256GB (4x64GB) DDR5 Overclocking Results w/ 9950x and MSI MAG X670E Tomahawk

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So while in my local Microcenter to buy a 9950x + MSI Mag X670E + RAM bundle the other day, I noticed that they had a few 2x64 kits of Corsair DDR5 on sale for $260 each ( Crucial Pro 128GB Kit (2 x 64GB) DDR5-5600 PC5-44800 CL46 Dual Channel Desktop Memory Kit CP2K64G56C46U5 - Black - Micro Center ). Being curious to see if I could even POST with 256GB of RAM, let alone OC it, I picked up 2 of the 3 kits they had and brought them home to see how far I could go.

Here’s the relevant parts of the build: Part List - AMD Ryzen 9 9950X, 2 x GeForce RTX 3090, Phanteks Eclipse P600S ATX Mid Tower - PCPartPicker

I fully updated bios and drivers before trying anything so I’m now running MSI’s 7E12v1H bios with AGESA PI-1.2.0.3a Patch A.

They POSTed after memory training for like 5 minutes, and were running at 3600 MT/s by default:

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To start overclocking, I made the following changes in bios:
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With 1.3V and resistances tuned down to 30/40ohms I was able to walk the memory speeds all the way up to 5000 MT/s:

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Did some brief (few minutes) stress testing and nothing exploded but I didn’t run 24hour stability tests to verify if the memory was holding up long term. I tried messing with settings (more voltage, intentionally loosening subtimings) to try and POST above 5000MT/s but have so far seen no success… If anyone has any ideas of where I could go from here to try and push closer to 6000 MT/s I’m all ears, otherwise I thought I’d leave this here in case folks are curious in the future about what can be done with 256GB on AM5.

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I currently have my 4x64GB CUDIMM kit from kingston running at 4800MHz. It passed memtest, but I haven’t tried anything else with it.

Will try to copy your configs and see how it goes :stuck_out_tongue:

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CUDIMMs on an AMD motherboard?

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Those were not CUDIMMS. just normal DDR5 UDIMMS

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It works on bypass mode, but only for the 9000 series. 7000 series won’t post at all.

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So I think I could get to 5200 or 5400 MT/s with 256GB but not the EXPO speed of 5600 for these kits or my goal of 6000 MT/s. So I started testing 128 (2x64) speeds and with one of the two kits I was able to POST at 6000MT/s and CL42:

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CL40 didn’t POST but I could probably tighten the timings a bit more with some more testing time. Note, I could NOT post at 6000 MT/s with the other kit so YMMV.

Given that I have no actual use case for 256GB on my home workstation I’m going to return the slow kit and keep the one that I could get to post at 6000 MT/s. With Crucial selling this kit at $260 its pretty competitive with 2x48GB kits at the same speeds (I see $220 for the cheapest 5600MT/s 96gb kit on Newegg).

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I installed this same kit recently on a new B650/Phoenix 1 build and I spent a good deal of time tuning. It seems to be passing every memory test for long durations at 6200 MT/s. I have a thread here detailing the build, “128 GB AM5 for the Global South”. I’ll post my tuning details and methodology there soon.

Main timings are 40-44-40-70-114-48-18-12 (tCL-tRCD-tRP-tRAS-tRC-tWR-tWTR-tRTP).

Suggestions:

  1. Try lowering memory voltages (VDD, VDDQ, VDDIO). 1.15 - 1.2 V worked for my kit, higher voltages were actually less stable.
  2. Try tightening up those timings. Performance could improve equivalent to roughly 400 MT/s with optimized primary and secondary timings.
  3. I believe raising VSOC to 1.25 will help with IMC performance.
  4. Don’t let your SOC temps get too high, this affects IMC stability.
  5. Watch your DRAM temps. I have a 70mm fan blowing over the modules from the top edge of the board, which is normally off but spins up when RAM is under load. Module sensors stay under 40C even under long duration memory test loads.

6400 MT/s also posted, but errored quickly during testing. I think the IMC of my CPU was just not cutting it with a 1:1 MCLK:UCLK. I’d like to try 2:1 at some point.