Besides more RAM, 3970x also has proper ECC support.

And more PCIe lanes, compared to the consumer platforms with a measly 20/24 (which is basically one GPU and one NVMe full bandwidth).

How is the ECC support deficient on later CPUs? I checked the docs, it does seem to be supported on the 7000x series.

The CPU is alright, but the motherboards are lacking. You can install ECC memory modules on them and the system will boot, but you don't know for sure if ECC is really working unless the motherboard reports memory status like how many errors were correct. Someone mentioned on HN that there's a Linux kernel component for this and that he had luck with an ASRock motherboard.

Keep in mind that 128 GB barely works on AM5 (basically, EXPO/XMP doesn't, only regular JEDEC speeds, i.e. 4800 MT/s) [1] 2 sticks of RAM up to 64 GB is the fully functional maximum.

[1] https://old.reddit.com/r/Amd/comments/xzj69v/is_anyone_runni...

Are you saying that 2x32GB is the max that allows for EXPO/XMP? I'm thinking about building a system like that and this is critical. Do you have any better resources that explore this more and test out different configurations?

That's my understanding, yes. All my knowledge is from random Reddit threads however.

Since I was scared off 128 GB by all those complaints, I built a 7950X system with 2*32GB memory, and it runs well/stable at its rated 6000 MT/s with EXPO on (also, AMD says 6000 MT/s is the sweet spot for AM5 memory interface, so I am happy).

Motherboard: ASRock X670E Steel Legend

RAM: G.Skill Trident Z5 Neo 64 GB (2 x 32 GB) DDR5-6000 CL30

Here is another thread I remember reading: https://old.reddit.com/r/hardware/comments/za0x0q/level1tech...

That's what I got (7950x steel legend), except that I'm running 128GB memory at 4800.

Here's my stream results (with the cpu in 105watt "eco" mode):

  $ wget https://www.cs.virginia.edu/stream/FTP/Code/stream.c
  $ gcc -O3 -fopenmp stream.c
  $ a.out

  Number of Threads counted = 32

  Copy:           45571.7
  Scale:          40672.0
  Add:            45317.3
  Triad:          42759.0

With array size 8,000,000

  Copy:           31551.3
  Scale:          30983.7
  Add:            34403.6
  Triad:          34484.1

Interesting, didn't think memory speed will make so much difference but it did.

7950x X670E Steel Legend, standard mode, 2*32 GB = 64 GB RAM at 6000, CL 30.

    Array size = 1,000,0000

    Copy:           61488.8
    Scale:          55905.4
    Add:            61320.2
    Triad:          57706.5

    Array size = 8,000,0000

    Copy:           43631.0
    Scale:          43062.7
    Add:            46782.6
    Triad:          46966.8

Wow, that's significant. I may have to look into that.

Running with two DIMMs per channel is more challenging for the CPU's memory controller than one DIMM per channel, and it's much worse if they're dual-rank DIMMs—which current 32GB DDR5 modules are. I believe the EXPO/XMP profiles are all based on using only two DIMMs total, because those modules are sold in kits of two. At some point in the next year, there should be 24GB single-rank modules hitting the market, allowing for 48GB at top speed or 96GB with less of a performance penalty than 128GB from 4x32GB currently causes.

I can't max out my PCI slots and run 256gb in quad channel, though.