AMD’s Enthusiast Radeon RX 8000 GPUs Allegedly Featured MCM Navi 4C “RDNA 4” Chips

AMD is alleged to have utilized its Navi 4C "RDNA 4" MCM GPUs to power the next-gen Radeon RX 8000 enthusiast graphics cards.

If you have been reading our recent stories, you may have seen the recent story where it was rumored that AMD canceled its high-end RDNA 4 GPUs. Well, it looks like Moore's Law is Dead might have some additional information on a specific SKU that was meant to be part of the new GPU lineup but was slashed out in favor of more mainstream GPUs.

MLID has posted an alleged diagram of what seems to be a Navi 4C GPU which was to be one of the three Navi 4 configurations based on the RDNA 4 architecture with the other two being Navi 4X and Navi 4M, as disclosed by Kepler_L2 a few months back. The Navi 4C configuration mostly looks to be a very advanced MCM (Multi-Chip-Module) design that utilized various building blocks.

Few more codenames ????

Navi4XNavi4MNavi4C

MI400 Mercury/Venus/Earth

— Kepler (@Kepler_L2) April 18, 2023

The base layer of the AMD Navi 4C (RDNA 4) GPU was the package substrate that would hold multiple AID's and MID's on top of it. The AID is an active interposer die and there are four of those which are accompanied by a single MID or Multimedia & I/O die which was supposed to be similar to the MCD featured on the existing Navi 31 and Navi 32 MCM GPUs. This chiplet included the VRAM bus controllers and the Infinity Cache along with other multimedia capabilities. The MID connected to the AID using a next-gen interconnect fabric and the AIDs were also interconnected to each other using the same fabric.

Now for each AID, there were three SED's layered on top in a stacked chiplet configuration. These SED's (Shader Engine Die) were the main GPU IP blocks performing the shader tasks. The diagram shows that there were at least 9 SED's on this Navi 4C configuration based on the RDNA 4 graphics architecture. The whole package was based on TSMC's COW-V TSV (Chip-On-Wafer) technology and was going to include several configurations but since we don't know about the exact configuration or CU/WGP layout of RDNA 4, it's too early to state what this chip might've been used for. You can also find the mention of SED, AER, and MID's in this patent here which the following diagrams are from:

The leaker states that this specific configuration was expected to be featured on the AMD Radeon RX 8900 XTX which should've been an ultra-enthusiast product since it replaced the 7900 XTX but it looks like that isn't the case anymore and the chiplet design of such a scale isn't ready at least the RDNA 4 generation of GPUs. It is likely that the company didn't meet its targets or expectations with the RDNA 3 lineup and went back to the drawing board to set things straight for future MCM designs.

While this is still a rumor and nothing has officially been confirmed by AMD as of yet, the RDNA 4 lineup is seemingly only going to get Navi 44 and Navi 43 SKUs with the Navi 42 and Navi 41 chips probably out of the equation (for now). The lineup is expected to launch sometime in 2024 so there's still a lot of time left in launch and the company is definitely not done with its RDNA 3 family yet which will be receiving more updates later this fall.

News Sources: Videocardz, Olrak29