PCIe 3.0 vs. 4.0 tested in games

– Navi graphics cards from AMD support PCIe 4.0. And that can be an advantage over the older PCI 3.0 standard. As the test shows, a special criterion has to be met. If this is not the case, there are (still) no disadvantages with the classic PCIe 3.0 system.

AMD Navi can PCIe 4.0

AMD's Navi generation represents the first graphics cards on the market to support PCIe 4.0 in combination with a Ryzen 3000 processor based on Zen 2 and an X570 mainboard. In the past few weeks, more and more reports have appeared on the Internet that the Radeons with PCIe 4.0 have assumed better performance than with PCIe 3.0. In a first, if somewhat older test by the editors, this had not yet been shown.

A lot has happened since October 2019. There are new Windows versions, drivers and games, but above all significantly more navigation graphics cards that are configured differently. There are the classic models with 8 GB memory and 16 PCIe lanes (Radeon RX 5700 series), copies with 6 GB and 16 lanes (Radeon RX 5600 XT) as well as variants with only 8 lanes and either 4 or 8 GB ( Radeon RX 5500 XT). So there are many factors that can influence the proof of a benefit of PCIe 4.0. Does memory play the main role?

To find out, BitcoinMinersHashrate used several AMD graphics cards, games and two detail settings in this test. The answer to the question of whether a doubled bandwidth via the PCIe slot (PCIe 4.0 can transfer just under 32 GB / s with 16 lanes instead of around 16 GB / s with PCIe 3.0) is only sought if there is a lack of memory or in general can be.

The graphics cards, PCIe lanes and memory

For this test, the editors used the Radeon RX 5700, the Radeon RX 5600 XT and the Radeon RX 5500 XT, which all work according to AMD's reference information. The Radeon RX 5700 is an old friend: It offers 8 GB of memory and 16 PCIe 4.0 lanes.

The Radeon RX 5600 XT is the latest addition to the Navi family and represents a premiere for AMD, because the graphics card does not use a 4 GB or 8 GB frame buffer, but offers exactly the middle ground with 6 GB. There are no differences in the PCIe lanes: The Navi 10 GPU also comes with 16 PCIe lanes according to the new 4.0 standard.

The third in the group is the Radeon RX 5500 XT. The graphics card is available with 4 and 8 GB, both versions are used for the test. In contrast, the red pencil was used for the PCIe lanes. PCIe 4.0 is still supported, but instead of the full 16 lanes there are only 8. With 8 lanes at PCIe 4.0 speed, the bandwidth is just as high as with 16 lanes of type 3.0.

The test system and the games used

The Core i9-9900K otherwise used in graphics card tests could not be used for this article because Intel does not yet support PCIe 4.0. Instead, a Ryzen 7 3700X was used, which was used on an MSI MEG X570 Godlike with the eponymous X570 chipset that is decisive for PCIe 4.0. A 16 GB RAM (DDR4-3200, 14-14-14-32) and a freshly installed Windows 10 1909 together with all updates were further important components of the system. Adrenaline 20.1.4 was installed as the driver.

Four games take part in this comparison, three of which have been explicitly selected due to their known high memory consumption. It should therefore be borne in mind that the test results do not represent a cut through the entirety of all games that can be transferred in any way to the normal performance rating.

Almost 8 GB in worst-case scenario

The games are Call of Duty: Modern Warfare, F1 2019, Ghost Recon Breakpoint and Shadow of the Tomb Raider. F1 2019 addresses up to 5.3 GB of memory in 1,920 × 1,080 with maximum details in the test sequence. It is 6.3 GB in Shadow of the Tomb Raider, 7 GB in CoD and 7.5 GB in Breakpoint. Speaking of Full HD: This is the resolution that is used in this test, because the Radeon RX 5500 XT and the Radeon RX 5600 XT feel at home there.

In addition to the maximum level of detail, a second run with minimized texture details was carried out – all other graphics settings are unchanged. In this way it can be found out whether PCIe 4.0 can also bring advantages beyond the lack of memory. This is because less than 4 GB of memory is addressed for all four titles, so that the memory size can no longer influence the results.

Benchmarks in 1,920 × 1,080

When measuring the frame times, the differences between the different memory configurations and PCIe bandwidths can be quickly recognized.

If the memory runs out, PCIe 4.0 is an advantage

In the case of the Radeon RX 5500 XT with 4 GB, PCIe 4.0 can bring a big advantage for games that require more than 4 GB of graphics card memory. On average, the frame times of the graphics card increase by 19 percent compared to PCIe 3.0. The Radeon RX 5500 XT with 8 GB, on the other hand, shows a completely different behavior, with PCIe 4.0 the model only grows by 2 percent. Three insights can already be derived from this.

