After teasing its 256-core Epycs for more than a year, AMD is finally ready to talk about architectural changes to the Zen core that not only make it possible, but will eventually power its next generation of Ryzen processors in desktop and mobile PCs. During a press event in Las Vegas last week, AMD spilled the beans on its latest Zen cores, which promise an average 27 percent uplift in instructions per clock (IPC) across a variety of AI and server workloads, along with boosted clocks ranging from 4. 1 to 5. 3 GHz. We expect to see even higher frequencies on consumer chips before long, but AMD isn’t quite ready to talk about Ryzen just yet. CPU performance is a function of power, IPC, and clocks, and with gains across all three, the cores are shaping up to be one of the company’s biggest generational jumps ever. A tale of two cores
As in past Epyc launches, Zen 6 isn’t one core. It comes in two flavors: a frequency-optimized variant (Zen 6) and a density-optimized version (Zen 6c). This split dates back to the launch of AMD’s Bergamo Epycs in 2023, which packed 128 compact Zen 4c cores into just eight chiplets. The chip’s debut drew comparisons to Intel’s still relatively new Efficient (E-cores) for obvious reasons. But under the hood, AMD’s Zen 4c was nothing like what Intel was doing. The core itself was nearly identical to Zen 4; it simply traded clocks and a bit of cache per core for a more densely packed CPU die. The only difference between running an application on Bergamo or Genoa was how quickly it executed. The same could not be said of Intel’s P and E cores, which used different ISAs. This remained a defining characteristic and advantage of AMD’s compact core architecture through Zen 5, which allowed it to ship Turin parts with up to 192 cores without users having to worry about whether their app was running on a compact core or not. With Zen 6c, at least as we understand it, this philosophy is largely unchanged. Both Zen 6 and Zen 6c share the same ISA, with clock being the main differentiator. There are other micro-architectural differences between the two cores designed to balance IPC and clock speeds more effectively. Looking at the core’s block diagram, this isn’t immediately obvious. Zen 6 and Zen 5 share a very similar front and backend. We’d be tempted to call the core iterative if it weren’t for the 20 to 31 percent IPC uplift for cloud and AI workloads that AMD claims over Zen 5. This suggests that core for core, a 4. 1 GHz Zen 6c-based Venice Epyc should deliver performance on par with a Zen 5-based Turin Epyc running at 5 GHz. That’s a pretty sizable jump, but just because AMD is seeing generational performance uplift in enterprise server and cloud workloads doesn’t mean we’ll see the same gains on the client side. Many will recall the roughly 5 percent performance gains gaming PC enthusiasts reported with the Ryzen 9000-series, leading to the rather unfortunate turn of phrase "Zen 5 percent." That happened because game engines at the time simply weren’t CPU-bottlenecked, and so faster cores could only raise the ceiling so much. Even so, AMD fellow and "Zen daddy" Mike Clark tells El Reg that PC buyers expect more than a 6 percent gain from Zen 6. We’re glossing over a bunch of low-level architectural optimizations here, but according to Clark, one of the biggest drivers of performance was to the front end…