Resource TechPowerUp recently tested a new graphics adapter AMD Radeon RX 6400 on legacy interface PCIe 3.0to measure performance drops compared to PCIe 4.0, and it turned out that this stems from the unorthodox GPU configuration adapted for four PCIe lanes. The average performance drop was more than 14%, depending on the resolution.
AMD Radeon RX 6400 – entry-level graphics accelerator for the desktop segment with a core Navi 24 from AMD, originally designed for laptops, like its older brother, the Radeon RX 6500 XT. This GPU contains only four PCIe 4.0 lanes as a measure to reduce manufacturing costs.
The Radeon RX 6400 has a rough reduction in core count and memory bandwidth by thirteen% compared to the Radeon RX 6500 XT. The video card has only 768 cores and 128 Gbps memory bandwidth by reducing GDDR6 speeds to 16Gbps. However, the amount of memory remains unchanged at the level 4 GB. But the main strength of the Radeon RX 6400 is power consumption, it has half the power of the Radeon RX 6500 XT 53W, which makes this GPU very useful in small budget systems that cannot power higher-end GPUs with an auxiliary power cable.
24 games were tested and the Radeon RX 6400 running on the PCIe 3.0 bus saw an average performance drop of 14%. 1080P so with 1440p compared to PCIe 4.0. 4K results were even worse, with a 23% performance gap. However, this will undoubtedly make a big difference, as the Radeon RX 6400 offers unplayable FPS on any PCIe generation.
Some of the worst results included a racing simulator F1 2021 and shooter Doom Eternal, in which the difference in performance reached 79% and 43% at 1080P. Luckily, almost every other title we tested was in the 14% range or below, but these two games show just how intense some game engines using PCIe can get.
Testing of the Radeon RX 6500 XT showed a performance gap of 13% for PCIe 3.0 vs. PCIe 4.0. The Radeon RX 6400 cannot escape Navi 24’s four-lane limitations, even if the GPU itself is slower. PCIe 3.0 Radeon RX 6400 was almost on 20% slower than the GeForce GTX 1650, which runs on the same PCIe 3.0 interface and a much more optimal x16 lane configuration. However, when installed in a PCIe 4.0 interface, the Radeon RX 6400 performs similarly to the GeForce GTX 1650.
Consumers opting for the Radeon RX 6400 need a PCIe 4.0 platform to avoid the severe performance penalty from the PCIe 3.0 bus. The biggest problem is that most systems are still on PCIe 3.0 and gamers who are likely to buy a Radeon RX 6400 are running it on an older system. If you don’t have PCIe4.0 the best alternative is GeForce GTX 1650 from Nvidia or even older Radeon RX 570which is faster than the Radeon RX 6400 and does not require PCIe 4.0 to unlock its full performance.