Comment by ac29 2 days ago
What goes unsaid in the article is that this will likely only work with Intel's Arrow Lake? Arrow Lake isnt being launched until next month though, so official specs are not available yet. And the full 9600 speed will very likely require overclocking.
It doesnt appear Zen5 can get anywhere close those speeds.
The clock redriver uses a phase locked loop to generate a few identical clock signals for use by the DRAM chips on the module. This same tech is also used for clock multipliers and dividers throughout digital systems.
Rambus has details on their "DDR5 client clock driver" here: https://www.rambus.com/memory-interface-chips/ddr5-client-di...
This anandtech article seems to be a decent summary of what it's doing, the JEDEC JESD82-531A.01 spec is also freely available (with registration) if you're feeling adventurous
https://www.anandtech.com/show/21455/making-desktop-ddr5-eve...
I could see this maybe reducing latency, but wouldn't you still be limited by the memory bus speed regardless of how high you could clock the DDR?
Not an expert, but Zen 5 desktop feels like it is being held back by memory bandwidth. Several tests show there is no real benefit in >6000 DRAMs.
Bandwidth is currently limited by the infinity fabric implementation on consumer AMD CPUs, 6/8 core CPUs with s single CCD top out bandwidth quite early and improvements from higher clocks are minimal even from like 5600, assuming timings are overclocked similarly and beyond basic xmp/expo
> It doesnt appear Zen5 can get anywhere close those speeds.
Looks like it can get to DDR5-8400:
> Finally, we have some absolutely killer RAM. The G.SKILL Trident Z5 RGB series is one of that vendor's top brands, and this is among the top models that it offers. Clocked at a scorching 8400 MT/s with a CAS latency of just 40 cycles, this is the fastest RAM we can reasonably recommend for Ryzen 9000. It comes in the form of a pair of 24GB modules, and using it with Zen 5 could be as easy as just flicking on that XMP switch.
* https://hothardware.com/news/zen5-ddr5-memory-guide
Does that count as "anywhere close"?
I assume the 285K will be able run these at their full 9600?
These are part of a new generation of DDR5 modules that add a clock driver to the module itself, rather than relying entirely on the clock signal coming all the way from the CPU's memory controller. That is expected to significantly change the game for DDR5 overclocking, and expectations based on the limitations of configurations lacking the clock drivers may not be accurate. I expect we'll see 6+ months of firmware tuning before we have a clear picture of what each platform is ultimately capable of, but early on the focus will be on Intel platforms.