AMD Big Navi, Navi 2x, RDNA 2. Whatever you want to call them, AMD's next-generation GPUs are promising big performance and efficiency gains, along with feature parity with Nvidia in terms of ray tracing support. Will Team Red finally take the pole position in our GPU hierarchy and lay claim to the crown for the best graphics card, or will Nvidia's upcoming Ampere architecture spoil the party? It's too soon to say, but here's everything we know about Big Navi, including the RDNA 2 architecture, potential performance, expected release date and pricing.
We've done our best to sort fact from fiction, but even without hard numbers from AMD, we have a good idea of what to expect. The recent Xbox Series X and PlayStation 5 hardware announcements certainly add fuel to the fire, and give us realistic ideas of where Big Navi is likely to land in the PC world. Let's start at the top, with the new RDNA 2 architecture that powers Big Navi / Navi 2x. But first, heres a brief list of what we know (or think we know) so far.
Big Navi / RDNA 2 at a Glance
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The RDNA 2 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. RDNA 2 looks to double 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 dispatched. 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 adds 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 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% performance advantage, but it uses 300W compared to the RX 5700 XT's 225W. In short, AMD is 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 RDNA 2 appears to carry over all of that, with one major new addition: Support for ray tracing. It also supports Variable Rate Shading (VRS), which is part of the DirectX 12 Ultimate spec. There will almost certainly be other tweaks to the architecture, as AMD is making some big claims about Big Navi / RDNA 2 / Navi 2x when it comes to performance per watt. Specifically, AMD says RDNA 2 will 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. It means AMD claims RDNA 2 will deliver either the same performance while using 33% less power, or 50% higher performance with the same power, or most likely some in between solution with higher performance and lower power requirements.
The one thing we know for certain is that RDNA 2 / Big Navi / Navi 2x GPUs will all support hardware ray tracing. That will bring AMD up to feature parity with Nvidia. Note that Nvidia also has Tensor cores in its Turing architecture, which are used for deep learning and AI computations, as well as DLSS (Deep Learning Super Sampling), which has now been generalized with DLSS 2.0 to improve performance and image quality and make it easier for games to implement DLSS. So far, AMD has said nothing about RDNA 2 / Navi 2x including Tensor cores or an equivalent to DLSS, though AMD's CAS (Contrast Aware Sharpening) and RIS (Radeon Image Sharpening) do overlap with DLSS in some ways.
Regarding ray tracing, there was some question as to whether AMD would use the same BVH approach to ray tracing calculations as Nvidia, and with the PlayStation 5 and Xbox Series X announcements out of the way, the answer appears to be yes. 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. While AMD didn't provide much detail on its BVH hardware, BVH as a core aspect of ray tracing was definitely mentioned, and we heard similar talk about ray tracing and BVH with the VulkanRT and DirectX 12 Ultimate announcements.
We don't know how much ray tracing hardware is present, or how fast will it be. If AMD takes the same approach as Nvidia and puts one RT core (or whatever AMD wants to call it) into each CU, the comparison between AMD and Nvidia might be easier. However, AMD could mix things up. Instead of one RT unit per CU, maybe it puts two RT cores into each WGP, or four RT cores per WGP, or some other breakdown of computing elements. The fact is, we don't know yet and won't know until AMD says more.
We also know that AMD is planning multiple Navi 2x products, and we expect to see extreme, high-end and mainstream options though budget Navi 2x seems unlikely, given RX 5500 XT launched this year. AMD could launch multiple GPUs in a relatively short period of time, but more likely we'll see the highest performance options first, followed by high-end and eventually mid-range solutions. Some of those may not happen until 2021, however.
Console Specifications and a Historical Recap
We don't know how many CUs will be present in Navi 2x, for any of the configurations, but there are hints as to what we can expect thanks to the console announcements. We're going to provide a lot of background information on the previous-generation consoles, as well as the upcoming consoles, to help inform our specification speculation. You've been warned.
Xbox Series X will have a relatively-massive 52 CUs in its GPU, while the PlayStation 5 will 'only' have 36 CUs. Sony's PS5 CUs are clocked higher in the PS5, but in terms of raw performance the Xbox Series X is clearly faster. Looking at historical console hardware launches, it's safe to bet that neither represents the pinnacle of what AMD will launch in PC hardware this year.
Back in 2013, when the PlayStation 4 and Xbox One first launched, the PS4 clearly had the faster GPU. It had 18 CUs or 1152 GPU cores running at 800 MHz, compared to the Xbox One with 12 CUs or 768 cores running at 853 MHz. That's 1843 GFLOPS for the PS4 vs. 1310 GFLOPS on the Xbox One. More importantly, though, is the PC graphics hardware AMD was shipping at the time.
The Radeon HD 7970 GHz Edition had been shipping for over a year with 32 CUs and 2048 GPU cores, and up to 4301 GFLOPS. The R9 290X launched around the same time as the PS4 and Xbox One, with 44 CUs and 2816 cores, and the 1050 MHz clock speed meant 5632 GFLOPS. That means AMD's top PC GPU when the PS4 launched was about three times as fast, though the PS4 was closer in terms of memory bandwidth (256 GBps on PS4 vs. 320 GBps on the 290X).
The same thing happened in 2017 with the console updates. PS4 Pro moved to 36 CUs and 2304 cores, with a 911 MHz core clock providing up to 4198 GFLOPS of compute. The Xbox One X had 40 CUs and 2560 cores clocked at 1172 MHz for 6001 GFLOPS. The Xbox is basically using a consolized variant of the RX 580, while the PS4 Pro is using a consolized RX 570. The top PC GPU from AMD in 2017 was RX Vega 64, with 64 CUs and 4096 cores running at up to 1677 MHz, yielding 13,738 GFLOPS of compute. Again, PC hardware was at least twice the compute performance and since we're comparing similar architectures, it's a 'fair' comparison (ie, unlike comparing GFLOPS between AMD and Nvidia GPUs).