Comment by gryn 2 days ago
did they also make a compatible motherboard ? because I can't get mine to go past 4800Mhz when my RAM is rated for 6400Mhz with AM5 CPU.
for those who hadn't done this for a while, PSA: motherboards these days have a RAM compatibility list on their product page, check it before overspending on RAM.
> PSA: motherboards these days have a RAM compatibility list on their product page, check it before overspending on RAM.
That's a valuable PSA, but FYI it's been that way since the 80s. I've been bitten by compatibility issues at least once a decade since the 90s myself, and the answer from forums or support is always "did you check the compatibility table tho?".
Some memory manufacturers have lists of motherboards compatible with a given memory kit. E.g. I checked that my motherboard was listed in [1] before buying the memory, and everything worked effortlessly together with EXPO on.
[1] https://www.gskill.com/qvl/165/393/1665020366/F5-6000J3040G3...
I had similar issue with my 3950x I had stability issues with 3600MT, so I optimized clicks instead (I loaded XMP profile and then changed clock to lower value before tightening clocks with memtest runs in between) What people often don't realize that dimm quality allows you to get lower absolute time before data is available for system. So when you lower clocks, you don't need to wait that many cycles for the data. In that case you might not get that much bandwidth that you would have originally, but you can get the same or similar latency also changing order of dimms on board can somehow alter how low you can get (I have 4 dimms and swapping 2 on the same channel improved significantly clocks that I was able to achieve - no idea why)
More than the specific list of which RAM is compatible check the table of how many slots/GB is supported at which speed. 1x 8 GB DIMM is a lot easier to drive than 4x 48 for example. Also keep in mind a lot of it depends more on the CPU than the motherboard itself, though both play a part, and the QVL should be a "safe bet". Particularly if you're willing to throw a bit of extra voltage at the RAM.
CUDIMs should help a bit with those scaling tables due to having the clock redrivers, but we'll have to see to be certain how much.
> 1x 8 GB DIMM is a lot easier to drive than 4x 48 for example.
That's a bit of an exaggeration. What matters are DIMMs per channel, and ranks per DIMM. Consumer systems have at most two memory slots per channel, so 2x 8GB modules installed correctly is just two separate instances of one DIMM per channel, and 4x48GB is two separate instances of two DIMMs per channel, with each module being dual-rank.
The best configurations for overclocking are supposed to be motherboards with only one memory slot per channel, so that when operating with one DIMM per channel there are no empty slots providing stubs of wiring that degrade signal integrity. But very few motherboards restrict themselves like this for the sake of memory overclocking.
4x 8 GB is still a lot easier to drive at high speed than 4x 48 GB, but yes, one factor in the above comparison is indeed the number of DIMMs per channel. Ranks per DIMM is definitely a factor as well, though on large capacity DIMMs that tends to be a one sided story. Another factor in the rabbit hole is banks, tying it all back.
The other part of 2 DIMM boards is the trace lengths can be that much shorter (they need to be the same length so fewer slots means less max length to match to).
> But very few motherboards restrict themselves like this for the sake of memory overclocking.
Though I'd hope they'd finally start doing it considering the per DIMM capacities DDR5 brings (32 GB, with 64 GB planned), and most consumers really not going for capacities that'd require 2 DPC (DIMM per channel).
1 DPC should've been the default by now with the amount of 1 DPC and 2 DPC boards swapped, as it's just making things worse in the most common use case
A lot of consumers care more about either of total capacity or the concept of "I can just double my cheap RAM later" than care about ~10% differences in RAM clock speed. The latter is for those that really know what they're doing to eek out a couple more percentage points in benchmarks or non-consumer use cases, the former appeal to both budget users and prosumers alike (just not OC enthusiasts).
From that angle I don't necessarily disagree with 4 channel boards being more common than 2 channel boards, even though I personally lean more towards a 2 channel board myself (well, depending how well CUDIMMS scale I may change my opinion).
And they’re often not stable even with the given XMP profiles. All of my XMP profiles throw errors and require backing off speed by a few hundred hertz to be stable.
Worth though. Much cheaper way to get a few extra percentage points than custom liquid cooling. And since every game where you would care about max FPS is bound by single threaded performance fast RAM is it.
I haven't done this for a while, but every time I come back around the new specs with even basic hardware blow the doors off my old rig.
The motherboard QVLs aren't particularly useful, the higher tier kits can often just not work as they're currently more often than not limited by the CPU memory controller quality instead of purely motherboard or RAM ICs.
Did you try 6200/6000 for the kit? 6400 is up there for speeds that may not work on AM5 with synced controller and memory clocks without tuning it yourself, or working at all. Or is that 4 DIMMs