A Ryzen 9 5900X3D engineering sample has unexpectedly broken cover on Chinese forums, providing us with a glimpse of the AM4 processor that never escaped AMD labs. While the firm had previously demonstrated prototypes with 192MB of L3 cache, this chip notably follows the same 128MB design we’d see on AM5 successors.
Chiphell forum user 灵乌路空 stopped short of sharing actual photographs of the engineering sample, but has shared screenshots of the processor running on an AM4 motherboard. However, reaching that point took some work as the chip refused to boot with newer BIOS versions, requiring a cycle back to firmware version 56.70.0. This isn’t too surprising given the 5900X3D never saw the light of day, so there is no need to waste firmware space for it, particularly on a space-constrained 16MB BIOS chip.
Like the Ryzen 9 9900X3D and 7900X3D that would succeed it, this 5900X3D engineering sample sports two CCDs with six cores a piece, for a total of 12 cores with 24 threads. Furthering the similarities between the three generations of CPU, 3D V-Cache only presents on one CCD, meaning the 128MB pool splits between 96MB (32+64MB) and 32MB stacks.
Screenshots reveal that this 5900X3D engineering sample is capable of reaching frequencies ~4.7GHz, around 100MHz below the 4.8GHz that the Ryzen 9 5900X delivers. Such a shortfall is within expectations, as the Ryzen 7 5800X3D (4.5GHz) exhibits the same difference between the 5700X (4.6GHz). The reason for this is because the 3D V-Cache layer sits on top of the core die, hindering their ability to cool and thus to reach higher clock speeds. CPU-Z also listed a 105W TDP, which is identical to the non-X3D variant.
We’ll never know exactly how much AMD would’ve charged for this CPU. Giving our best guess, a potential 5900X3D likely would’ve slotted between the $549 Ryzen 9 5900X and the $799 Ryzen 9 5950X. It’s a shame we never got to see such a setup realised with Zen 3 cores, but this engineering sample provides an interesting sneak peek at what could have been.
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