4x16GB or 2x32GB When using all of the same modules

LRichardMelbourne on 11/08/2020 - 19:13
Last edited 11/08/2020 - 19:46

Background: I'm assembling a new computer - AMD 3900, MSI X570 Tomahawk mobo, Sabrent 1TB Rocket NVMe 4.0 Gen4 PCIe M.2 - and the video card from my current PC (as I don't play games and the computer is for dev and will run VMs, Docker, etc.) which is a GTX 650ti (current PC is about 7 years old and wasn't a high-end card back then anyway).

I'm after 64GB 3600MHz RAM which will fit under a Noctua NH-D15 (in dual-fan configuration) and haven't been able to find a decent answer to the following:

If I use all identical 4 x 16GB or 2 x 32GB modules (identical as in, same brand and model) will the 4 x 16GB work better than the 2 x 32GB? I read somewhere something about AMD working better with 2 x 32GB, but I don't know if that's correct or not. I do know that selecting a higher clock speed is proportionally better than lower latency - thanks rajeh for saying about this countless times :)

Would appreciate any and all comments, thanks.

[Edit: I'm not planning on overclocking this computer, so perhaps I could just run the Noctua DH-15 in single-fan mode and then RAM clearance won't be an issue? Also read on the Noctua website that you can mount the second fan a bit higher - case clearance should be fine as I generally buy reasonably large cases]

Computing

Comments

  • [Deactivated] on 11/08/2020 - 19:24
    +2

    Are you helping tesla launch a rocket

    • RichardMelbourne on 11/08/2020 - 19:26

      lol. I don't buy new computers very often so I want something which will run smoothly for ideally around 5 years. And not associated with SpaceX :)

      • [Deactivated] on 11/08/2020 - 19:40

        16gb more than enough 👍👍

        • RichardMelbourne on 11/08/2020 - 19:44
          +2

          Per Virtual Machine? :)

          • [Deactivated] on 11/08/2020 - 20:09

            @RichardMelbourne: Using just 8gb to run VMs here 👌

            • Clear on 11/08/2020 - 21:31

              @[Deactivated]: What do you run on your VMs?

              • [Deactivated] on 11/08/2020 - 21:47
                +1

                @Clear: Nothing crazy enough for that much ram

            • Frayin on 11/08/2020 - 21:54

              @[Deactivated]: That must be hell.

              32gb ram minimum for the VMs i run.

              I nest VMs within VMs using vsphere.

              • Clear on 11/08/2020 - 23:28

                @Frayin: Similar here though I'm currently using a HPE DL360p Gen8 with 128GB RAM for my Hyper-V. Overkill for most setups I would imagine.

  • Void on 11/08/2020 - 19:49
    +1

    2x32GB because 4 sticks is much more stressful on the motherboard and CPU. Though I wonder how VMs take to 4 sticks vs 2.

    • RichardMelbourne on 11/08/2020 - 19:54

      I wouldn't have thought the VMs would know about physical RAM at that level (perhaps Hypervisor or VirtualBox manager might, but I'd be quite surprised). I don't run them all the time - just on demand, depending on the project I'm working on.

      So I guess best to go with 2 x 32GB then, and either mount the second fan higher, or remove it altogether - if necessary.

      Now I just need to wait for some to come up on OzBargain and preferably not from NewEgg (and arrive bent)…

      • Void on 11/08/2020 - 19:55

        I was thinking more about it having more channels.

        • RichardMelbourne on 11/08/2020 - 19:58

          I think you've convinced me to go with 2 x 32GB modules anyway, as 4 seems to be more problematic from posts I've found. I don't really want to risk buying something that won't work, will work unreliably, or will take forever and a day to try configure to get to work reliably.

        • weightedcube on 12/08/2020 - 00:52

          Consumer Ryzen only has 2 memory channels, so having 4 vs 2 modules wouldn't grant you any extra performance. Threadripper on the other hand has 4 memory channels, in which case you would want at least 4 memory modules.

          • Void on 12/08/2020 - 09:19

            @weightedcube: I was thinking with 4x16GB you'd get 2 interleaves with 2 channels (I think they're interleaves?) so if you are writing the full capacity it's faster? IDK lol.

            • weightedcube on 12/08/2020 - 13:20
              +1

              @Void: What you're referring to is rank interleaving, which can indeed improve performance but is a separate topic from memory channels. A CPU can use multiple memory channels simultaneously to increase performance (e.g. Dual Channel) however each memory channel can only access a single memory rank at a time. Within each memory channel, when you're doing an operation to a rank there is a delay (memory latency) before you can start the next operation. If you have multiple ranks of memory in a channel you can use rank interleaving to increase performance slightly. This works by using the delay time during an operation on one rank to start an operation on another rank of memory.

              We can think of a rank as a group of memory chips on a module. Typically these days a 8GB module is single rank meaning it's made of one rank that has 8GB of memory chips. Then a 16GB module is dual rank being comprised of 2x 8GB ranks totalling 16GB. Finally a 32GB module will be dual rank as well except made with 2x 16GB ranks. In theory you can have a single rank 16GB module but I believe it's more cost efficient to make a dual rank 16GB module as a single rank module would require denser memory chips that are more expensive.

