Introduction

Just a few weeks ago, AMD debuted the Zen 5 CPU microarchitecture and the Ryzen 9000 series Granite Ridge desktop processors. We've reviewed each of the four models the company launched, so be sure to check them out for additional context and background. In this article, we will investigate how the new AMD Zen 5 processors behave with popular memory speeds—both standard and overclocking. AMD processors have good, modern, memory support—the Ryzen 9000 series can handle up to 256 GB of dual-channel DDR5 memory, just like the competing Intel processors. You can drop in any PC DDR5 UDIMM memory kit ever made, and it will just work on Ryzen, albeit at JEDEC-standard speeds. Where AMD and Intel diverge a little is the way they handle memory overclocking, with the two platforms each having a handful of unique settings.



The adoption of DDR5 memory on modern platforms has brought significant advancements in bandwidth and data transfer rates, and AMD's Ryzen 9000 AM5 platform is no exception. As DDR5 memory becomes more mainstream, the potential for performance scaling across various memory speeds offers an opportunity to understand how different configurations impact overall system behavior. In this review, we investigate the scaling of DDR5 memory on Ryzen 9 9950X, running speeds from DDR5-8000 down to the JEDEC baseline specifications of DDR5-5600 and DDR5-4800. These tests aim to highlight the performance gains and any potential trade-offs when pushing DDR5 memory beyond the standard specifications. We're also doing testing at the interesting DDR5-6000 CL28 setting as well as DDR5-6400 with UCLK 1:1.

In this article, we are testing with a Ryzen 9 9950X processor, AMD's fastest Zen 5, with a handful of important memory speeds. To begin with, we run two JEDEC-spec baseline memory speeds of 4800 MT/s and 5600 MT/s—these serve as baseline. Next up, we have DDR5-6000 CL28, which represents AMD's official sweetspot recommendation for these processors, but with tight timings. We also ventured out into DDR5-6400 with 1:1 UCLK to MCLK ratio, which ran perfectly stable on our test system—more on that "ratio" on the next page. Moving up in memory speed we're running DDR5-7200 CL34, which is a typical maximum of the pre-Zen 5 era. Last but not least, we're testing DDR5-8000 CL38, using the wonderful G.Skill Trident Z5 Royal Neo memory kit.

But first some theory. On the following page we'll detail how the memory controller works on AMD's Zen 5 architecture, and why it is quite different to how Intel has been designing their memory architecture. We will also delve into how the memory controller handles high-speed DDR5 memory configurations, assessing potential bottlenecks, thermal behavior, and any adjustments required to maintain stability.