AMD Radeon RX 7900 XTX and XT Review: Shooting for the Top

We've tested the AMD Radeon RX 7900 XTX and Radeon RX 7900 XT, and we have the full results ready for your enjoyment — one day before the official launch party. AMD's latest and greatest RDNA 3 architecture and the RX 7900-Series graphics cards are all set to party with Nvidia's Ada Lovelace architecture and the GeForce RTX 4080 as they vie for a spot on our list of the best graphics cards.

One thing AMD won't do: Take down the GeForce RTX 4090 that sits at the top of our GPU benchmarks hierarchy. AMD has said that it doesn't feel the need to compete directly against a $1,600 (or more!) graphics card, but several senior people at AMD also indicate that Nvidia's AD102 chip was "bigger than expected" and basically out of reach.

What may also be out of reach for many of our readers are the new AMD RX 7900-series cards. While they cost less than Nvidia's RTX 4090 and 4080, with prices starting at $899 for the slower — and frankly less desirable — RX 7900 XT, these are clearly not going after the mainstream gamer market. That task will likely fall to the future Navi 32 / RX 7700-series cards (or maybe 7800-series). For now, if you want AMD's fastest ever consumer graphics card, be prepared to fork over a wad of cash.

We've already done an in-depth look at the RDNA 3 architecture and a preview of the cards, so start with those articles if you want to get up to speed. With actual hardware in hand and a bevy of benchmarks under our belts, that's the main event today. But we do have some additional thoughts, and we'll start as always with the specifications of AMD's latest cards, with Nvidia and some previous generation GPUs for comparison.
 

There's a lot to unpack in the specs, but we'll mostly focus on AMD's new chips. The RX 7900 XTX has the fully enabled Navi 31 GCD (Graphics Compute Die) along with six MCDs (Memory Cache Dies), while the 7900 XT disables a dozen compute units (CUs) in the GCD and one of the MCDs is fused off. Technically there are still six MCD chips present, to ensure even mounting pressure from the heatsink, but one of them is fused off (it could be a non-functional MCD).

The GPU shader counts are where things start to get a bit different from other architectures. AMD says there are still 64 Streaming Processors (SP) per CU, but there are now four SIMD32 vector units per CU as well — two of which can only process FP32 or Matrix operations and not INT32. We're going to call each of these a GPU shader, which goes along with AMD's peak throughput data of 61.4 teraflops FP32 on the 7900 XTX. This is similar to what Nvidia did with Ampere (and now Ada), so just know that the official SP count is no longer the same as the potential GPU shaders count.

We've also received some clarification on the "AI Accelerators" that are part of the RDNA 3 architecture. The short summary is that they repurpose the SIMD32 units to do matrix operations instead of FP32 (or FP16). They also support BF16 (16-bit brain-float) formats and INT8 alongside FP16. All three of those (FP16/BF16/INT8) have the same peak throughput that's double the FP32 single-precision floating-point throughput.

What's the difference between the previous half-precision FP16 shader support and the AI Accelerator FP16 support? Basically, it comes down to optimizing throughput and reducing power consumption, with some new instructions that are supported in matrix mode. Obviously, the peak FP16/BF16 rates are significantly lower than what the RTX 4080 and 4090 can deliver. Finding software that specifically uses the AI Accelerator on AMD's RDNA 2 / RDNA 3 GPUs is also proving difficult right now, so we may need to revisit the subject at a later date.

Of course, one of the big deals with RDNA 3 and Navi 31 is the move to a chiplet architecture. Separating the memory and cache from the rest of the GPU functionality helps to bring prices down, or at least it reduces AMD's costs. It could also open the door to higher performance future designs. For now, however, it's important to note that all indications are that the use of chiplets does represent something of a performance compromise.

Not to jump ahead here, but if you look at the paper specs and see 160% more theoretical compute and 67% more memory bandwidth compared to the RX 6950 XT, clearly that doesn't really match up with AMD's own benchmarks that suggest more like a 50–80 percent improvement in individual games (around 60% on average). We feel some of that comes from additional overhead and latency associated with the use of chiplets. In other words, RDNA 3 chiplets feel a bit more like Zen 2 chiplets rather than, say, Zen 3 or Zen 4 chiplets where AMD's Ryzen CPUs really hit their stride.

There's another minor change from the previously published specifications on the RX 7900 XT. When first announced, AMD listed a 300W TBP (Total Board Power) rating, but it has since increased that to 315W. It says it found there was a decent increase in performance for a relatively minor bump in power use.

Finally, let's talk pricing and potential performance. We weren't particularly happy with Nvidia's "step down" RTX 4080 ushering in higher prices on the xx80 model GPUs, but AMD's RX 7900 XT is arguably just as bad. On paper, it has 17% less memory and memory bandwidth, and 16% less computational performance. That's fine on its own, but the price savings are only 10%. In other words, just like the RTX 4090 may actually be the better "deal" from Nvidia, we think most people eyeing the RX 7900 XT will be better off spending an extra $100 for the XTX model. 

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