Steve, this is long, but worth the read. Especially for the viewers seeking more depth. Apparently, it's not the "4x8GB" that helps the Zen3, or "2x16GB" being the sweet spot. It's that using "4-Ranks" rather than 2 is more optimal because of the memory cycles. It's something about allowing more cycle to start while more are finishing. The "Sweet Spot" is 4 ranks of memory. Not 16GB of memory. (Even in some cases, some boards get a performance boost with 8 Ranks, but 8 Ranks have downsides). 4 Ranks CAN BE HAD with 2 sticks of RAM, as long as both sticks are Dual-Ranked. Regardless of using 2x16GB or 2x8GB, if they are Single Ranked modules, you are losing out on performance regardless of your timings and memory frequency. Using 2x16GB "Dual Ranked modules" total 4 ranks, will yield the performance increase. 2x8GB "Dual Ranked modules" aren't likely to exist in DDR4 any longer. Most 8GB DDR4 modules are Single Ranked. Which is why 4 of them would give performance boosts because they add up to the 4 ranks, but if they existed, you'd also yield the performance increase since it would total 4 ranks. Ram sticks have ranks. Most if not all DDR4 8GB sticks are Single Rank. Which means if you remove the heat spreader, you will "likely" have all of the IC's on one side of the PCB. (Side note: Not ALL Dual Rank modules are double-sided. Not ALL Single Rank modules are single sided. It's more to do with architecture. But otherwise, true 90%+ of the time and I'm trying to keep this short). 1 stick of 8 chips on one side is typically Single Rank. Using 2 sticks of Single Ranked RAM sticks have a total of 2 Ranks. More than 4 ranks can reduce your ability to OC your ram, run 1T Command rate, and some report even less OC on the CPU (maybe because of loading up the CPU's memory controller. Dual Rank modules are "typically" found in 16GB DDR4 sticks or more (Quad Rank exist, but are more for Server application). 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. Just remember, dual ranked modules have more difficulty overclocking their frequency as well as running at a 1T command rate. So are 4 Single Ranked sticks the same as 2 Dual Ranked sticks? Yes and No. Yes: You will get roughly the same performance benefits since you are using 4 ranks. No: Dual ranked sticks are harder to overclock. Which is why very high clocked ram that come in large capacity "tend" to be single ranked. How do you find out if your ram is single or dual ranked? CPU-Z is an easy-quick one to download and run. Go to the SPD tab. If you're trying to find out what rank the modules are that you're looking to purchase, I suggest googling the part number and "review" and look to see if anyone posted screen shots of CPU-Z's SPD tab. 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). Meaning that 4x16GB modules would equal 4 ranks. 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 once AMD does work with AGESA and their BIOS to help obtain a likely stable 2Ghz infinity fabric. The beauty of large capacity modules being single ranked is that you can buy 4 sticks of them (16GB modules), and be running only 4 Ranks and reap all the performance benefits while not overloading the CPU memory controller, while having 64gb of total system memory. So lets say you want 64GB of RAM. Getting 4 of these sticks would equal 4 ranks of memory, which in Daisy Chain memory topology, can actually perform better than just two sticks of single rank memory. (Side note: 90%+ of consumer boards are Daisy Chain. T-Topology is quite rare. Some manufacturers will have T-Topology for reviewers 'pre-release', but when released, they go Daisy Chain. Please look into the board you purchase and memory architecture to further understand the topologies as this could be a very complicated topic to discuss). These are the reasons why Ballistix Max is priced at what it's priced. Each 16GB module is single ranked. The memory chips are all on one side. 8 chips. Each chip size is 2GB. 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 most other competitors, they would have 8 chips on "each" side to equal the 16GB ram capacity, meaning they are Dual Sided, and likely Dual Ranked. If you wanted 64GB of RAM in 4 ram slots and you went with Samsung B-Die IC's or non-Micron, you'd likely get 4x16GB modules that are Dual Ranked modules totaling 8 ranks. This could limit your OC to your CPU AND your Memory. How do I find out what chips my ram has? Download Thaiphoon. Check out some YouTube videos on how to use it. It's a useful tool. I removed all the "bits" about "bits" as it seemed to confuse people, and this also simplifies the post. (Also, it isn't really relevant to 4 Ranks giving more performance than 2). For those that commented on the "bits" about "bits" and are interested in the structures that I was talking about please read:
https://en.wikipedia.org/wiki/Memory_geometry There is a fine balance with AMD's Zen2 currently. It's somewhere around 16 CL (CAS Latency) and 3800Mhz Ram with a 1900Mhz infinity fabric. 4000Mhz modules are great because if Zen3 can overclock their infinity fabric to 2Ghz, you can run a 1:1 divider 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. Not to mention, when overclocking your RAM & CPU on Ryzen... the SOC voltage may have 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. 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. If you're in the market for either 3200Mhz or 3600Mhz ram for AMD, and you're a "set it and forget it" kind of guy, just get the 3600Mhz ram with the lowest CL you can afford. Turn on XMP, make sure your infinity fabric is running at 1800Mhz and you'll reap a lot of benefits. Especially if your 2 sticks are Dual Ranked. If they aren't, and your budget allows it... consider buying 4 sticks of Single Ranked, or two sticks of Dual Ranked for even more performance over the higher infinity fabric gains. Interesting read:
https://www.reddit.com/r/Amd/comments/gkqujk/my_experience_overclocking_4x16gb_64gb_dualrank/ For those that don't mind a long video by buildzoid:
