Steve, this is long, but worth the read.
Apparently, it's not the "4x8GB" that helps the Zen3. It's that using full "4-Ranks" (256-Bits of memory bandwitdh) will be optimal because of the memory cycles. It's something about allowing more cycle to start while more are finishing.
Ram sticks have ranks. Most if not all 8GB sticks are Single Rank. Which means if you remove the heat spreader, you will have all of the IC's on one side of the PCB. 1 stick of 8 chips on one side will requires 64-Bits of bandwidth. (single rank) Using 2 sticks of Single Ranked RAM sticks will use 128-Bits of memory bandwidth. When you use 4 sticks of SIngle Ranked RAM sticks, you'll fully utilize the 256-Bit bandwidth. More than that will overload/strain most CPU's memory controllers and you'll reach diminishing returns on CPU performance for trying to double your RAM. You may also limit your OC capabilities.
The "Sweet Spot" is 4 ranks of memory. This CAN BE HAD with 2 sticks of RAM, as long as both sticks are Dual-Ranked (meaning there are chips on both sides of the PCB). This is typically found in 16GB sticks. This is why people going for 32GB system memory may be in luck and reap these benefits with 2 sticks of 16GB Dual Ranked sticks. That will be a total of 4-Ranks (256-Bits).
Upon searching what kind of config would be best for a Zen3 system seeking 64gb of memory, I have stumbled upon the fact that the Crucial Ballistix MAX 16GB sticks are SINGLE RANKED. (Micron chips). Not only that, but they come in 4000mhz CL18 @ 1.35v. Which would be a GREAT candidate for people trying to reach the 2Ghz infinity fabric. The beauty of this ram is that you can buy 4 sticks of 16GB dimms, and be running only 4 Ranks and reap all the performance benefits while not overloading the CPU memory controller. This way you can achieve 64GB of ram for those that require it.
I was watching some reviews on this memory and left some useful feedback for some. I have pasted it below for people seeking this type of information: Regarding the Crucial Ballistix MAX 4000Mhz 32GB (2x16GB kit) If anyone is wondering why this ram is so expensive compared to other 32gb kits...
Each 16gb module is single ranked. Totaling 2 ranks. That means that the memory IC chips are all on one side. 8 chips. Each chip size is 2gb. Each rank requires 64-bits of bandwidth. These are Micron Chips. Micron is one of the only companies that does this in the performance market.
Samsung B-Die chips are limited to 1gb IC's which means if you were to get a 16gb module with Samsung B-Die or other competitors, they would have 8 chips on "each" side to equal the 16gb ram capacity, meaning they are dual ranked, using 128-bits per module.
AMD platforms do NOT like more than 4 ranks of memory (256-bits). So lets say you want 64gb of ram. Getting 4 of these sticks would equal 4 ranks of memory (256-bits), which in Daisy Chain memory topology, can actually perform better than just two sticks of single rank memory (using only 128-bits). If you wanted 64gb of ram in 4 ram slots and you went with Samsung B-Die IC's or non-Micron, you'd get 16gb modules with memory IC's on both sides of all 4 dimms which equals 8 ranks since each dimm is dual ranked (512-bits). This could overload your CPU's Memory Controller, limiting your OC to your CPU AND your Memory.
I suggest really doing research on finding the best ram for your AMD platform if that's what you have. Intel isn't AS sensitive to this, but it still is to a point.
There is a fine balance with AMD's Zen2 currently. It's somewhere around 16 cas latency and 3800Mhz Ram with a 1900Mhz infinity fabric. These 4000Mhz dimms are great because if Zen3 can overclock their infinity fabric to 2ghz, you can run a 1:1 with this ram. The advantage to this is: A higher infinity fabric will equal great performance boosts across the board on AMD (gaming, computing etc...). When you run 3200mhz ram, your infinity fabric is 1600mhz (same frequency as the ram before DDR). If you run 3600mhz Ram, your infinity fabric gets cut in half since it will not go to 1800mhz unless you force it and possibly adjust voltage for stability. So now you see why if Zen3 allows a 2000mhz infinity fabric, this 4000mhz ram would be quite the sweet spot as you could run a 1:1 divider.
Not to mention, when overclocking your ram & cpu on Ryzen... the SOC voltage has to be increased, and often times once that's pushed passed 1.1v, you can be victim of having your PCI-E 4.0 down-spec itself to PCI-E 3.0. This can affect users which are trying to benefit from the max GPU performance from newer graphics cards, and most importantly... any users using new generation PCI-E 4.0 NVME drives such as Corsair's or Gigabyte's current offerings. Hope this answers your question as to why this ram is expensive compared to other 32gb (2x16gb) kits. These sticks are single ranked and most if not all are dual ranked. Because of this, it allows you to not complicate all of the above mentioned since it can operate a 64GB setup with only 4-ranks @ 256bits that won't need a high SOC voltage, and allow a possible Infinity fabric overclock of 2GHz on the new Zen3 platform which means you can run a 1:1 divider between the memory and the fabric. (2000mhz D.D.R. "Double Data Rate" = 4000mhz ram).
Finding 4000mhz 16gb modules that are single ranked @ CL18 and 1.35v is not an easy task. Micron chips are charging for that novelty. I don't blame them for the price. Hope this helps someone in their searches for the right ram sticks for their Ryzen Zen3 & Zen2 systems.
Quelle:
https://www.youtube.com/channel/UCCV2V4NAGAeuD7V_TZ0v3jA