• In the performance class of the Radeon RX 5500 XT, more than 16 GB / s bandwidth via the PCIe slot are not an advantage, PCIe 4.0 x8 (as chosen by AMD) or alternatively PCIe 3.0 x16 are sufficient.
• If the game demands more graphics memory than the graphics card offers, only 8 GB / s via the PCIe slot (like PCIe 3.0 x8 offers) means an additional loss of performance compared to the installation of too little graphics memory and 16 GB / s via the PCIe Slot (as PCIe 4.0 x8 offers).
• However, there is still a loss of performance. More bandwidth via the PCIe slot or PCIe 4.0 in general helps if there is a lack of memory, but cannot replace a larger memory with a significantly higher bandwidth.

The Radeon RX 5600 XT also gets faster with PCIe 4.0 in the adapted test course if you run out of memory. At 9 percent, however, the advantage is not quite as great as with the smaller model. Nevertheless, it shows that even with 16 PCIe-Lanes PCIe 4.0 gives an advantage in the case of lack of memory – 32 instead of 16 GB / s via the PCIe slot help here. In the benchmarks of the Radeon RX 5700, however, there is a tie between PCIe 3.0 and PCIe 4.0, but the built-in 8 GB memory is always sufficient.

The performance rating with the reduced texture details then clearly shows what could be assumed from the previous results: Without VRAM deficiency, PCIe 4.0 does not bring any relevant advantages over PCIe 3.0 even with the only eight lanes on the Radeon RX 5500 XT. For all four graphics cards tested, PCIe 4.0 only works 1 percent faster than PCIe 3.0.

Not only for the frame times, but also for the frame rate, PCIe 4.0 can bring an advantage in the event of a lack of memory. However, this is less than with the frame times, because here the Radeon RX 5500 XT no longer benefits by 19, but "only" by 12 percent. The Radeon RX 5600 XT increased by 6 instead of 11 percent. With low texture details, the plus is again consistently 1 percent.

Ghost Recon Breakpoint is a memory eater and the extreme case in the test course. There are massive differences, especially in frame times. Especially the Radeon RX 5500 XT with 4 GB has great difficulties in the game. PCIe 4.0 brings a plus of 16 percent, but that's almost nothing if you consider that the 8 GB version will be almost 50 percent faster again. In Breakpoint there are no differences between the PCIe versions.

The Radeon RX 5600 XT, on the other hand, increases massively with PCIe 4.0 and is just 48 percent faster and almost approaches the frame times of the Radeon RX 5700. The discrepancy with the Radeon RX 5500 XT with 4 GB is striking. Presumably, due to the 2 GB smaller memory and at the same time only half the bandwidth to the slot (because of the 8 instead of 16 lanes), it gets so much into trouble that it is no longer enough to double the low bandwidth.

If you look at the low texture details of the game, you will also find that the Radeon RX 5600 XT has better frame times than the Radeon RX 5700, since the game obviously can't do anything with the larger model's memory bandwidth. With the high-resolution textures, however, the frame times are 6 percent worse. As with the Radeon RX 5500 XT, this shows that PCIe 4.0 is helpful when there is a lack of memory, but cannot replace a larger memory.

F1 2019 is the exact opposite of Breakpoint. Only the Radeon RX 5500 XT with 4 GB still shows an advantage of 10 percent with PCIe 4.0, all other graphics cards can no longer benefit.

Conclusion

This test also shows that a Radeon RX 5700 and a Radeon RX 5700 XT do not currently benefit from PCIe 4.0 in games because their 8 GB of memory are always sufficient. The PCIe slot is therefore not required for time-critical reloading of textures. The now released Radeon RX 5500 XT and Radeon RX 5600 XT have disadvantages compared to the larger model in terms of memory expansion and / or the number of PCIe lanes. And it becomes clear that PCIe 4.0 brings tangible advantages in such a case.

However, PCIe 4.0 is not a general problem-solver either, because on both the Radeon RX 5500 XT and the Radeon RX 5600 XT, double the transfer rate via the PCIe bus only brings an advantage if there is a lack of memory – this is also the reason why the Radeon RX 5700 with their 8 GB doesn't benefit. On the Radeon RX 5500 XT, PCIe 4.0 can only hide the problems and not replace the larger memory – in this case there is no way around 8 GB. Since the Radeon RX 5600 XT with 6 GB relies on a slightly larger memory, the greatest practical advantages are shown here, since PCIe 4.0 on the graphics card can at least largely, if not completely, compensate for the lack of memory.

If you have a Radeon RX 5700 (XT), you do not need to think about upgrading to PCIe 4.0, since PCIe 4.0 does not currently offer any advantages in games apart from lack of memory. And even with a Radeon RX 5500 XT it is not necessary because the advantages are not big enough; the 8 GB version should be used there straight away. Only the Radeon RX 5600 XT benefits noticeably from the four Navi models and also sensibly from PCIe 4.0, because the interface can virtually compensate for the 2 GB disadvantage.

The problem: A Ryzen 3000 CPU and a rather expensive X570 motherboard are absolutely necessary and that bites with the fact that a Radeon RX 5600 XT is actually intended for use in an inexpensive PC.

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