AMD explains how the new 3D V-Cache improves over the original

In context: AMD launched the Ryzen 9 7950X3D on the finish of final month and welcomed an enthusiastic response to its second-gen 3D V-Cache regardless of some combined opinions about its usefulness in a 16-core CPU. Now they’ve shared among the technical particulars that designate its efficiency.

AMD began mixing nodes in 2019 when it used the 7 nm node for the core complicated die (CCD) and the 12 nm node for the IO die of the Zen 2 microarchitecture. AMD just lately confirmed to Tom’s Hardware that Zen 4 steps it as much as three nodes: the 5 nm node for the CCD, the 6 nm node for the IO die, and the 7 nm node for the V-Cache.

AMD defined among the challenges it confronted stacking one node onto one other throughout its current ISSCC presentation. Both the 7950X3D and the unique 5800X3D have their V-Caches positioned over their common L3 caches to permit them to be linked. The association additionally retains the V-Cache away from the warmth produced by the cores. However, whereas the V-Cache suits neatly over the L3 cache within the 5800X3D, it overlaps with the L2 caches on the perimeters of the cores within the 7950X3D.

Part of the issue was that AMD doubled the quantity of L2 cache in every core from 0.5 MB in Zen 3 to 1 MB in Zen 4. But it labored across the extra house constraints by punching holes by means of the L2 caches for the through-silicon vias (TSVs) that ship energy to the V-Cache. The sign TSVs nonetheless come from the controller within the heart of the CCD however AMD tweaked them too to cut back their footprint by 50%.

AMD shrunk the V-Cache down from 41 mm2 to 36 mm2 however maintained the identical 4.7 B transistors. TSMC fabricates the cache on a brand new model of the 7 nm node that it developed particularly for SRAM. As a outcome, the V-Cache has 32% extra transistors per sq. millimeter than the CCD regardless of the CCD being manufactured on the a lot smaller 5 nm node.

All of the refinements and workarounds AMD applied add as much as a 25% enhance in bandwidth to 2.5 TB/s and an unspecified enhance in effectivity. Not unhealthy for 9 months between the primary and second generations of a supplemental chiplet. Hopefully it exhibits its worth when the Ryzen 7 7800X3D arrives in a month’s time.


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