AMD Big Navi, RX 6000, Navi 2x, RDNA 2. Whatever the name, AMD’s latest GPUs promise big performance and efficiency gains, along with feature parity with Nvidia in terms of ray tracing support. Team Red finally puts up some serious competition in our GPU benchmarks hierarchy and provides several of the best graphics cards, going head to head with the Nvidia Ampere architecture.
AMD officially unveiled Big Navi on October 28, 2020, including specs for the RX 6900 XT, RTX 6800 XT, and RTX 6800. The Radeon RX 6800 XT and RX 6800 launched first, followed by the Radeon RX 6900 XT. In March 2021, AMD released the Radeon RX 6700 XT, and more recently the Radeon RX 6600 XT. So far, we haven’t seen a trimmed down Navi 22 variant (except in mobile), and AMD instead opted to create Navi 23, the smallest ‘Big Navi’ GPU to date at less than half the size of Navi 21. We’ve updated this article with revised details, though there are still future RDNA2 products yet to be revealed.
Based on what we’ve seen, Big Navi has finally put AMD’s high graphics card power consumption behind it. Or at least, Big Navi is no worse than Nvidia’s RTX 30-series cards, considering the 3080 and 3090 have the highest Nvidia TDPs for single GPUs ever. Let’s start at the top, with the new RDNA2 architecture that powers RX 6000 / Big Navi / Navi 2x. Here’s everything we know about AMD Big Navi, including the RDNA 2 architecture, specifications, performance, pricing, and availability.
Big Navi / RDNA2 at a Glance
- Up to 80 CUs / 5120 shaders
- 50% better performance per watt
- Launched November 18 (RX 6800 series) and December 8 (RX 6900 XT)
- Pricing of $379 to $999 for RX 6600 XT to RX 6900 XT
- Full DirectX 12 Ultimate support
The RDNA2 Architecture in Big Navi
Every generation of GPUs is built from a core architecture, and each architecture offers improvements over the previous generation. It’s an iterative and additive process that never really ends. AMD’s GCN architecture went from first generation for its HD 7000 cards in 2012 up through fifth gen in the Vega and Radeon VII cards in 2017-2019. The RDNA architecture that powers the RX 5000 series of AMD GPUs arrived in mid 2019, bringing major improvements to efficiency and overall performance. RDNA2 doubled down on those improvements in late 2020.
First, a quick recap of RDNA 1 is in order. The biggest changes with RDNA 1 over GCN involve a redistribution of resources and a change in how instructions are handled. In some ways, RDNA doesn’t appear to be all that different from GCN. The instruction set is the same, but how those instructions are dispatched and executed has been improved. RDNA also added working support for primitive shaders, something present in the Vega GCN architecture that never got turned on due to complications.
Perhaps the most noteworthy update is that the wavefronts—the core unit of work that gets executed—have been changed from being 64 threads wide with four SIMD16 execution units, to being 32 threads wide with a single SIMD32 execution unit. SIMD stands for Single Instruction, Multiple Data; it’s a vector processing element that optimizes workloads where the same instruction needs to be run on large chunks of data, which is common in graphics workloads.
This matching of the wavefront size to the SIMD size helps improve efficiency. GCN issued one instruction per wave every four cycles; RDNA issues an instruction every cycle. GCN used a wavefront of 64 threads (work items); RDNA supports 32- and 64-thread wavefronts. GCN has a Compute Unit (CU) with 64 GPU cores, 4 TMUs (Texture Mapping Units) and memory access logic. RDNA implements a new Workgroup Processor (WGP) that consists of two CUs, with each CU still providing the same 64 GPU cores and 4 TMUs plus memory access logic.
How much do these changes matter when it comes to actual performance and efficiency? It’s perhaps best illustrated by looking at the Radeon VII, AMD’s last GCN GPU, and comparing it with the RX 5700 XT. Radeon VII has 60 CUs, 3840 GPU cores, 16GB of HBM2 memory with 1 TBps of bandwidth, a GPU clock speed of up to 1750 MHz, and a theoretical peak performance rating of 13.8 TFLOPS. The RX 5700 XT has 40 CUs, 2560 GPU cores, 8GB of GDDR6 memory with 448 GBps of bandwidth, and clocks at up to 1905 MHz with peak performance of 9.75 TFLOPS.
On paper, Radeon VII looks like it should come out with an easy victory. In practice, across a dozen games that we’ve tested, the RX 5700 XT is slightly faster at 1080p gaming and slightly slower at 1440p. Only at 4K is the Radeon VII able to manage a 7% lead, helped no doubt by its memory bandwidth. Overall, the Radeon VII only has a 1-2% performance advantage, but it uses 300W compared to the RX 5700 XT’s 225W.
