Author Topic: RAM clock with full channels  (Read 156 times)

emc2

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RAM clock with full channels
« on: July 17, 2021, 07:46:25 am »
The Talos II wiki (https://wiki.raptorcs.com/wiki/POWER9_Hardware_Compatibility_List/Memory) makes the following claim:

"Ram will be running at a potentially slower frequency (2666, 2400, or 2133) based on if there is 1, 2 or 4 DIMMs per channel"

However, I have not been able to find any additional information elaborating on this.  I'm looking at building out a high-powered workstation, so I'm going to end up with all memory slots full; however, I'm not keen on paying extra for memory with a faster clock that I won't use (that, and at least in the old days, it would decrease performance if the memory and bus clocks weren't sync'ed).

Is there any information anywhere that further elaborates on what the memory clock frequencies are for the number of DIMMs per channel?

ClassicHasClass

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Re: RAM clock with full channels
« Reply #1 on: July 17, 2021, 07:05:11 pm »
Speed decreases with the number of DIMMs per channel. You get the full 2666MHz with a single DIMM per channel, 2400 for 2, 2133 for 4. However, the controller for each processor has 8 channels, and the T2 has 8 DIMM slots per CPU, so I don't think you're going to have a problem as long as you have both CPU sockets populated.

Here's what lshw reports on my 64GB dual-8 Talos II (the workstation I'm typing on):

Code: [Select]
     *-memory
          description: System memory
          physical id: 0
          size: 64GiB
        *-bank:0
             description: RDIMM DDR4 2666 MHz (0.4ns)
             product: 36ASF2G72PZ-2G6F1
             vendor: Micron Technology
             physical id: 0
             version: 0000,19 20,25
             serial: 0xf054945f
             slot: UOPWR.A100059-Node0-DIMM2
             size: 16GiB
             clock: 2666MHz (0.4ns)
             capabilities: ecc spd-1.1
             configuration: errordetection=ecc rank=2
        *-bank:1
             description: RDIMM DDR4 2666 MHz (0.4ns)
             product: 36ASF2G72PZ-2G6F1
             vendor: Micron Technology
             physical id: 1
             version: 0000,19 07,0F
             serial: 0x20ab81d0
             slot: UOPWR.A100059-Node0-DIMM6
             size: 16GiB
             clock: 2666MHz (0.4ns)
             capabilities: ecc spd-1.1
             configuration: errordetection=ecc rank=2
        *-bank:2
             description: RDIMM DDR4 2666 MHz (0.4ns)
             product: 36ASF2G72PZ-2G6F1
             vendor: Micron Technology
             physical id: 2
             version: 0000,19 20,25
             serial: 0xf054948a
             slot: UOPWR.A100059-Node0-DIMM10
             size: 16GiB
             clock: 2666MHz (0.4ns)
             capabilities: ecc spd-1.1
             configuration: errordetection=ecc rank=2
        *-bank:3
             description: RDIMM DDR4 2666 MHz (0.4ns)
             product: 36ASF2G72PZ-2G6F1
             vendor: Micron Technology
             physical id: 3
             version: 0000,19 07,0F
             serial: 0x20abb8b7
             slot: UOPWR.A100059-Node0-DIMM14
             size: 16GiB
             clock: 2666MHz (0.4ns)
             capabilities: ecc spd-1.1
             configuration: errordetection=ecc rank=2