Radeon RX 5500 XT, PCI Express 3.0 castrates performance?

With the release of Radeon RX 5500 XT, AMD has added a new piece to complete its offer of video cards based on the Navi project.

The video card is available with 4 and 8 GB of memory, but as seen in some tests carried out both internally and from other sites, iIn some games, less memory reduces performance: the 4 GB are starting to become few and for this reason we suggest to aim for the 8 GB in the future. Apparently there is more.

The German portal PCGamesHardware has tried both variants by configuring them both in PCI Express 3.0 (on a platform with Core i9-9900K) than in PCI Express 4.0 (X570 / Ryzen 5 3600), discovering an interesting detail. They recognized that when the 4 GB of VRAM becomes full, using the card on a PCIe 4.0 platform improves performance.

The 8 GB video card instead reported less marked improvements from PCIe 3.0 to 4.0, and clearly it is the 4 GB more that weighs more on the final frame rate.

Why is this happening? When the VRAM is full, the extra data is sent via the PCIe bus to the RAM. The higher the bus speed, the faster this data exchange takes place and there are no delays in playing the next frame.

The RX 5500 XT, although inserted in a PCIe x16 slot, works at most in PCIe 4.0 x8, which guarantees a theoretical bandwidth similar to a PCIe 3.0 x16 interface.

AMD said that a GPU in this segment has eight bandwidth guaranteed PCI Express lines, which is correct, but apparently games that require a lot of memory undermine the interface.

PCGamesHardware tests have shown that performance halves in memory read and write operations. Where a PCIe 4.0 x8 can reach a transfer rate of 12.5 GB / s, the PCIe 3.0 x8 stops at 6.5-6.7 GB / s.

What do these data mean? The improvements vary according to the title and the parameters set; the 4 GB RX 5500 XT benefits from the increased bandwidth guaranteed by the new interconnection, especially in Assassin’s Creed, Far Cry and Wolfenstein Youngblood. The 8 GB variant however did not show any major improvements.

Overall, the choice of AMD to connect this card in x8 mode can be defined as curious, especially the 4 GB version, which has more possibilities to occupy VRAM to the maximum.

Obviously not all titles will be affected by the limits of VRAM, but it still remains a handicap for future games and in part for current ones.

Those who have a Radeon RX 5700/5700 XT do not have to worry too much about any performance differences of the cards in PCIe 3.0 x16 and 4.0 x16.