In short, AMD was able to deliver roughly the same performance as the previous generation, with a third fewer cores, less than half the memory bandwidth and using 25% less power. That’s a very impressive showing, and while TSMC’s 7nm FinFET manufacturing process certainly warrants some of the credit (especially in regards to power), the performance uplift is mostly thanks to the RDNA architecture.
That’s a lot of RDNA discussion, but it’s important because RDNA2 carries all of that forward, with several major new additions. First is support for ray tracing, Variable Rate Shading (VRS), and everything else that’s part of the DirectX 12 Ultimate spec. The other big addition is, literally, big: a 128MB Infinity Cache that help optimize memory bandwidth and latency. (Navi 22 has a 96MB Infinity Cache and Navi 23 gets by with a 32MB Infinity Cache.)
There are other tweaks to the architecture, but AMD made some big claims about Big Navi / RDNA2 / Navi 2x when it comes to performance per watt. Specifically, AMD said RDNA2 would offer 50% more performance per watt than RDNA 1, which is frankly a huge jump—the same large jump RDNA 1 saw relative to GCN. Even more importantly, AMD mostly succeeded. The RX 6600 XT ended up delivering slightly higher overall performance than the RX 5700 XT, while using 30% less power. Alternatively, the RX 6700 XT has the same 40 CUs as the RX 5700 XT, and it’s about 30% faster than the older card while using a similar amount of power.
The other major change with RDNA2 involves tuning the entire GPU pipeline to hit substantially higher clockspeeds. Previous generation AMD GPUs tended to run at substantially lower clocks than their Nvidia counterparts, and while RDNA started to close the gap, RDNA2 flips the tables and blows past Nvidia with the fastest clocks we’ve ever seen on a GPU. Game Clocks across the entire RX 6000 range are above 2.1GHz, and cards like the RX 6700 XT and RX 6600 XT can average speeds of around 2.5GHz while gaming. Clock speeds aren’t everything, but all else being equal, higher clocks are better, and the >20% boost in typical clocks accounts for a large chunk of the performance improvements we see with RDNA2 vs. RDNA GPUs.
RDNA2 / Big Navi / RX 6000 GPUs support ray tracing, via DirectX 12 Ultimate or VulkanRT. That brings AMD up to feature parity with Nvidia. AMD uses the same BVH approach to ray tracing calculations as Nvidia (it sort of has to since it’s part of the API). If you’re not familiar with the term BVH, it stands for Bounding Volume Hierarchy and is used to efficiently find ray and triangle intersections; you can read more about it in our discussion of Nvidia’s Turing architecture and its ray tracing algorithm.
AMD’s RDNA2 chips contain one Ray Accelerator per CU, which is similar to what Nvidia has done with it’s RT cores. Even though AMD sort of takes the same approach as Nvidia, the comparison between AMD and Nvidia isn’t clear cut. The BVH algorithm depends on both ray/box intersection calculations and ray/triangle intersection calculations. AMD’s RDNA2 architecture can do four ray/box intersections per CU per clock, or one ray/triangle intersection per CU per clock.
From our understanding, Nvidia’s Ampere architecture can do up to two ray/triangle intersections per RT core per clock, plus some additional extras, but it’s not clear what the ray/box rate is. In testing, Big Navi RT performance generally doesn’t come anywhere close to matching Ampere, though it can usually keep up with Turing RT performance. That’s likely due to Ampere’s RT cores doing more ray/box and ray/triangle intersections per clock.
The Infinity Cache is perhaps the most interesting change. By including a whopping 128MB cache (L3, but with AMD branding), AMD should be able to keep basically all of the framebuffer cached, along with the z-buffer and the some recent textures. That will dramatically reduce memory bandwidth use and latency, and AMD claims the Infinity Cache allows the relatively tame GDDR6 16 Gbps memory to deliver an effective bandwidth that’s 2.17 times higher than the raw numbers would suggest.
The Infinity Cache also helps with ray tracing calculations. We’ve seen on Nvidia’s GPUs that memory bandwidth can impact RT performance on the lower tier cards like the RTX 2060, but it might also be memory latency that’s to blame. We can’t test AMD Big Navi performance in RT without the Infinity Cache, however, and all we know is that RT performance tends to lag behind Nvidia.
The Infinity Cache propagates down to the lower tier RDNA2 chips, but in different capacities. 128MB is very large, and based on AMD’s image of the die, it’s about 17 percent of the total die area on Navi 21. The CUs by comparison are only about 31 percent of the die area, with memory controllers, texture units, video controllers, video encoder/decoder hardware, and other elements taking up the rest of the chip. Navi 22 and Navi 23 have far lower CU counts, and less Infinity cache as well. Navi 22 has a 96MB L3 cache, while Navi 23 trims that all the way down to just 32MB. Interestingly, even with only one fourth the Infinity Cache, the RX 6600 XT still managed to outperform the RX 5700 XT at 1080p and 1440p — despite having 43% less raw bandwidth.
