Architecture

The Radeon RX 7800 XT and RX 7700 XT debut the new Navi 32 silicon, as part of AMD's desktop-first approach to the RX 7000 series. This is a chiplet-based GPU, just like the Navi 31 which powers the RX 7900 series, but scaled down. The centrally located graphics compute die (GCD) is based on the newer 5 nm EUV foundry process, and contains the main number crunching machinery of the GPU, all the stuff that tangibly benefits from the switch to the newer node, while the Infinity Cache and GDDR6 memory controllers—things that don't benefit as much from 5 nm, are spun off as chiplets called memory cache dies. Navi 32 gets four such MCDs compared to six on Navi 31. Each of these has a 16 MB segment of the GPU's 64 MB Infinity Cache, and a 64-bit portion of that adds up to its 256-bit GDDR6 memory interface.

The 5 nm GCD features 60 RDNA 3 compute units, each worth 64 stream processors, which works out to 3,840. This is a 50% generational increase in shaders compared to Navi 22 powering the Radeon RX 6700 series, but is a reduction when compared to the RX 6800 XT that's equipped with 72 RDNA 2 compute units. AMD is counting on the increased IPC, higher engine clocks, and greater memory bandwidth of Navi 32 to come through and make the RX 7800 XT faster than its predecessor; although given its pricing, AMD considers the RX 7800 XT to succeed the RX 5700 XT, and prove to be a viable upgrade for all those who held out on the RX 6000 series over the last three years.

The Radeon RX 7800 XT maxes out the Navi 32 silicon, enabling all 60 CUs, which work out to 3,840 stream processors, 120 AI accelerators, 60 Ray accelerators, 240 TMUs, and 96 ROPs. With all four MCDs enabled, the RX 7800 XT gets 64 MB of Infinity Cache, and a 256-bit GDDR6 memory interface, which it puts to good use with 16 GB of memory—same amount as the RX 6800 XT. The GPU runs at 2124 MHz Game clock, with 2420 MHz boost, however within this band internally, the front-end of the GPU runs at 10-15% higher clock speeds than the shader engines. The memory runs at 19.5 Gbps, which gives the RX 7800 XT a handy 628 GB/s of memory bandwidth.

The Radeon RX 7700 XT is cut down from the Navi 32 silicon, enabling 54 out of 60 CUs, giving it 3,456 stream processors, 108 AI accelerators, 54 Ray accelerators, 216 TMUs, and 96 ROPs. This SKU has three out of four MCDs enabled, which gives it 48 MB of Infinity Cache, and a 192-bit GDDR6 memory interface that is uses for its 12 GB of memory size. AMD runs the GPU at higher clock speeds than the RX 7800 XT, with 2171 MHz game clocks, and 2544 MHz boost. The memory is slightly slower, at 18 Gbps, giving it 432 GB/s of memory bandwidth.


Much of the architectural innovation is this generation is with the RDNA 3 Dual-Compute Unit (or Compute Unit pair). The "Navi 32" GPU physically features 60 compute units spread across three Shader Engines. AMD claims that at the same engine clocks, the RDNA 3 CU offers a 17.4% IPC increase over the RDNA 2 CU.


The new RDNA 3 CU introduces multi-precision capability for the 64 stream processors per CU: operating either as 1x SIMD64 or 2x SIMD32 units. The Vector Unit that houses these SIMD units can either function as a SIMD execution mechanism, or as a Matrix execution unit, thanks to the new AI Matrix Accelerator, which provides a 2.7x matrix multiplication performance uplift versus conventional SIMD execution. Also added are support for the Bfloat16 instruction-set, and SIMD8 execution. The GPU hence enjoys AI hardware-acceleration that can be leveraged in future feature-additions relevant to gamers. Game developers will also look for ways to exploit accelerated AI, now that all three brands feature it (NVIDIA Tensor cores and Intel XMX cores).


AMD's first-generation Ray Accelerator, introduced with the RDNA 2 architecture, was the result of a hasty effort to catch up to NVIDIA with a DirectX 12 Ultimate GPU, where they developed fixed-function hardware to calculate ray intersections, and offloaded a large chunk of RT processing to the generationally-doubled SIMD resources. With RDNA 3, they've refined the Ray Accelerator to achieve an 80% ray tracing performance uplift over the previous generation, when you add up the Ray Accelerator count, their higher engine clocks, and other hardware-level optimizations, such as early sub-tree culling, specialized box sorting modes, and reduced traversal iterations.