              So if you're running 4x16GB modules in a dual channel setup, you have 2x Dual Rank Modules per channel, so 4 ranks on each channel. In comparison if you're running 2x32GB modules in a dual channel setup, you have 1x Dual Rank Module per channel, so 2 ranks on each channel. I'm not actually sure what the performance difference is between 2 vs 4 ranks on a channel, I've only seen numbers for 1 vs 2 ranks, in which 2 ranks is faster all other variables being the same.

              An important thing to note about rank interleaving performance is the load on the memory controller. When we talk about more memory sticks being more load on a memory controller, what is actually causing the load is the additional memory ranks. So if you had 4x 8GB Single Rank Memory Modules vs 2x 16GB Dual Rank Memory modules this would actually be the same load on the memory controller. The problem with more load on a memory controller is that it makes it harder to run higher speed memory.

              So now we have this predicament, more ranks = more performance from rank interleaving but more ranks = more load on the memory controller, so you will struggle to run better memory frequencies/timings. So in reality it's a complicated topic about what is good or bad, typically I believe the better choice is less ranks with better frequency/timings.

    • da1nonly on 12/08/2020 - 09:46

      I'm actually currently running 4 x 32GB in one of my servers atm with no issues at all.

      vmware seems to like it…
      few virtual appliances, virtual NAS and window servers.and its been up for the past 3 months…

      • Void on 12/08/2020 - 09:56

        Is it on Ryzen?

        • da1nonly on 12/08/2020 - 10:01

          yeah mate….

          3900x, tomahawk b450, G.SKILL TridentZ RGB Series 128GB (4 x 32GB)

          • Void on 12/08/2020 - 10:09
            -1

            @da1nonly: 3200? I highly doubt 3600 would work on 4 sticks.

            • da1nonly on 12/08/2020 - 10:12

              @Void: nah 3600…

              its working for me :)

              • Void on 12/08/2020 - 10:35

                @da1nonly: Wow. Either you have a golden IMC or Ryzen 3000 is just THAT much better.

                • da1nonly on 12/08/2020 - 10:45

                  @Void: i think it is the latter…

                  I've had no issues at all with my current rig as well…

                  3950x, mortar max, 4 x 16GB 3200c16 lpx ram overclocked to 3733 16-17-16-32 CR/1T @ 1.45v

                  • Void on 12/08/2020 - 10:51

                    @da1nonly: WTF you got B-die from cheapy LPX? That's craaaazy.

                    • da1nonly on 12/08/2020 - 10:55

                      @Void: version 4.31 :)

                      • Void on 12/08/2020 - 11:07

                        @da1nonly: How much did it cost?

                        • da1nonly on 12/08/2020 - 11:17

                          @Void: got this about a year ago when RAM prices were still quite high….

                          2 x 32GB kit was around $240 per kit after cashback.

        • idjces on 12/08/2020 - 15:53

          Conversely my ryzen 3600 struggled with 4 sticks of ram, I had to underclock further to pass memtest. I'd love to see voltages and timings of those who were successful.

          da1nonly said 1.45v above, perhaps that's a big part of it. I stuck with corsair's 1.35v (which is already above ddr4's 1.2v)

  • RobBoss on 11/08/2020 - 20:09

    Here's an article benchmarking dual vs quad channel (bit old but still alright). There are also plently on YT as well. BTW, being a PC gamer, that GTX 650ti paired with what you have inflicted a bit of pain on me haha.

    https://techguided.com/single-channel-vs-dual-channel-vs-qua…

    • RichardMelbourne on 11/08/2020 - 20:16

      Apologies, I meant ah, I'll grab a 2080ti :)

      And thanks for that article link - I'll take a look.

  • da1nonly on 11/08/2020 - 22:00
    +1

    Corsair LPX will fit underneath the d15 easily..

    More importantly just make sure your case is wide enough for the d15

    • Void on 12/08/2020 - 09:19

      Just overclock value RAM :p

    • RichardMelbourne on 12/08/2020 - 10:18

      Yup, for sure. I'll likely get the case and fan from the same place (probably the mobo, too), so I'll get them to confirm it will fit - then any issues and at least I should be able to return the fan for something else (or maybe case and get something even bigger).

  • hero000 on 12/08/2020 - 15:00

    I use my PC mainly for photo editing and virtual lab. I got 8x8. Honestly speaking I've never passed 30GB memory use. I would say save your $$ 32 GB more than enough.

    Take advantage of Azure free $280 credit. It has been very helpful for me.

  • MrQ88 on 15/12/2020 - 00:08

    I'm running 4x8gb G.skill trident z neo 3600mhz CL16 on my system.

    3800x
    MSI X570 Tomahawk
    MSI 5700 XT Gaming X @1440p.

    Used mainly for gaming. I'm getting anywhere between 5-15fps more with 4x8GB vs 2x8GB stock.

    O/C my memory to 3800mhz with infinity fabric clock at 1900mhz.

    Division 2
    Insurgency sandstorm
    F1 2020
    GTA V

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