AMD Talks Zen 4, Demos Killer Stacked 3D V-Cache For 15% Performance Boost

AMD 3D V-Cache
AMD made quite the splash during its keynote at Computex 2021. In addition to launching a new Radeon RX 6000M mobile series based on its RDNA 2 graphics architecture, the biggest surprise came in regards to its processors, and not just what it had to say about Zen 4. AMD CEO Dr. Lisa Su revealed a new stacked 3D vertical cache design that promises to deliver big gains in gaming performance, starting with Zen 3.

What this essentially boils down to is a combination of chiplet packaging, which AMD introduced to its Zen lineup in 2019, and 3D stacking, in collaboration with manufacturing partner TSMC. Dr. Su says 3D chip stacking will drive the future of high performance computing, though more immediately, the first application of this technology is to enable a 3D vertical cache on the Ryzen 5000 series.

AMD Stacked 3D V-Cache

AMD showed off a prototype Ryzen 9 5900X processor with 3D V-cache, which entails stacking 64MB of 7-nanometer SRAM cache directly on top of each core complex die (CCD), to effectively triple the amount of high speed L3 cache that is fed to the Zen 3 CPU cores. The additional cache is bonded directly to the CCD by way of Through Silicon Vias (TSVs), with no soldered bumps of any kind.

To make this feasible, AMD worked with TSMC to thin the cache die and add structural silicon for a seamless surface. The result is that the finished version of the 3D stacked chip looks identical to existing non-3D stacked variants of the Ryzen 5000 series.

The Ryzen 5900X prototype Dr. Su showed off had the lid removed and exposed the left CCD, to highlight the 6mm x 6mm SRAM that is hybrid bonded. In the actual chips that will feature 3D V-cache, 96MB of SRAM cache is bonded to each CCD, for 192MB total in a single package for AMD's 12-core and 16-core Ryzen processors.

AMD Ryzen Gears 5

AMD is pitching this as the most advanced and flexible active-on-active silicon stacking technology in the world. More importantly, AMD touts the benefits of larger caches in many workloads, especially PC gaming. During the presentation, AMD showed off a side-by-side demo of Gears 5, one powered by a regular Ryzen 9 5900X and the other with the same chip, but with the aid of stacked 3D V-cache, both fixed at 4GHz.

The prototype chip netted a 12 percent improvement in Gears 5 on average. And according to AMD, the gains in other games are even better.

AMD Ryzen Gaming Performance

After the brief demo, AMD posted a slide highlighting gaming performance in several other titles, including DOTA 2 (Vulkan), Monster Hunter World (DirectX 10), League of Legends (DirectX 10), and Fortnite (DirectX 12). AMD claims its 3D V-cache nets a 15 percent average performance boost when gaming at 1080p, in those games.

AMD Dr. Lisa Su Tweet

That is a remarkable gain that is about what you get from a generational jump in CPU architectures, yet AMD says it has attained such a boost on its existing Ryzen 5000 series. Impressive for sure, assuming the claims hold up in the real world.

AMD's Zen 4 CPUs Arriving In 2022

AMD's stacked 3D V-cache technology is interesting, and while the prototype it showed off suggests we will see a Ryzen 5000 refresh of some sort, it is a safe bet this will end up in its Zen 4 CPUs as well. To that end, AMD confirmed Zen 4 will arrive in early 2022, though it did not announce a specific release date.

This is true for both the consumer desktop (Ryzen) and server space (EPYC). Beyond the confirmation, we are left to the usual leaks of rumors, of which there are several. For example, Zen 4 is rumored to ditch a pin grid array (PGA) design for a land grid array (LGA) socket, meaning the pins will no longer be on the CPU itself.

Zen 4 is also rumored to deliver at least a 20 percent jump in IPC (instructions per clock) performance. However, the introduction of 3D V-cache could see even higher gains in some situations, at least compared to today's existing Ryzen 5000 series.

You can also expect support for DDR5 memory, though rumor has it AMD will only adopt PCI Express 5.0 support on its EPYC processors, and not its consumer chips.

Buckle up folks, between Alder Lake-S and Zen 4, it's about to become a wild ride.