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Comment by ciupicri | Hacker News Reader

Right now the problem with consumer grade CPUs from AMD is that you can't have 128 GB of memory running at full speed. You need to use 4 memory modules which means a lower speed. From https://www.amd.com/en/products/cpu/amd-ryzen-9-7950x

    Max Memory Speed
    2x1R    DDR5-5200
    2x2R    DDR5-5200
    4x1R    DDR5-3600
    4x2R    DDR5-3600

There's also the issue of ECC.

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Micron is talking up 128gb sticks, coming semi-soon-ish. https://www.anandtech.com/show/21077/micron-samples-128-gb-m...

And limited PCIe lanes.

Though theoretically that will stop being an issue when it’s viable to only hand the gpu 4-8 pcie 5.0 lanes and 1-2 lanes to an nvme drive or two. Then there would be plenty left over for other things.

100%, still rocking the original 1950x for this reason alone. More nvme storage makes a bigger difference to me than more cores or ipc. Pcie is where all the fun things are used =)

Huh, I didn’t know this. I recently upgraded my workstation to 128G and after some trial and error had to bring down the memory speed from 6000 to 4800.

Is it working just by accident?

CPU: AMD Ryzen 9 7950X Memory: GSkill Trident Z5 Neo 6000 MHz. Mobo: Asus Tuf Gaming x670e WiFi 6e

> Is it working just by accident?

Probably a case of "not exactly". You're just overclocking the memory, and both your memory modules + the rest of the system are happy with those particular speeds.

It'll probably run happily at those speeds basically forever, so nothing to really worry about from doing that.

you can at least get 96GB now, with 48GB dimms

But not with ECC, unfortunately. At least not yet, but I haven’t heard of any in the pipeline.

> There's also the issue of ECC.

Does something prevent Zen 5 CPUs from using ECC memory?

Or maybe you mean that ECC puts more load on the memory controller, potentially reducing top RAM speed compared to non-ECC configurations?

From an old article published by Puget Systems in 2013 [1]:

> Finally, ECC RAM is slightly slower than non-ECC RAM. Many memory manufacturers say that ECC RAM will be roughly 2% slower than standard RAM due to the additional time it takes for the system to check for any memory errors. To verify this, we examined multiple benchmarks that we run on each system we produce. By using comparable CPUs (For example: Intel Core i7 4771 3.5GHz Quad Core 8MB versus Intel Xeon E3-1275 V3 3.5GHZ Quad Core 8MB) we found that this 2% estimate to be roughly correct. Our own benchmarks showed a performance hit ranging from .72 to 2.2% which, given normal testing deviations, is right in line with the 2% estimate.

[1]: https://www.pugetsystems.com/labs/articles/Advantages-of-ECC...

I wasn't commenting on the speed of ECC memory, although from what I've seen manufacturers don't offer ECC memory modules with a speed as high as non-ECC versions.

Anyway what bugs me about Zen < 4 is that you can install ECC memory, but you can't be sure that ECC is really working on some motherboards.

For Zen 4 at least there's DDR5 with its on-die ECC, but the path to the CPU might still be unprotected.

> manufacturers don't offer ECC memory modules with a speed as high as non-ECC versions.

Indeed, they seem to be aiming their ECC sticks at the server market, their "overclockable" sticks at the gamer market, and not mixing the two. Perhaps this would change if more workstation motherboards officially supported ECC.

In the meantime, I suspect today's ECC RAM and X3D cache CPUs might complement each other well.

> For Zen 4 at least there's DDR5 with its on-die ECC, but the path to the CPU might still be unprotected.

Some Zen 4 motherboards do support ECC. ASUS lists it in their manuals and exposes settings for it in their EFI setup, for example.

As for being sure that it's working, I suppose that depends on the OS. This addition in Linux 6.5 looks helpful:

https://www.phoronix.com/news/AMD-EDAC-Ryzen-7000-Series

You can most certainly test ECC functionality on unqualified boards using a Linux LiveCD/USB. And there are plenty of boards that have gone through the process of getting ECC qualified, and advertise the feature. ASUS, for instance.

I assume you're also still limited to dual-channel in both scenarios?

From the same page:

    Memory Channels: 2

On the other hand the specifications for Threadripper™ PRO 5945WX [1] say:

    Memory Channels: 8

[1]: https://www.amd.com/en/products/cpu/amd-ryzen-threadripper-p...

Oof

Are you ignoring EXPO?

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