A fresh RDNA 3 rumor has surfaced, this time regarding the mythical Radeon RX 7950 XT. This mega-GPU will reportedly feature a total of 9 chiplets: 2 GCDs (Graphics Compute Dies) and 7 MCDs (Memory Complex Dies). Two Navi 32 GCDs will be paired with 6-7 MCDs, each featuring a 64-bit memory controller and 32MB of L3 cache (16MB x 2-hi stack). This nets a bus width of 448-bit and 222MB of Infinity Cache, if the existing Navi 3x MCDs are reused.
I’m skeptical of these figures as it’s a pretty much non-existent configuration. As such, take them with a grain of salt as they are based on pure speculation. (sunnyflowerdelivery.com) The only bit of confirmed info is with regard to the chiplet count.
Update: It’s possible that the additional chiplets will be 3D stacked atop the existing memory complex dies. However, considering that they are already 2-hi as per Angstromics it seems unlikely. Not to mention that increasing the cache over 200MB will lead to severely diminishing returns. More on that here:
Update 2: It looks like it’ll be a 3D stacked V-Cache variant of Navi 32.
| GPU Name | RX 7700 XT (Navi 33) | RX 7800 XT (Navi 32) | RX 7900 XT (Navi 31) | RX 7950 XT (Navi 30?) |
|---|---|---|---|---|
| Process Node | 6nm | 5nm + 6nm | 5nm + 6nm | 5nm + 6nm |
| Die Config | 6nm x1 | 5nm x1, 6nm x4 | 5nm x1, 6nm x5 | 5nm x1, 6nm x6 |
| Shader Engines | 2 | 4 | 6 | 6 |
| WGPs | 16 | 32 | 48 | 48 |
| CUs | 32 | 64 | 96 | 96 |
| Cores | 4,096 | 8,192 | 10,752? | 12,288 |
| Memory Bus | 128-bit | 256-bit | 320-bit? | 384-bit? |
| Memory Type | GDDR6 | GDDR6 | GDDR6 | GDDR6 |
| Memory Capacity | 8GB | 16GB | 20GB? | 24GB? |
| Infinity Cache | 64MB | 128MB | 192MB | 192MB? |
| TGP | 200W | 250W? | 300? | 350W? |
| Launch | Q4 2022 | Q1 2023 | Q4 2022 | 2023 |
The GCDs will be fabbed on the TSMC N5 5nm process, each packing 8,192 stream processors or cores across 32 256-wide WGPs and 64 128-wide CUs. That results in an overall shader count of 16,384 units, 128 CUs, 64 WGPs, and 8 SEs (Shader Engines). The memory should be somewhere between 24GB and 48GB. Since the bus width is unclear, I can’t really comment on the VRAM size. However, given that the RX 7900 XT will be paired with 24GB, I’m taking that as the baseline. We’ll probably get a clamshell interface, allowing for more flexibility with the memory buffer.
Finally, there’s the matter of the TGP. From what we’ve seen, the Navi GPUs are pretty efficient but powering something as big as this will need over 450W of power. The Radeon RX 7900 XT is slated to land sometime in the last quarter of the year so this behemoth won’t be rolled out anytime soon. A late 2023 launch is plausible.
