[Hardware] AMD Unveils Big Navi: RX 6900 XT, RX 6800 XT and RX 6800 Take On Ampere

[_Happy boy]

 

The Radeon RX 6000 series is much more than a value alternative; AMD plans to go against Nvidia's best and may come out ahead.

 

AMD just dropped the Big Navi bombshell, which you can view above, detailing key specs for the Radeon RX 6800 XT, Radeon RX 6800… oh, and one more thing: Radeon RX 6900 XT. AMD is gunning for the top of the GPU benchmarks hierarchy and best graphics card lists in a big way.

The graphics card names aren't surprising, and most of the specs were at least guesstimated as far back as six months ago — our AMD Big Navi hub has been filled with speculation for some time, and we weren't too far off, mostly. But this time, we've got AMD's official full specs, pricing, and even some comparative benchmarks at 4K and 1440p. It looks as though AMD isn't just hoping to come close to Nvidia's Ampere GPUs, it has a very good chance of taking the lead in both GPU performance and efficiency for the first time in over a decade. Could this be AMD's ‘Ryzen moment’ for the GPU sector? Let's cover what AMD revealed and what it means for our next graphics card purchase. 

AMD RX 6000 Key Points

Up to 5120 shader cores in RX 6900 XT, 3840 cores in RX 6800
Maximum boost clocks of 2.1-2.25 GHz
16GB of GDDR6 for the three cards revealed today
128MB Infinity Cache more than doubles effective bandwidth
One Ray Accelerator per CU, 10x speedup for RT calculations
Prices of $999, $649 and $579 for 6900 XT, 6800 XT and 6800
Upcoming FidelityFX enhancements to offer DLSS alternative

 

We'll dig into all the details below, but early indications are that Big Navi is going to live up to its name. It doesn't have the raw core counts of Nvidia's Ampere architecture, but theoretical TFLOPS don't always match real-world performance. In fact, AMD has previously held an advantage in TFLOPS relative to Nvidia but still ended up trailing in gaming performance. The Infinity Cache and other changes may flip the tables this time, as a large cache can help eliminate many trips to VRAM for framebuffer accesses. 

AMD Radeon RX 6800 XT Specs and Performance Preview 
Let's start with the primary contender, the Radeon RX 6800 XT. This will go up against Nvidia's GeForce RTX 3080, which is theoretically priced starting at $700, but in practice, you can't buy the RTX 3080 right now. Well, maybe you can if you get lucky, but supply definitely isn't meeting the current demand, and it may not do so until 2021. AMD might be able to help with that, however, as the RX 6800 XT boasts some impressive-looking specs and initial performance figures (take with a grain of salt, as with any manufacturer-provided benchmarks) — oh, and the 6800 XT will have a starting price of $649. Here's a look at the main specs: 

The most recent rumors were basically correct, and it makes sense. RX 6800 XT will have 72 CUs (Compute Units), each with 64 shader cores. The game clock sits at just over 2GHz, while the boost clock (which if it's anything like Navi 1x is basically a maximum that you'll rarely see) is 2.25GHz. Combined, that works out to peak compute performance of 20.7 TFLOPS. That's technically a lot less than RTX 3080's 29.8 TFLOPS, but a chunk of the Nvidia potential performance ends up going to INT32 calculations.

What's not clear right now is whether AMD has added concurrent FP32 + INT32 data paths to RDNA2 / Navi 2x, or if there are other optimizations that make up for the apparent compute deficit. If it has, real-world performance will probably end up being quite close to the RTX 3080, maybe even surpassing it. Even if it doesn't have concurrent INT+FP, though… Well, let's get to perhaps the most interesting aspect of the new architecture, the 128MB Infinity Cache.Put simply, that's a huge cache. AMD didn't go into all the details, but the basic idea is to reduce the amount of memory traffic and thereby increase effective bandwidth by having an L3 (L4?) cache that's large enough to hold the entire frame buffer — and maybe a bit more. Reducing all of that extra memory traffic can also significantly improve overall efficiency, which is exactly what AMD says RDNA2 does. With the same 256-bit GDDR6 interface, apparently still running at a 'mere' 14 Gbps, AMD says the new Infinity Cache cuts power use by 10 percent while increasing the effective bandwidth by 117 percent. If true, that means RX 6800 XT has the equivalent of about 972 GBps of bandwidth, significantly more than the RTX 3080.

It's important to point out the other two pieces of data: The 16GB total GDDR6 memory and the 300W TBP (Total Board Power). That's 60 percent more memory for textures and other data compared to the RTX 3080. We've questioned whether 10GB was enough for Nvidia's RTX 3080, and the answer is that it probably is. Still, having more memory won't hurt performance — it can only help. As for the 300W TBP, AMD and Nvidia don't always measure power in the same way, but AMD says the 300W should be the total amount of power the cards will consume, meaning it will actually be 20W less than the RTX 3080. Except, in our own power testing, the RTX 3080 tended to land closer to 330W.

Anyway, let's hit the preliminary benchmarks. Usual caveats applied, grains of salt, etc. How does AMD say the RX 6800 XT performs? Take a look at these 4K and 1440p ultra RX 6800 XT vs. RTX 3080 benchmarks:

Based on AMD's numbers, RX 6800 XT isn't just competitive with the RTX 3080; it will be slightly faster. Of course, AMD is probably selecting games that favor its GPU a bit, and it's worth noting that none of these benchmarks enabled ray tracing. Still, if AMD can match RTX 3080 performance on average, with more memory, less power, and a lower price? That looks like a win to us, pending independent testing, of course.

AMD Radeon RX 6800 Specs and Performance Preview 
The RX 6800 XT is the RTX 3080 competitor, at a slightly lower price point, but AMD isn't stopping there. Big Navi, or Navi 21, is the GPU at the heart of the 6800 XT, and it will also feature in a slightly more cut down variant that drops the XT. The Radeon RX 6800 is to Navi 21 what the RX 5700 was to Navi 10: fewer cores, lower clocks, but still a lot of performance. Oh, and it will cost less — $70 less, to be precise. The starting price for the RX 6800 is $579.

Most of the core features are similar, only instead of 72 CUs and 4608 shader cores, the RX 6800 will have 60 CUs and 3840 shader cores. It also has advertised clock speeds that are about 150-200 MHz lower, leading to theoretical compute performance of 16.2 TFLOPS. However, it still packs the full 128MB Infinity Cache and 16GB of GDDR6, and the reduced clocks and core counts give it a 250W TBP. In short, RX 6800 is going after the GeForce RTX 3070. It's going to be an interesting matchup.

Considering how the RTX 3070 stacks up against the RTX 3080 (it's about 25 percent slower at 4K), AMD looks to be in a very good position for the more modest high-end GPU market. The 6800 XT has about 30 percent less compute than the RTX 3080, but the RX 6800 only has about 20 percent less compute than the RTX 3070. It also has twice as much memory and potentially way more effective memory bandwidth thanks to the Infinity Cache.

Again, caveats and disclaimers apply, and AMD didn't have the RTX 3070 for testing. But it did have the RTX 2080 Ti, which in our own testing is a few percent faster than the RTX 3070. Here are AMD's results: