Quad-channel, 2 pairs of 16GB combined with 2 pairs of 8GB.

[Selman Tabet]

Hi,

Is it possible to pair 4 sticks of 16GB (64GB) DDR4 to my currently installed 4 modules of 8GB DDR4 RAM? If this was to work, I'd end up with a total of 96GB of RAM. My motherboard has 8 RAM slots, ASUS X399 ZENITH EXTREME if that's needed.

Also, my 8GB modules are rated at 3866MHz while my motherboard currently supports 3200MHz stable so I had to underclock it (long story as to why my memory's speed is too much for the build). Still didn't figure the right CAS Latency for them.

Would getting those 16GB modules (if possible) at lower rated memory speeds than the 8GB modules, like 3200MHz, would be fine or should I just match the memory speeds across all modules?

Thanks in advance.

 

[thx1138v2]

AFAIK, the memory timings have to match exactly for them to work together at all.

If they work together, then from section 1.1.4 of the manual applies: "You may install varying memory sizes in Channel A, Channel B, Channel C, and Channel D. The system maps the total size of the lower-sized channel for the quad channel configuration. Any excess memory from the higher-sized channel is then mapped for single-channel operation."
http://dlcdnet.asus.com/pub/ASUS/mb/socketTR4/ROG_ZENITH_EXTREME/E13034_ROG_ZENITH_EXTREME_UM_WEB.pdf?_ga=2.233014749.230981665.1506766751-673777931.1506766751

So 32GB (4X8GB) and 32GB (2X16GB) would be quad channel and 2X16GB would be single channel. Each module has a 64Bit wide data path. Running modules in quad channel makes the data path appear to the processor as 4X64 (256 bits) so more data can be read/written at the same time. Single channel can only read/write 64 bits at a time.

But it will be dependent on the specific processor used also since that's where the memory controller resides.