NVIDIA RTX 30 series and the NVIDIA RTX 40 series graphics cards are some of the few rare devices that actually utilize the PCIe 4.0 protocol.
Not many devices use the newer 4.0 standard at the moment mostly because the majority of the PCs and their motherboards out there still conform to the older PCIe 3.0 generation.
Hence, this begs the question, will RTX 30 and 40 work in PCIe 3.0?
The simple answer to the question is a yes, both the RTX 30 and 40 series graphics card WILL work in the older PCIe 3.0 slot, albeit, with a marginal performance drop.
In the following text, I will explain PCIe protocol in general and also talk about whether you can use RTX 30 and the RTX 40 on the older slots.
PCIe Version and Speeds
PCIe protocol essentially comprises of data channels known as PCIe lanes. These lanes carry the information to and from the devices attached to the PCIe slots.
Now not all slots have an equal amount of PCIe lanes. Some have a higher and other have a lower amount of PCIe lanes.
An x16 slot ideally has 16 lanes. An x1 slot has one PCIe lane.
The overall bandwidth or the amount of data a PCIe slot can carry depends upon two characteristics:
- The amount of PCIe Lanes a Slot has
- The version of the PCIe Lanes
The bandwidth a slot can carry scales with the amount of lanes. So a slot with 4 x PCIe lanes would have twice the data carrying capacity as compared to a slot with one PCIe lane.
In addition to that the version of the PCIe slot has a direct impact on the per lane data transfer rate. So much so that with each newer generation, the amount of data each lane can carry doubles.
As such, while 1 x PCIe 3.0 lane can carry 0.985 GB/s data, 1 x PCIe 4.0 lane can carry twice as much data ie 1.969 GB/s.
With each newer version of PCIe, new devices are made that can leverage the higher bandwidth.
For instance, we have the Gen 4 NVMe SSDs such as the Samsung 980 Pro. These can reach speeds of upto 5500 MB/s. Compare this to Gen 3 NVMe SSDs which maxed out at 3500 MB/s transfer rate.
Newer PCIe Generations Give Birth to New Gen Graphics Card
Similarly, with each newer PCIe generation, we get new top of the line graphics cards that tend to leverage the higher bandwidth.
NVIDIA RTX 30 and 40 series graphics cards are some of the rare devices that actually do utilize the newer PCIe 4.0 protocol.
A graphics card is generally a PCIe device that generates the most amount of data. As such, it requires the largest slot available on any motherboard, the x16 slot with 16 PCIe lanes.
However, the point worth noting here is that while a PCIe 3.0 x16 slot can carry a maximum of 15.754 GB/s, PCIe 4.0 x16 slot can carry 31.508 GB/s of data.
So in other words, if a graphics card were to generate data at a higher rate than 15.754 GB/s, then a PCIe 3.0 slot would act as a bottleneck.
Now NVIDIA RTX 30 and 40 graphics card most certainly have the potential to generate a higher data, and as such the PCIe 3.0 slot would act as a bottleneck to their performance.
How much of a performance drop can you if put a RTX 30 and 40 on a PCIe 3.0? Read on.
Performance Impact of PCIe 4.0 Graphics Card on a PCIe 3.0 Slot
Puget Systems has done a comprehensive study on this whereby they tested Titan RTX 24 GB PCIe 3.0 GPU and RTX 3090 24 GB PCIe 4.0 GPU on version 1, 2, 3, and 4 PCIe x16 slot.
They tested on several software and benchmarks. The results revealed that while there is certainly an impact, it actually depends upon the software you use or the activity you perform.
Image: PugetSystems.com. Comparison of how RTX 3090 and Titan RTX perform on different PCIe generations. A significant impact can be seen on performance in DaVinci Resolve (video editing software) when using the cards in older PCIe slots.
Running a PCIe 4.0 RTX 3090 on older Gen 3.0, 2.0 and 1.0 slots resulted in performance drop on DaVinci Resolve.
On a PCIe 4.0, the RTX 3090 scored 156 points. The same card on a PCIe 3.0 scored 150.
In addition to that, for future reference you can also see that running a PCIe 3.0 device on a 4.0 slot would not give you any performance boost. For instance the PCIe 3.0 Titan RTX scored 109 on both PCIe 4.0 and PCIe 3.0 slots.
Again as mentioned, the results were not typical across the board. For instance, the results on the OctaneBench were quite inconclusive and there was no visible impact of using a PCIe 4.0 on older slots.
So basically, the impact of using an RTX 30 or 40 on PCIe 3.0 slots can vary depending upon the application you run.
PugetSystems summarizes this well:
For applications where data is constantly traveling across the PCI-Express bus, we can see that the generational bandwidth differences do have a very measurable impact on real-world performance.
Impact on Games When Using RTX 30 on PCIe 3.0
GamersNexus.net has done a comprehensive study on the impact of using an NVIDIA RTX 30 graphics card, the RTX 3080, on PCIe 4.0 and 3.0 slots by testing various games.
I recommend having a look at the entire video here:
Basically, the gist of the discussion here is that while there is certainly a difference, it is not noticeable enough.
Take for instance GTA V. The difference PCIe 4.0 and 3.0 makes in the average frame rates is of only 2 frames! Which is quite negligible.
Source: Gamers Nexus
So Will RTX 30 and 40 Work in PCIe 3.0?
So this brings us back to our original question, will RTX 30 and 40 work in PCIe 3.0 slots?
Yes, a PCIe 4.0 device such as the NVIDIA RTX 3000 and 4000 series graphics CAN work in a PCIe 3.0 slot. However, you may see a marginal performance drop in doing so.
PCIe protocol is both backward and forward compatible. Meaning, a PCIe 4.0 device can be used in the older 3.0 or even 2.0 slots. Likewise, a PCIe 2.0 or a 3.0 device can also be used in a PCIe 4.0 slot.
However, the bottlenecks when using a newer Gen device in an older Gen slot are real.
So to summarize, the answer to the question “will RTX 30 and 40 work in PCIe 3.0 slots?” is a yes since PCIe protocol is backwards compatible.
However, you may see a small performance drop.