One big difference between AMD and Nvidia is that Nvidia also has Tensor cores in its Ampere and Turing architectures, which are used for deep learning and AI computations, as well as DLSS (Deep Learning Super Sampling). AMD doesn’t have a Tensor core equivalent, though its FidelityFX Super Resolution does offer somewhat analogous features and works on just about any GPU. Meanwhile, Intel’s future Arc Alchemist architecture will also have tensor processing elements, and XeSS will have a fall-back mode that runs using DP4a code on other GPUs.
AMD already has multiple Navi 2x products, though more variants may still be forthcoming. The RDNA2 architecture is also being used in some upcoming smartphone chips like the Samsung Exynos 2100, likely without any Infinity Cache and with far different capabilities in terms of performance. At present, AMD’s RX 6000 cards span the midrange to extreme performance categories, but even the lowest tier RX 6600 XT still carries a high-end price.
RX 6000 / Big Navi / Navi 2x Specifications
That takes care of all the core architectural changes. Now let’s put it all together and look at the currently announced RDNA2 / RX 6000 / Big Navi GPUs. AMD basically doubled down on Navi 10 when it comes to CUs and shaders, shoving twice the number of both into the largest Navi 21 GPU. At the same time, Navi 10 is relatively small at just 251mm square, and Big Navi is more than double that in its largest configuration. We’ll include the RX 5700 XT and Navi 10 in the following specs table as a point of reference.
|Graphics Card||RX 6900 XT||RX 6800 XT||RX 6800||RX 6700 XT||RX 6600 XT||RX 5700 XT|
|Architecture||Navi 21||Navi 21||Navi 21||Navi 22||Navi 23||Navi 10|
|Process Technology||TSMC N7||TSMC N7||TSMC N7||TSMC N7||TSMC N7||TSMC N7|
|Die size (mm^2)||519||519||519||336||237||251|
|Base Clock (MHz)||1825||1825||1700||2321||1968||1605|
|Boost Clock (MHz)||2250||2250||2105||2581||2589||1755|
|VRAM Speed (Gbps)||16||16||16||16||16||14|
|VRAM Bus Width||256||256||256||192||128||256|
|TFLOPS FP32 (Boost)||23||20.7||16.2||13.2||10.6||9|
|Launch Date||Dec 2020||Nov 2020||Nov 2020||Mar 2021||Aug 2021||Jul 2019|
The highest spec parts all use the same Navi 21 GPU, just with differing numbers of enabled functional units. Navi 21 has 80 CUs and 5120 GPU cores, and is more than double the size (519mm square) of the previous generation Navi 10 used in the RX 5700 XT. But a big chip means lower yields, so AMD has parts with 72 and 60 CUs as well.
The Radeon RX 6900 XT seems to be shipping in more limited quantities, but then all of the RDNA2 GPUs with the possible exceptions of the RX 6700 XT and RX 6600 XT have been hard to come by. Look at our GPU price index and you can see how many of each card has been sold (resold) on eBay during the past several months. The short summary is that Nvidia RTX 30-series GPUs are selling in far higher quantities.
What’s interesting is how the die sizes and other features line up. Big Navi / RDNA2 adds support for ray tracing and other DX12 Ultimate features, which requires quite a few transistors. The very large Infinity Cache is also going to use up a huge chunk of die area, but it also helps overcome potential bandwidth limitations caused by the somewhat narrow 256-bit bus width on Navi 21. Ultimately, Navi 23 ends up with a slightly smaller die than Navi 10, but with similar performance and the additional new features.
Besides the already released cards, it’s interesting to note the gaps that still exist. RX 6700 XT remains the only card that uses Navi 22 (other than some mobile variants), and RX 6600 XT is the only card using Navi 23 so far. We will likely see additional card models in the future, like a non-XT RX 6600 and maybe even RX 6700, but AMD will probably wait until its supply of GPUs and other components improves before trying to launch more cards.
One thing that has truly impressed with RDNA2 is the Infinity Cache. Not only does AMD give lots of VRAM for the various models (well, except maybe the RX 6600 XT, which feels a bit thin at 8GB for a $380 card), but the Infinity Cache truly does help with real-world performance. The RX 6700 XT as an example has less bandwidth than the RTX 3060 Ti and yet still keeps up with it in gaming performance, and the same goes for the RX 6800 XT vs. the RTX 3080.
At some point, we may also see an RX 6500 XT, though it may not be worth pursuing a lower tier GPU at this point. It would be interesting to see something like a 6GB card with a 96-bit interface and a 32MB Infinity Cache, but unless AMD can produce and sell such a card for under $200, we’re not particularly interested.
As far as a true budget Navi 2x card is concerned, no one is posting any real information on that yet. There might be a Navi 24 or something in the coming year, with only 20–24 CUs max. That would put it at the level of the Xbox Series S, at which point we’re not sure if it’s really worth including ray tracing support. We’ll have to see how things develop in the coming months, though, as 1080p with FSR might run fine on such a GPU.
