AMD Radeon RX 7900 XTX and XT with RDNA3 chipsets against GeForce RTX 4080

The two new Radeon graphics cards RX 7900 XT and RX 7900 XTX should be available from December 13th – from AMD as a reference design and from the board partners. AMD’s recommended retail price is $999 for the RX 7900 XTX with 24 GB of GDDR6 graphics memory and $899 for the weaker RX 7900 XT with 20 GB. Then there is the value added tax, so that higher prices of at least 1210 or 1090 euros can be expected in Germany, depending on the dollar exchange rate. Given the differences in specifications and the assumed difference in performance, the difference in price is too small, the RX 7900 XT too expensive.

Gaming performance in high definition

With up to 61.6 TFlops of computing power at a 2505 MHz boost clock and revised architecture (see below), AMD 4K gamers see the new Radeon as well equipped. So far, however, AMD has only announced relative performance values ​​​​compared to the RX 6950 XT for the Radeon RX 7900 XTX. In games with an Ultra HD resolution of 50 (“Call of Duty Modern Warfare II”, “Watch Dogs Legion”) to 70 percent (“Cyberpunk 2077”) it is said to be faster than its predecessor. If ray tracing is used, the lead is only 50 (“Resident Evil: Village”, “Metro Exodus Enhanced”) to 60 percent (“Doom Eternal”), in individual cases like “Dying Light 2: Stay Human” including upscaling technology FidelityFX Super Resolution (FSR) but up to 85 percent.

Otherwise, concrete performance information was only available with the upscaler FSR, which significantly increases the image rate but reduces the image quality. Nvidia had already proceeded in a similar way when introducing the RTX 4000 graphics cards, where numbers without the FSR competitor DLSS were also scarce.

With the values ​​mentioned, the RTX 4090, which costs around 2000 euros+, should be out of reach, so that the true opponent of the Radeon top models will probably be the GeForce RTX 4080, which will be available on November 16th, needs 320 watts and should cost 1469 euros . Here the comparison should be in favor of AMD, as long as no ray tracing is used.

Radiance: Monitors with 8K and hundreds of Hertz

In the first presentation, AMD draws attention to the display engine called “Radiance” as a unique selling point, which – unlike Nvidia’s RTX 4000 – already meets the DisplayPort 2.1 specification. With 1.35 gigabits per second and lane (54 Gbps in total), it controls 4K screens with 480 Hertz, 8K monitors with 165 Hz. With Nvidia, 240 or 60 Hz is the end. The Radeon RX 7900 XT and XTX have two DisplayPort 2.1 ports and a USB Type-C output, as well as an HDMI 2.1 socket.

With these enormous refresh rates, for which the first monitors are not expected before 2023, AMD wants to specifically target e-sports enthusiasts. In “Valorant”, “Overwatch 2” and “Apex Legends” you can reach the frame rate limits at 833, 600 and 300 fps with “e-sports settings” (1440p, medium and low details) according to AMD.

AMD doubles the media engine so that it can work on two streams at the same time. The hardware now also decodes and encodes AV1 videos, which leads to better picture quality, especially at low bit rates.

Navi31 with 7 graphics chips

The heart of both graphics cards is the Navi31 MCP or multi-chip package. It combines the central, 300 mm² graphics compute chip, which includes the execution units, the command processor and the media and display engine, with six 37 mm² small memory cache dies. These each provide 16 MB, so together up to 96 MB Infinity cache and are manufactured in the proven 6-nanometer process from TSMC. TSMC manufactures the graphics compute chip in the newer 5 nm process.

The memory subsystem including 96 MB Infinity Cache is said to work up to 2.7x as fast as the RX 6950XT and achieve a combined read/write throughput of 5.3 TB/s, of which 960 GB/s is attributable to the GDDR6 memory . For comparison: Nvidia’s L2 cache on the GeForce RTX 4090 has been able to elicit 2.7 TB/s so far.

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The 96 compute units get a new structure, but AMD is currently still saving on details. If possible, the two groups of two times 32 shader ALUs are supplied with several commands (VLIW2), which can increase the throughput. To do this, however, the shader compiler must extract instructions from the data stream that can be processed in parallel (instruction level parallelism, ILP). If he doesn’t do that, performance falls by the wayside. In addition, there is 50 percent more register memory, which all execution units have to share, however, so that it could sometimes be tight here.

For the ray tracing units, AMD has integrated support for DXR Ray Flags and increased the throughput and the execution window by 50 percent. The box sorting and ray traversal functions have also been revised.

There are also two AI engines that can handle an 8-bit integer format and bfloat16 and, according to AMD fellow Sam Naffziger, are designed for gaming use but not for general calculations. There are currently no plans to control them separately via API so that developers can use them themselves. Rather, they are probably clamped in by AMD’s FSR 3 with AMD Fluid Motion Frames, which, like Nvidia’s DLSS 3, should insert artificially generated frames between the rendered images (frame generation) – but AMD did not want to give any details yet.

externals

AMD provides a 2.5-slot cooler with three axial fans in the reference design, similar to the Radeon RX 6800/6900 XT. With a length of 287 millimeters, they are 11 millimeters longer, but still fit in most gamer cases.

Both cards have a PCIe 4.0 x16 connector and are supplied with additional power from the power supply via two conventional eight-pin plugs. The total board power, i.e. the maximum expected, permanent power consumption, is 355 watts for the Radeon RX 7900 XTX and 300 watts for the XT version. On paper, the top model is therefore significantly more frugal than Nvidia’s flagship GeForce RTX 4090, which consumes 450 watts.

(csp)