The PCIe interface and available lanes are two very important keys because they determine the bandwidth available to the graphics card and because this is something that can ultimately affect its performance. In TechPowerUp they published a new article where measure PCIe scaling with GeForce RTX 4090 using different configurations and games and the results they achieved are very interesting.

Before we continue, let’s see how this standard works to better understand the results of PCIe scaling with the GeForce RTX 4090. The PCIe standard used, which can be first, second, third, fourth or fifth generationdetermines the available bandwidth of the component we connected, in this case the graphics card, for each available line.

• PCIe Gen1 x1: 250 MB/s.
• PCIe Gen2 x1: 500 MB/s.
• PCIe Gen3 x1: 984 MB/s
• PCIe Gen4 x1: 1969 MB/s.
• PCIe Gen5 x1: 3938 MB/s.

Based on what we just saw, a PCIe Gen1 x16 interface (16 lanes) would have a total bandwidth of 4 GB/swhile a PCIe Gen5 x16 interface (16 lanes) would have the bandwidth 63.02 GB/s You can calculate the total bandwidth by multiplying the base I gave you by the total number of lines.

PCIe scaling with GeForce RTX 4090: when does performance drop?

As we just saw, with the newer PCIe standard we need fewer lanes to achieve higher bandwidth, and the differences can be huge. However, in terms of performance, the reality is that even with a graphics card as powerful as the GeForce RTX 4090, we cannot saturate the PCIe Gen 4 x16 interface because the difference between this interface and the PCIe Gen3 x16 interface is only 1%.

Interestingly, when we switch to PCIe Gen2 x16, the difference in performance is very small we lose barely 3% compared to PCIe Gen 3., and it wasn’t until we got off that that we started seeing a sharp drop in performance. This confirms that there is still no need to use the PCIe Gen5 interface to connect the graphics card and that it will not improve performance.

We see this when we do an individualized analysis by games Gears 5 is one of the ones to suffer the most from the drop from PCIe Gen3 x16 to PCIe Gen2 x16. Only on the other side of the coin would we have Far Cry 5, which is one of the games that suffers the least from the change to a lower standard. Keep in mind that this is also one of the oldest games in comparison.

These results allow us to clarify From what bandwidth will we be bottlenecked if we use GeForce RTX 4090because we can calculate it starting from PCIe Gen2 x16 interface, which is the level at which the performance loss starts to be noticeable, even if it is small.

This calculation confirms it when dropping to 8GB/s it said the graphics card wouldn’t have enough bandwidth develop its full potential, which would be equivalent to PCIe Gen4 x4 in a more modern standard.