A while back, we reported that AMD’s higher-end RDNA 4 GPUs had been canceled. That seems to be the case, leaving the next-gen Radeon family with monolithic, midrange dies. A leak from Moore’s Law is Dead showcases the Navi 4C GPU, which was allegedly going to be the Radeon RX 8900 XTX. We’re looking at a highly modular design with up to 14 disaggregated dies packaged using TSMC’s 3D stacking CoWoS technology.
Above the substrate, we’ve got three AIDs (Active Interposer Dies) and one MID (Multimedia and I/O Die) connected using the CoWoS-L silicon bridge. The substrate and interposer dies are linked using standard C4 bumps. The MIDs are the equivalent of the MCDs (Memory Complex Dies) found on the Navi 31-powered Radeon RX 7900 series GPUs. They house the memory controllers, L3 cache, and other I/O components.
The SEDs (Shader Engine Die) are the most interesting bits of Navi 4C (Navi 41). These are small Graphics Compute Dies distributed across the AIDs in groups of three. Each Interposer Die holds three SEDs 3D stacked atop it and powered using CoWoS-V TSVs. The fully enabled RDNA 4 flagship would pack up to 9 Shader Dies, although the RX 8900 XTX would probably disable a few.
Although an ambitious design, this results in a highly complex structure with several chokepoints. Gaming GPUs are highly sensitive to latency, often resulting from a lag caused when two or more disaggregated components communicate and move data among them. Synchronizing all these shader units would be a highly complex task which is likely why the Radeon RX 8900 XTX was scrapped along with Navi 4C.
AMD overcame the latency issue with the MCDs on the Radeon RX 7900 series graphics cards by increasing the speed of the Infinity Fabric linking them to the GCD. Doing the same with multiple compute or shader dies will be much more complicated as they feature much faster components (L1, L2, vGPRs). This is also the reason why NVIDIA’s next-gen RTX 50 series “Blackwell” GPUs will also be monolithic.
