Hacker News Reader

Comment by bmenrigh | Hacker News Reader

The worst thing about consumer (AM5) Zen4 and Zen5 is the I/O die chiplet and memory controller on it. I've heard they're finally going to ship a new I/O chiplet in Zen6 on a much smaller node. Their existing AM5 Zen4/5 memory controller when using both memory channels is terrible. Extremely hard or impossible to get above 3600 MT/s.

Of all the things I'm looking forward to on Zen6, an improved memory controller is at the top of the list.

Edit: and yes, others may say the paltry few PCIE 5.0 lanes is the worst thing about AM5, but that doesn't affect my usage much, and unfortunately I think that's a limitation of AM5 itself rather than the I/O chiplet.

View on HN

It's not too hard to get above 3600 MT/s (I assume what you actually want is to get the uclk above 1800) if you bump the soc voltage, but at default voltages there's no chance. Most people overclocking don't touch the soc rail. I've done it on a few zen4 parts and supposedly there are golden samples that go above 1800 without major soc voltage increases but I've never seen evidence of one. And even with major voltage increases the highest you can really achieve is like 2000 on the uclk which is almost a pointless change in memory bandwidth when ddr5 is like +60% without any shenanigans.

I'm talking about with 4 sticks, not 2.

I've never gotten 4 sticks to pass training, no matter what I change. This is a well-known limitation. Some people, with newer AGESA on certain motherboards, have been able to get 4 sticks above 3600 MT/s but it's not possible for most people, and questionably stable even for those that have succeeded.

I've had no issues on my ASRock X870E Taichi from the very beginning. I'm running four 24 gig sticks at 6000 MT/s (Corsair, all bought before the crazy). I didn't realize people were having this many issues. These are on the certified lists from the manufacturer of the motherboard. Never had a problem. They've been working through multiple AGESA updates / multiple BIOS updates without a hitch.

how ? i have ASRock X870 Steel Legend WiFi and VENGEANCE 6400MT/s CL3 4x32gb and the best i got is 5800 and that was unstable so i run it back at 5000 and even that with slight overclock.

I’m on an MSI x670e with 4x32 sticks, also Corsair. Never gotten training beyond 3600. I’ve recently seen people posting success stories on my same motherboard at 6000 MT thanks to newer bios AGESA. But none of that has worked for me.

X870e is not am4 though. That's ddr5 and a different memory controller.

The initial comment wasn't about AM4.

> Their existing AM5 Zen4/5 memory controller when using both memory channels is terrible. Extremely hard or impossible to get above 3600 MT/s.

Not sure how deep into it you went, but I found with 4 sticks I had to bump soc voltage, memory voltage, and loosen all my timings, especially tRFC. I can only pass training at marginally higher mem clocks with tRFC around 350ns with 4 sticks whereas 2 sticks was down near 200ns. Is it perfectly stable though... I think it's crashed once in the past month? So not perfect but it passed 12-24h of every stress test I could think of, and the one crash was near idle which probably just means my voltages need another bump.

For reference I'm using vsoc 1.08v, vddp 0.98v, vddg 1.0v, vdimm 1.38v and couldn't get above 1900 uclk / 3800 MT/s without uncomfortable vsoc. I've seen lots of people claim 2000/4000 at 1.1-1.15v vsoc but I don't want to run that high daily.

Oh and don't push vsoc to 1.2v+ as per AMD.

I have a 9950X with 4x48G sticks. It is so hard to get it to boot even at 3600. But I persevere to run my local LLMs. I would love to get a new reliable chip for this same motherboard and RAM.

(AM4 was 3600 MT/s; AM5 is 6000 MT/s.)

AM5 is 3600MT/s for 4 sticks; check the specification of a CPU of interest to you, expand the Connectivity section. For 2 sticks it's 5600MT/s. The Ryzen 9 9950x3d officially only supports 5600 or 3600.

https://www.amd.com/en/products/processors/desktops/ryzen/90...

Obviously, you can run memory faster than the officially supported speed, including 4 DIMMS, but the Zen 5 architecture has a reputation for being finicky trying to run 4 DIMMs at higher speeds and you need a bit of care in what you pick and how you tune it.

I'm running 8000 in 2:1 on my 9800x3D. Slightly better than 6200 1:1 on here, and basically the same as 6400 1:1, but easier to dial in at 8000.

Side note: At 2ghz IF, a single Zen4/5 CCD can saturate 7200 MT DDR5, but the io die is not restricted to that, so x16 and IGPU DMA can still saturate it at 8000.

Reported even on AM5, you can only get 6000 Mt/s with 2 sticks, attempting to run all 4 slots on most boards won't work unless you slow them down to base JEDEC speeds.

4 x 32GB G.Skill Flare 6000CL30 are running on Asus TUF B650E with 6000CL34

Can confirm, had this issue on an ASRock DeskMeet X600.

Really? I'm running 4x 24GB sticks at 6000 with no issues. These were on the certified list for the motherboard.

https://valid.cpuid.com/sdyce7k2

Agreed, this is likely going to change the landscape for people ekeing everything out of an AMD-based HEDT.

To take full advantage of it, folks likely will want A) a new motherboard with likely a new chipset to support the higher frequencies and B) <GULP> higher frequency DDR5.

I’d love more memory bandwidth with the limited 2-channels I have, but the 2x48GB (96GB) of “tuner memory” I bought in February 2025 I’m not even sure is manufactured anymore. I paid $440 back then, and my understanding is it’s not produced now, and commands $2500 - $3000 on the second-hand market.

I heard they had issues with the new consumer zen5 I/O die, so unfortunately had to revert to zen4 I/O die for the consumer zen5 CPUs

This is why I love the Ryzen 395 as it has so much more bandwidth than the typical consumer CPU has. Now I would have loved some PCIE 5.0 lanes.

I wonder if this also applies to APUs like the Strix Halo?

Strix Halo has a newer IO die with twice as many memory controllers, and a better interconnect to the CPU dies. I'm not sure if the individual memory controllers are much better than on the Zen4/5 desktop IO die; I don't think I've seen a Strix Halo system built to use desktop DIMMs so testing how it handles two DIMMs per channel isn't practical.

The 9996 in this article has 16 channels for 1.6TB/s and 256 cores/512 threads. Don't know if this will translate to consumer parts.

Reply on news.ycombinator.com