and AMD’s Crossfire, you can use two or more compatible graphics cards together as one, letting you get more power and performance as a result.

However, once everything is decided and you decided upon your card, one thing remains to answered. Which PCIe slot for GPU should you use?

As a rule of thumb, putting the graphics card in the first PCIe X16 slot is the best way to get the best performance out of the card. However, in certain circumstances like when doing SLI or crossfire setup, you can use an X8 slot as well.

The reason for this has something to do with the fact that the slot is the closest to the CPU hence you get quicker data transmissions. Plus on most motherboards, the first PCIe slot IS the X16 slot.

Also Read: Best Motherboards for Photo Editing

Popular Slots for Graphics Cards

A motherboard comes with many PCIe slots. The PCIe slots, additionally, come in several different configurations that determine how many lanes you have available on the slot. The X1 has a single lane, while the X4 and X8 have four and eight lanes respectively.

The largest mainstream motherboard PCIe slot is the X16 and this one has 16 PCIe lanes.

The lanes determine the amount of bandwidth that you can achieve with a device-slot pair, and so an X16 slot will provide the most bandwidth.

A graphics card processes and generates a lot of data during operation and all this data needs to be ferried across the PCIe slots, through the PCIe lanes to the CPU.

For this, you’ll need a high bandwidth slot i.e the X16 Slot.

However, let us look at slot by slot comparison.

Also Read: What PCIe Slot Do I Have?

PCIe Slots on a motherboard
When you have many slots to choose from, finding the best-suited slot is essential. Source: tomshardware.com

The X16 Slot

This is the most preferred slot for use with a graphics card and the reason why is that since it has 16 PCIe lanes, you can transmit a lot of data in every cycle.

Most new high-performance graphics cards you can get today will require a PCIe X16 slot for optimal performance.

Many motherboards come with one or more PCIe X16 slots that can help accommodate the graphics card you will need.

When you have just one X16 slot, you always know which one you will install the card into. However, when you have more than one slot, confusion settles in.

If you have multiple X16 slots and a single graphics card, how do you go about determining the best slot for your device?

Compatibility

PCIe devices and slots are fairly cross-compatible, which means that any slot can work with any device without any outstanding issues. What it also means is that you can plug your GPU into any of the available slots and use it.

While this may be a stretch, you can always confirm that it works by unplugging your GPU from the slot it was in initially and installing it on another slot. It is supposed to work without needing any additional setup on your part.

Labeled Slots

On some motherboards, the PCIe slots are labeled so that you can easily know which slot to place your graphics card in.

On the manual, you may see one of the slots referred to as the primary slot. What this means is that you should install your GPU into this slot for the best overall performance.

Your GPU may still work when installed in any other slot, however, it will work best if you plug it into the primary slot if one has already been specified.

Which PCIe slot for GPU
Some high-end graphics cards like the RTX 2080 are best used in an X16 Slot. Source: wccftech.com

The X8 Slot

Under some circumstances where the X16 slot is unavailable or damaged, your next best option for a GPU will be the X8 slot.

X8 Slot is also the option to go for when you are doing an NVIDIA SLI or AMD Crossfire build on mainstream computers. More on this below.

With an X8 slot, however, you get significantly reduced bandwidth, it is effectively halved when you step down from an X16 slot to an X8 slot in the same PCIe generation.

Before you get all worked up, here’s some good news. Stepping down from an X16 to an X8 slot, you don’t get half the performance despite the amount of bandwidth lost. You’ll only end up with just a few less FPSs as you would have if you were running it in an X16 slot.

For more clarity, some tests have shown that using the X16 slot over the X8 one will only give you about 2% more performance in many cases.

With this in mind, you can rest easy that for most casual gamers, using an X8 slot for your GPU will work just fine, maybe not as good as an X16 but the games will still be playable.

Slot Labeling

A lot of the time, the X8 slot will be labeled as a secondary slot meaning that it’s meant to be used in situations where the primary slot can’t be used or when you’re installing multiple GPUs and only have one X16 slot.

SLI and Crossfire

Chances are you have heard of these two terms being thrown around at one time or another. They are both used to accomplish the same thing though; allow a multi-GPU stack to run as a more powerful single-GPU setup.

SLI is offered by NVIDIA whereas AMD offers the alternative, Crossfire. They accomplish their tasks differently, but to the user, all you need to know for now is that you’ll need at least two graphics cards and they will need to work in unison to effectively boost your PC’s GPU performance.

Now when it comes to installing two cards on an average mainstream computer, you need at least two PCIe slot with the physical size of an X16 slot.

When installing two cards, generally the the first PCIe X16 slot dials down its bandwidth to X8 and the second PCIe X16 sized slot already operates at X8 mode.

Also Read: 5 Best Motherboards for SLI in 2020

A motherboard configured for SLI
With enough PCIe lanes and SLI support, you can build a system like the one above for better performance. Source: extremetech.com

The X4 and X1 Slots

Right off these slots should be avoided for GPUs. Not only are they significantly smaller in size than the GPU’s full-length connector, but they also have the lowest bandwidths you can expect on a motherboard’s PCIe slot.

PCIe X4 and X1 slots are very useful for certain things, however, when you need to carry the large amounts of data generated between a CPU and a GPU, you may encounter some noticeable performance drops.

Additionally, not many people would consider using an X4 slot for the GPU if they are planning on playing some hardcore games at high resolutions and with high FPSs.

In rare instances when doing three-way AMD Crossfire, for instance, you can install the third AMD GPU on the X4 slot.

Also Read: What are PCIe X1 Slots Used For?

Which PCIe Slot for GPU

Getting down the main agenda, the GPU will best be served if it can be connected to the fastest slot, in this case, an available X16 slot. However, it will still work when connected to an X8 slot.

But, the best option is X16.

Conclusion

Just about any PCIe slot on your motherboard can accommodate and work with a GPU. However, not all slots are equal. And, when deciding which PCIe slot for GPU, you will need to choose one that has the best to offer.

Enter the X16 slot. This slot is fast and large enough to accommodate most of the user-grade GPUs available in the market.

Its performance lets you make use of your card as it provides a lot of bandwidth for the transfer of large amounts of data in just a short time. You can also use the X8 slot but should not be the primary choice.

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