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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 reso

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?

skirmish 4y ago
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/level1techs_is_128gb_of_ddr5_impossible_on_am5/ https://old.reddit.com/r/hardware/comments/za0x0q/level1tech...
- injinj 4y ago
  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
  - skirmish 4y ago
    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
    - injinj 4y ago
      Wow, that's significant. I may have to look into that.
wtallis 4y ago
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.

skirmish 4y ago

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/level1techs_is_128gb_of_ddr5_impossible_on_am5/ https://old.reddit.com/r/hardware/comments/za0x0q/level1tech...

injinj 4y ago
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
- skirmish 4y ago
  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
  - injinj 4y ago
    Wow, that's significant. I may have to look into that.

wtallis 4y ago

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.