Introduction

Today, we are testing the performance impact of PCI-Express Gen 3 on the entry-level Radeon RX 6400 graphics card, which we reviewed last week. Until a few generations ago, the notion that PCI-Express bandwidth is limiting the performance of an entry-level graphics card would've come across as absurd, but times are changing. Recently, GPU vendors have been lowering the PCI-Express lane count of their entry-mainstream GPUs in a bid to lower the pin-count and reduce traces on the PCB.



For the Radeon RX 6400, this means a PCI-Express 4.0 x4 bus interface—bandwidth comparable to PCIe 3.0 x8 or PCIe 2.0 x16. By itself, PCI-Express 4.0 x4 seems like plenty of bandwidth, 8 GB/s per direction, until you realize that you also need a PCIe Gen 4.0 capable processor and motherboard to use it in Gen 4 mode—that's Ryzen 3000 Matisse, Ryzen 5000 Vermeer, Core Rocket Lake, and Core Alder Lake. Entry-level parts from both brands are relegated to PCI-Express Gen 3.0.

If you're experiencing déjà vu, it's because we recently tested PCI-Express scaling of the RX 6500 XT, the slightly bigger sibling of the RX 6400, and drew some interesting conclusions, mainly that PCI-Express Gen 3 bites off a big chunk of performance. In my RX 6400 review, I suggested that the performance hit would be roughly similar, but several readers requested I actually test this theory, so here we are. We are hence testing the RX 6400 in PCI-Express Gen 3 mode, and evaluating its performance loss to Gen 4 to see just how much it affects the target audience of the RX 6400: those with entry-level platforms that have PCI-Express Gen 3.

Test System

Benchmark scores in other reviews are only comparable when this exact same configuration is used.

• All games and cards are tested with the drivers listed above—no performance results were recycled between test systems. Only this exact system with exactly the same configuration is used.
• All graphics cards are tested using the same game version.
• All games are set to their highest quality setting unless indicated otherwise.
• AA and AF are applied via in-game settings, not via the driver's control panel.
• Before starting measurements, we heat up the card for each test to ensure a steady state is tested. This ensures that the card won't boost to unrealistically high clocks for only a few seconds until it heats up, as that doesn't represent prolonged gameplay.

Each game is tested at these screen resolutions:

• 1920x1080: Most popular monitor resolution.
• 2560x1440: Intermediary resolution between Full HD and 4K, with reasonable performance requirements.
• 3840x2160: 4K Ultra HD resolution, available on the latest high-end monitors.

Assassin's Creed Valhalla

Released: 2020 — API: DirectX 12 — Engine: AnvilNext 2.0

It is the year 873 AD, the most violent period in Norwegian history. A Viking clan leader takes a group of refugee warriors across the seas to medieval England, where they set up camp as barely welcome migrants to the local kingdoms. You form alliances with local lords and raid Saxon strongholds for resources to build and grow your settlement. The historic cities of Winchester, London, and York, as well as vast landscapes of Norway, are brought to life in this outstanding Assassin's Creed experience.

Battlefield V

Released: 2018 — API: DirectX 11 — Engine: Frostbite

Battlefield V is the latest chapter in EA's smash-hit online multiplayer shooter franchise. The series has come full circle since its debut "1942" and is set in World War II. The single-player campaign is broken up into bite-sized chunks called War Stories. Much like Battlefield 1, each depicts a different theater of war, a different protagonist, and a different mission. The multi-player builds on the franchise's core strengths with the addition of new game modes and room for a future mode rivaling battle royale.