single stick of 32GB of S5/Z5?

[thetrystero]

anandtech (https://www.anandtech.com/show/17269...cturers-matter) found that dual rank ddr5 has a 9% performance advantage over single rank. they tested 2x32gb dual rank vs 4x16gb single rank. if i'd like to take advantage of dual rank but only need 32GB ram, can i use a single stick of 32GB? i vaguely recall that it's not advisable to use a single stick of ddr4 as it's very slow. does the same apply to ddr5 as well? in that case are any of the gskill 16gb sticks dual rank? i'm looking to use a 6400 cl 32 if possible on the asrock z690 taichi. thanks.

[emissary42]

The performance loss from not utilizing one of two memory channels heavily outweighs the difference between different module organizations*. So in general 2x16GB > 1x32GB, which is also the reason why dual channel kits are recommended and the de facto standard for both mainstream platforms.

[thetrystero]

so it turns out that my mobo (asrock z690 taichi) will not support 32GB at 6400. for 6400 it can only support up to 16GB. will a 4x16GB be significantly slower than a 2x32GB, assuming that my IMC can handle four slots without loss in frequency? also under the column "DIMM SOCKET SUPPORT" it says 2. does that mean i can only populate 2 dimms at not four?

https://www.asrock.com/MB/Intel/Z690...dex.asp#Memory

[emissary42]

assuming that my IMC can handle four slots without loss in frequency?

That is not the case. The highest frequencies are supported with only two modules in the primary DIMM slots. If you also populate the secondary slots, the maximum frequency will be lower, in some cases drastically.

also under the column "DIMM SOCKET SUPPORT" it says 2. does that mean i can only populate 2 dimms at not four?

It means that the specification in question is only supported with two modules, not four.

If you require more than 2x16GB or 2x24GB, you will have to compromise some memory frequency for the additional capacity of either 2x32GB, 2x48GB or 4x16GB (actual quad kits are fairly rare).

All officially compatible G.SKILL kits for the ASRock Z690 Taichi from the RAM configurator:

https://www.gskill.com/configurator?...del=1635745460

[thetrystero]

if i do purchase something that's not on the compatibility list, with the understanding that i'll not hit the max frequencies, will it still work at the base frequencies without xmp, or will it not work at all? i'm thinking of getting the F5-6400J3239G32GX2-RS5K which is not on the compatibility list, so i can use it in future when i upgrade my mobo. is this a bad idea?

[emissary42]

The default speed should work, since that is common ground for all DDR5 systems. The QVL specifically shows the proven compatibility of the XMP of that SKU.

In most cases you can still use the XMP with a reduced frequency, like for example DDR5-6000 with the ASRock Z690 Taichi. However that is something that was not tested and your results may vary. It really comes down to your specific components and their individual capabilities.

Usually buying memory for a hypothetical use case in the future is not a good idea, since preferences can change over time and with available options. If you make the switch to AMD for instance, you'd want an EXPO enabled kit instead.