Introduction

NVIDIA today released the GeForce RTX 3080 "Ampere" graphics card, its first gaming-segment graphics card to implement PCI-Express Gen 4.0 bus support. Be sure to check out our main review of the GeForce RTX 3080 Founders Edition, where we go into many more details about the card. The new interface doubles bandwidth over PCI-Express Gen 3.0, enabling 64 GB/s of bi-directional bandwidth (or 32 GB/s per direction). The per-direction metric is more relevant because compared to a storage device, such as an SSD, data moves more in one direction (from the CPU to the GPU) than the other.



Back in July 2019, the first PC platform implementing PCI-Express Gen 4.0 debuted with AMD's 3rd Gen Ryzen platform, along with the company's RX 5700 XT "Navi." NVIDIA is a good 14 months behind AMD at implementing PCI-Express Gen 4.0, but the RTX 3080 "Ampere" being launched today is the first enthusiast-segment card supporting PCIe Gen 4, which NVIDIA markets as being capable of 4K UHD gaming, and hence commonsense guides us to think it's better positioned to utilize the higher interface bandwidth. To highlight this, we did a similar PCIe scaling article with the RX 5700 XT last year and found the performance impact of PCIe Gen 4 to be negligible.

There's another reason we feel the RTX 30 series is better positioned to benefit from PCIe Gen 4, and that is RTX-IO, a feature which leverages DirectStorage to transfer compressed data directly from your SSD onto the graphics memory, de-compressing using GPU hardware, with negligible CPU overhead. With PCIe Gen 4-based M.2 NVMe SSDs enabling compressed data streams at up to 7 GB/s, PCIe Gen 4 should in theory reduce the system bus bandwidth impact of RTX-IO on the RTX 3080.


As we mentioned earlier, AMD has had PCIe Gen 4-based desktop and HEDT platforms since July 2019, and the 11th Gen Core "Rocket Lake" desktop processor is rumored to finally bring PCIe Gen 4 support. Some Intel Socket LGA1200 motherboards are already shipping with preparation for PCIe Gen 4. With NVIDIA's RTX 30 series implementing PCIe Gen 4, the standard could hit critical mass. Are you still on an older Intel or AMD platform? Don't worry, the RTX 3080 supports older PCIe generations, it will automatically fall back to the fastest interface speed available.


Since 3rd Gen Ryzen is the only desktop processor series with PCIe Gen 4 as of this writing, we decided to put together a special test-bench for this article, powered by an AMD Ryzen 9 3900XT 12-core processor and an ASRock X570 Taichi motherboard. On this platform, we test the performance impact of not just older generations of PCIe, but also fewer lanes within a PCIe generation. We use the motherboard BIOS settings to limit PCIe generations, while PCIe lane counts are reduced using a physical barrier (duct tape that seals off individual PCIe lane contacts), letting us toggle between x16 and x8. The RTX 3080 is put through our entire selection of games, which should highlight how each title responds to the new bus standard.

In a separate article, we compared the Ryzen 9 3900XT to the Core i9-10900K with the maximum PCIe bandwidth each of the two processors supports.