AMD Radeon RX 6500XT performance likely to be visibly limited on PCIe Gen3 platforms

Published: 17th Jan 2022, 12:07 GMT   Comments

AMD Radeon RX 5500XT 4GB tested on PCIe Gen4 x8 is 49% faster on average compared to Gen3 x4

HardwareUnboxed is investigating a potential problem with the upcoming ‘entry-level’ Radeon card that is due to come out in just 2 days. 

As we reported earlier, the Radeon RX 6500XT graphics card will feature a limited PCIe Express interface to four lanes. The card is based on the fourth generation of PCI Express which means that four lanes should provide just as much bandwidth as eight lanes on Gen3 standard.

This might not immediately appear as an issue, however, for the budget GPU such as RX 6500XT, chances are that many users considering this card may still feature PCIe Gen3 system, which means even less bandwidth with only four lanes available.

[Hardware Unboxed] Will PCIe x4 Cripple the Radeon 6500 XT? PCIe Bandwidth Test (108,682 views)

It should be noted that HardwareUnboxed is not allowed to post their RX 6500XT testing results just yet due to the review embargo, but they can use previous-gen models such as Radeon RX 5500XT based on Navi 14 GPU to see if there is any performance bottleneck coming from the Gen3 interface.

As noted by the reviewer, bandwidth issues are more likely to be expected on 4GB cards, rather than 8GB, simply because some resources will be stored in the video memory, rather than being constantly pulled from system memory or storage. The RX 5500 XT was available in two variants, featuring either 8GB or 4GB memory, which makes it a perfect candidate for this type of test.

Examples of AMD Radeon RX 5500XT being bandwidth-constrained on PCIe Gen3 interface, Source: HardwareUnboxed

The results have shown that games that were already affected by limited VRAM of the graphics card were more likely to show double-digit performance impact from the bandwidth-constrained interface. The conclusion is that PCIe 3.0 x4 will reduce the average framerate at 1080p resolution. The Gen4 x8 (which is a default configuration of the RX 5500XT) will be 49% faster than Gen3 x4. Unfortunately, there was no graph for the PCIe 4.0 x4 vs 3.0 x4.

AMD Radeon RX 5500XT PCIe Gen3 x4 vs Gen4 x8, Source: HardwareUnboxed

It should be mentioned that RX 6500XT is based on newer RDNA2 architecture and comes with 16MB of Infinity Cache. Both upgrades could mitigate the bandwidth problem to some degree, however, they are not expected to have a significant impact. HardwareUnboxed will include PCI Express testing to their upcoming RX 6500XT review so make sure to check it out in 2 days.

AMD Radeon RX 6000 Series
VideoCardzRX 6600 XTRX 6600RX 6500 XTRX 5500 XT
Architecture7nm RDNA27nm RDNA26nm RDNA27nm RDNA
GPUNavi 23 XTNavi 23 XLNavi 24 XTNavi 14 XTX
Infinity Cache
32 MB
32 MB
16 MB
Ray Accelerators
Game Clock
2359 MHz
2044 MHz
2610 MHz
1717 MHz
Boost Clock
2589 MHz
2491 MHz
2815 MHz
1845 MHz
Memory Clock
16 Gbps
14 Gbps
18 Gbps
14 Gbps
4/8 GB GDDR6
Memory Bus
256 GB/s
224 GB/s
144 GB/s
224 GB/s
PCI ExpressGen4 x8Gen4 x8Gen4 x4Gen4 x8
379 USD
329 USD
199 USD
169 USD
Launch DateAugust 2021October 2021January 2022December 2019

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