PCIe stands for Peripheral Component Interconnect Express. Like SATA, it is an interface technology that is used to connect the motherboard with other PC components like graphics cards and SSDs. It consists of multiple channels, known as lanes, that offer extremely high data transfer rates. Knowing about the version and number of PCIe lanes is very important in order to make the best use of your graphics card and to allow you to upgrade your system down the road, should you so desire.
How Many PCIe Lanes Does a Graphics Card Use
If you are like me, chances are you have spent a considerable amount of time banging your head trying to make sense of all these terms like PCIe version number, slot size, or whatever those “x8”s and “x16”s mean. Before we delve into the main article, let’s have a look at what each of these terms mean so that, hopefully, by the end of the article, you don’t feel more confused than you already are. So, without further ado, let’s get right into it.
PCIe slots are where you plug your external component in. You might have noticed the the numbers x16 or x8 in discussions involving PCI Express. These refer to the number of lanes a particular slot has, something we will discuss next. It is possible that two slots might look physically identical but actually have a different number of lanes. This can be observed in two ways.
The first one is fairly straightforward as you can directly see an “x8” or “x16” written right next to the PCIe slot in fine print, indicating the number of lanes the particular slot has.
The second one involves looking at the number of electrical pins a slot has. This requires you to carefully look from a particular angle at the slots. An x8 slot will have a fewer number of electrical pins even though it might look physically indistinguishable from an x16 slot on the outset.
What we discussed above are special cases. In general, however, the physical size of the slot corresponds to the number of lanes it has, and hence an x4 slot would be typically noticeable smaller than an x16 slot.
Lanes are the channels that the PCIe interface uses for linking your graphics card to the motherboard. Each lane consists of two pairs of wires for transmission and reception of data. Some lanes are connected directly to the CPU while others are connected to the motherboard. These often stem from the topmost slot of the motherboard. The lanes connected to the CPU are the highest in number and hence offer the highest bandwidth.
Lanes can be thought of as two-way roads that link two cities. The cities in our context are the motherboard (or CPU) and the GPU. Just as more roads mean more vehicles can simultaneously travel, more lanes mean more data can be transferred. This means that even if the data transfer rate on a typical lane is slow, the fact that there are a 8 or 16 (i.e. x8 or x16) of them means that the overall data transfer rate is still very high.
While lanes can be thought of as highways, PCIe version number can roughly be viewed as an indication of the speed at which each vehicle is moving on a lane. The higher the number, the faster the speed. Thus, version number is another way by which the overall data transfer rates have improved. Each version number increase doubles the data transfer speed over the preceding version for the same slot size.
For example, let’s consider different versions of the x16 slot. In 2003, the PCIe x16 Version 1 was released. It supported a maximum data transfer rate of 4 GB/s. A few years later, in 2007, Version 2 was released. This supported a maximum speed of 8 GB/s. Then came the Version 3, which allowed data transfer rates of up to 15.75 GB/s. This trend has been going on and right now, as of 2023, Version 6 has been released which supports a maximum data transfer rate of a whopping 126 GB/s.
PCIe lanes and your GPU
Compatibility is generally not an issue when it comes to PCIe slots. So, for example, a PCIe Version 3 based card can be plugged into a PCIe Version 4 based slot, and and a PCIe Version 4 based card can be plugged into a PCIe Version 3 based slot. However, the data transfer rates will be limited by the speed at which the slower one of the two components operates. This means that processing power and its utilization is a more important factor when choosing the slot into which you want to plug your GPU, which we discuss next.
How powerful your GPU is?
The number of lanes a GPU uses is roughly proportional to how powerful the card itself is. Lower power cards generally make use of lower number of lanes. They can be plugged into an x16 or x8 slot and should would work just fine in both of them. Nvidia’s GT 710 is one example of such a card.
However, if you own one of those RTX behemoths, the maximum potential of your graphics card will be significantly undercut if you plug it into an x8 slot, even if it is compatible with it. So, generally speaking, you should plug your GPU into the x16 slot.
Number of GPUs
If you have a single GPU, things are simple and you can simply plug it into the slot with the highest number of lanes. However, when you use multiple GPUs you have to make use of the slots with lower number of lanes too. To keep things in harmony, both cards can only make use of the lower number of lanes. For example, both cards will only make use of 8 lanes even if one of them is plugged into the slot that has 16 lanes.
As a result, the overall processing power is slightly lower than the sum of the individual processing powers of each graphics card. However, the use of multiple GPUs for consumer grade PCs has become obsolete in recent times mainly because even the individual cards themselves are so sufficiently powerful that they make the addition of another graphics card unnecessary.
So back to our original question: how many PCIe lanes does a GPU use? The answer is it depends. The main controlling factors being how powerful your GPU is and how many GPUs you are using. Most motherboards contain at least one x16 slot. So, if you use a single card, the limiting factor is going to be the number of lanes the card itself can support. If you want to use multiple cards, make sure to find a suitable motherboard that has extra slots for each card.
In most instances, however, at least in recent times, a GPU makes use of 16 lanes to provide optimal performance, and the only thing you need to remember is to plug your GPU in the x16 slot to get the most out of it.