Big Navi / Navi 2x Performance
With the official launches now complete, we have created the above charts using our own suite of 13 games run at three resolutions. All of the testing was done on a Core i9-9900K setup, with resizable BAR support enabled on the BIOS. The performance of RDNA2 and RX 6000 cards are good to great in rasterization games, but AMD generally comes up short of the competition in ray tracing workloads.
At the top, the RX 6900 XT goes up against the RTX 3090 and RTX 3080 Ti. AMD leads at 1080p, where the Infinity Cache benefits it the most, while the 3090 leads at 1440p and the 3080 Ti also comes out ahead of AMD’s best at 4K. The RX 6800 XT meanwhile takes down the RTX 3080, and the RX 6800 beats the RTX 3070 Ti. Further down the charts, the RX 6700 lands between the RTX 3060 Ti and RTX 3070, and the RX 6600 XT generally beats the RTX 3060 (except at 4K).
Of course, that’s only in traditional rasterization games. We’ve used a different suite of games with ray tracing enabled, and we’ve run benchmarks for each of the major GPU launches of the past year. The 10 games are the same as from the RX 6600 XT launch review (Bright Memory Infinite, Control, Cyberpunk 2077, Dirt 5, Fortnite, Godfall, Metro Exodus, Minecraft, Shadow of the Tomb Raider, and Watch Dogs Legion). Here’s the overall summary charts for 1440p and 1080p, running natively (without DLSS).
That… doesn’t look good for AMD. Granted, there are a couple of games (Godfall and Dirt 5) where AMD performance is far closer to what we saw in the earlier rasterization performance charts. However, those games only use one RT effect, ray traced shadows, and frankly the difference in image quality is pretty minor at best — just like in Shadow of the Tomb Raider. Also, those are two AMD promotional games, and Godfall at least has some questionable design decisions (it really runs poorly with less than 12GB VRAM, for example).
As more RT effects get used, Nvidia’s Ampere GPUs tend to widen their performance advantage. In our RT test suite, the RX 6900 XT is the fastest RDNA2 card and it ends up just slightly ahead of the RTX 3070 Ti, with the RX 6800 XT falling a hair behind the RTX 3070 Ti. The RX 6800 now lands between the RTX 3070 and RTX 3060 Ti, and the RX 6700 XT trails the RTX 3060 Ti and comes in about 10% ahead of the RTX 3060. Meanwhile, the RX 6600 XT clearly has problems, either from a lack of VRAM, the smaller Infinity Cache size, or maybe drivers — or likely from all of the above. We’ll have to revisit that in the future, like maybe once Windows 11 gets released.
Big Navi and RX 6000 Closing Thoughts
AMD provided a deeper dive into the RDNA2 architecture at Hot Chips 2021. We’ve used several of the slides in our latest updates, but the full suite is in the above gallery for reference.
AMD has a lot riding on Big Navi, RDNA2, and the Radeon RX 6000 series. After playing second fiddle to Nvidia for the past several generations, AMD is taking its shot at the top. AMD has to worry about more than just PC graphics cards, though. RDNA2 is the GPU architecture that powers the next generation of consoles, which tend to have much longer shelf lives than PC graphics cards. Look at the PS4 and Xbox One: both launched in late 2013 and are still in use today.
If you were hoping for a clear win from AMD, across all games and rendering APIs, that didn’t happen. Big Navi performs great in many cases, but with ray tracing it looks decidedly mediocre. Higher performance in games that don’t use ray tracing might be more important today, but a year or two down to road, that could change. Then again, the consoles have AMD GPUs and are more likely to see AMD-specific optimizations, so AMD isn’t out of the running yet.
Just as important as performance and price, though, we need actual cards for sale. There’s clearly demand for new levels of performance, and every Ampere GPU and Big Navi GPU so far has sold out as quickly as the products are available for purchase. There’s only so much silicon to go around, sadly. Samsung apparently can’t keep up with demand for Ampere GPUs, and TSMC has a lot more going on — it can only produce so many N7 wafers per month! Based on what we’ve seen in our GPU price index and the latest Steam Hardware Survey, Nvidia has sold probably ten times as many Ampere GPUs as AMD has sold RDNA2 cards.
The bottom line is that if you’re looking for a new high-end graphics card, Big Navi is a good competitor. But if you want something that can run every game at maxed out settings, even with ray tracing, at 4K and 60 fps? Not even the RTX 3090 can manage that, which means even while we’re plagued with shortages on all the current GPUs, we’re already looking toward the future next-gen GPUs.
Save us, Lovelace and RDNA3. You’re our only hope! And thankfully, Ethereum mining will no longer be a thing come next year (though a different coin might take its place).