AMD’s secret Zen 3 gaming CPU had 128MB of game-boosting L3 cache but never saw the light of day — canceled Ryzen 9 5900X3D breaks free from the chipmaker's vault

Despite being on the market for four years, the Ryzen 7 5800X3D remains one of the best CPUs for gaming on the AM4 platform. A Ryzen 9 5900X3D, if AMD had released it, would surely have given it a run for its money. Now, years later, an engineering sample of the Ryzen 9 5900X3D has emerged on the Chinese Chiphell forums, giving us a taste of what could have been an awesome 12-core chip for gaming and productivity.

What is really funny about the Ryzen 9 5900X3D is that we all knew it existed because AMD teased it at Computex 2021. The chipmaker showcased a “12-core 3D Chiplet Prototype" outperforming a regular Ryzen 9 5900X by up to 15% in average gaming performance, with both processors fixed at a 4 GHz frequency.

The Ryzen 9 5900X3D engineering sample (100-000000652-20_48/32_Y) brought to light by a Chiphell user reveals 128MB of L3 cache, double the amount found on the standard Ryzen 9 5900X. This comes from AMD integrating 64MB of 3D V-Cache onto one of the two Core Complex Dies (CCDs) inside the chip. The CPU-Z screenshot also shows a 4,649 MHz clock speed, which is likely the boost clock. If so, and rounding the boost clock speed to 4.7 GHz, the Ryzen 9 5900X3D could have launched with a boost clock just 100 MHz lower than the Ryzen 9 5900X.

Intriguingly, the 128MB configuration was just one of several experiments AMD was exploring. During a visit to AMD's labs, Gamers Nexus captured a 12-core Zen 3 chip with a staggering 192MB of L3 cache. It is the result of a Ryzen 9 5900X equipped with 64MB of 3D V-Cache on both CCDs. Another 16-core Zen 3 chip also had a similar 192MB L3 configuration, likely a Ryzen 9 5950X3D if it had come out on the retail market.

AMD Ryzen 9 5900X3D Specifications*

*Specifications are unconfirmed by AMD.

These early 12-core and 16-core Zen 3 X3D prototypes paved the way for the Ryzen 7 5800X3D, a processor that reigned as the gaming king for several years. AMD's decision to ultimately pursue an asymmetric design was spot on for gaming. An eight-core chip like the Ryzen 7 5800X3D delivers exceptional gaming performance and is not burdened by cross-die latency that can arise when stacking 3D V-Cache on both CCDs.

While AMD initially skipped equipping its 12-core and 16-core Zen 3 chips with 3D V-Cache, it eventually did so on Zen 4 and beyond, leading to the introduction of the Ryzen 9 7900X3D, Ryzen 9 7950X3D, and, more recently, the Ryzen 9 9900X3D and Ryzen 9 9950X3D, or even the over-the-top Ryzen 9 9950X3D2.

A dual-stack configuration is very advantageous for productivity workloads, but it wouldn’t do much for gaming. Equipping both CCDs with 3D V-Cache means dealing with cross-die latency and lower clock speeds due to thermal and power constraints, which are significant trade-offs for gaming. Our CPU hierarchy shows this clearly: for example, the Ryzen 9 9900X3D (12 cores, 128MB L3) falls behind the Ryzen 7 9800X3D (8 cores, 96MB L3) in gaming. Or, in another scenario, the Ryzen 9 9950X3D (16 cores, 192MB L3) offers similar gaming performance to the Ryzen 7 9800X3D.

AMD knows what it is doing, and the eight-core, single-CCD design is where gaming is at. This winning formula is clearly embodied in the Ryzen 7 5800X3D and, after it, the Ryzen 7 7800X3D and Ryzen 7 9800X3D, chips that have set the standard for high-end gaming processors.

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