TechPowerUp recently tested AMD's new Radeon RX 6400 GPU on the slower PCIe 3.0 interface to measure any substantial drops in performance compared to PCIe 4.0 and found that to be the case thanks to the GPU's unorthodox configuration of just four PCIe lanes. On average, performance drop-offs were upwards of 14%, depending on the resolution.
AMD's Radeon RX 6400 is the company's newest entry-level GPU for the desktop market featuring AMD's super tiny Navi 24 die, initially for laptops. Like its bigger brother, the Radeon RX 6500 XT, this GPU only packs four PCIe 4.0 lanes as a measure to cut down costs. The Radeon RX 6400 features a rough 13% reduction in core count and memory bandwidth compared to the Radeon RX 6500 XT. The graphics card has just 768 cores and 128 GBps of memory bandwidth, thanks to a reduction in GDDR6 speeds to 16 Gbps. However, memory capacity stays the same at 4GB. But the Radeon RX 6400's main strength is its power consumption. It has half the Radeon RX 6500 XT power draw for 53W, making this GPU very useful in small systems budget systems that cannot power higher-end GPUs with auxiliary power.
In the 24 games, TechPowerUp tested, the Radeon RX 6400 running on PCIe 3.0 averaged a 14% decrease in performance at both 1080P and 1440P cumulatively compared to PCIe 4.0. 4K results were even worse, with a 23% deficit in performance. However, we doubt it'll matter much since the Radeon RX 6400 offers unplayable FPS on either PCIe generation.
Some of the worst offenders included F1 2021 and Doom Eternal, which saw a 79% and 43% difference in performance at 1080P. Thankfully, almost all other titles tested were in the 14% range or lower, but these two games specifically show how truly PCIe bandwidth-intensive some game engines can become.
TechPowerUp's testing for the Radeon RX 6500 XT showed nearly the same results, showing a 13% deficit in performance for PCIe 3.0 vs. PCIe 4.0. The Radeon RX 6400 can't escape Navi 24's four-lane limitations, even if the GPU itself is slower. The Radeon RX 6400's PCIe 3.0 was almost 20% slower than GeForce GTX 1650, which operates on the same PCIe 3.0 interface and runs on a much healthier x16 lane configuration. However, when installed on a PCIe 4.0 interface, the Radeon RX 6400 performed similarly to the GeForce GTX 1650.
Consumers eyeing the Radeon RX 6400 need a PCIe 4.0 platform to avoid the severe performance drop-off from PCIe 3.0. The biggest issue is that most systems are still on PCIe 3.0, and the consumers that are likely to buy a Radeon RX 6400 are on an old system. If you don't have access to PCIe 4.0, the better alternative is Nvidia's GeForce GTX 1650 or even the more senior Radeon RX 570, which is faster than the Radeon RX 6400 and doesn't require PCIe 4.0 to unlock its full performance.