There is a 50% ray intersection capacity improvement for RDNA 3 thanks to these optimizations, and cycles-per-ray reduction. Besides these, AMD has also made several improvements to the geometry- and pixel-pipes, with the introduction of the new multi-draw indirect accelerator (MDIA), which reduces CPU API and driver-level overheads by gathering and parsing of multi-draw command data. At the hardware-level 12 primitives per clock is now supported compared to 8 per clock on RDNA 2, thanks to culling. The core-configuration overall enables 50% more rasterized performance per clock.


AMD has significantly improved the Display Engine of "Navi 32" over the previous-generation in terms of connectivity. The new Radiance Display Engine comes with native support for DisplayPort 2.1, which enables 8K output at up to 165 Hz refresh-rate, or 4K at up to 480 Hz, with a single cable. AMD has refined its FSR 2 algorithm to support 8K (i.e. render at a lower resolution with FSR-enhanced upscaling), to make it possible to enjoy the latest AAA titles at playable frame-rates on 8K displays. The RX 7800/7700 XT gets two full-size DP 2.1 connectors, besides an HDMI 2.1b, and a USB-C with DP 1.2 passthrough. The "Navi 32" silicon receives full hardware-accelerated AV1 encode and decode capabilities. With this generation, AMD is also introducing SmartAccess Video, a feature that lets the AMD driver leverage the hardware encoders of the RDNA 2 iGPU of Ryzen 7000 desktop processors, for additional encoding performance.

FidelityFX SuperResolution 3 Fluid Motion Frames (FSR 3 and FMF)

As part of the Radeon RX 7800 XT and RX 7700 XT announcements, AMD finally announced the much awaited FidelityFX Super Resolution 3 and Fluid Motion Frames. FSR 3 is being announced as a technological rival to NVIDIA DLSS 3 Frame Generation. The premise with both technologies is the same—to effectively double frame-rates by generating alternate frames without running them through the entire graphics rendering pipeline, it's just that the two technologies differ in their approach to this goal.

FSR 3 builds on FSR 2 with its updated super resolution upscaler promising generational quality improvements at a every given rendering resolution. Fluid Motion Frames (FMF) isn't the entirety of the FSR 3 feature-set, but is its most important feature-addition. FMF is a frame interpolation technology much like the one consumer televisions come with. Alternate frames are generated as an approximate of two frames. Where FMF differs from DLSS 3 Frame Generation is that while NVIDIA uses a hardware component called optical flow accelerator and the GPU's AI acceleration to generate an intermediate frame without involving the graphics rendering pipeline, FMF uses a certain amount of the graphics rendering pipeline. At a hardware level, FMF uses the main SIMD machinery of the GPU, leveraging asynchronous compute. As with DLSS 3 FG, FSR 3 FMF comes with added latency. NVIDIA counteracts this with Reflex, while AMD uses Radeon AntiLag+. Both technologies try to keep the frame queue short to reduce whole system latencies.

One major advantage FSR 3 FMF enjoys over DLSS 3 FG is that it works on any modern DirectX 12 GPU that supports async compute, since it doesn't require a specific hardware component the way DLSS 3 FG requires the Optical Flow Accelerator on NVIDIA "Ada" GPUs. The only limiting factor here is the performance. To be more specific, AMD says that all Radeon GPUs from RX 5700 series onward; and all GeForce GPUs from RTX 20-series onward, should support FSR 3 FMF. Also, FSR 3 FMF is as easy to integrate with games as FSR 2 is. The first games implementing FSR 3 FMF should arrive in Fall 2023. AMD is also working to extend FMF to Radeon Super Resolution, the driver-level technology that enables performance upscaling to even games that don't support FSR.

HYPR-RX

HYPR-RX is an interesting new feature AMD plans to integrate with the AMD Software (control center) application. It is a one-click performance boosting technology that works with any DirectX 11 or DirectX 12 game. The software is a cocktail of Radeon Boost, Radeon AntiLag+, and Radeon Super Resolution, and applies the three features on any running game as needed, automatically. Radeon Boost improves performance by dynamically reducing the render resolution of a game when there's too much motion on the screen (and hence not enough detail needed). Radeon Super Resolution improves frame-rates as it applies FSR on the output of a game rendered at a lower resolution (including the frames lowered in resolution by Radeon Boost. AntiLag+ counteracts the latency added by these two, by shortening the frame queue. AMD said that it is working to integrate FMF into the HYPR-RX feature-set.