Question using 5/6 out of 8 ram slots on sTRX4

Aug 10, 2021
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I am buying a sTRX4 motherboard for the 3960x threadripper. I need roughly 140 gb of ram for my tasks. What is the optimal way to set this up RAM wise? Must I use all 8 slots at 32gb for 258gb total? Or can I use 5 or 6 of the slots to save some money? I am assuming I also cant mix and max 32gb/16gb sticks without compromising performance as well.
 
2, 3, 4, 6 or 8 dimms populated is normal supported memory configuration
any other number of slots used may work or it may not work

quad channel (max bandwith) is either 4 or 8 sticks

you can mix 32 and 16gb modules, cpu has multiple memory controller, but mix them in pairs and try to stick with same brand/model/speed rating as not every mainboard can properly run mixed ram

144 gigs of ram would be like this:
a1+b1 slots 2x16GB
a2+b2 slots 2x32GB
c1+d1 slots 2x8GB
c2+d2 slots 2x16GB
 
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I am buying a sTRX4 motherboard for the 3960x threadripper. I need roughly 140 gb of ram for my tasks. What is the optimal way to set this up RAM wise? Must I use all 8 slots at 32gb for 258gb total? Or can I use 5 or 6 of the slots to save some money? I am assuming I also cant mix and max 32gb/16gb sticks without compromising performance as well.
This is kind of old so make your own call.
https://www.pcworld.com/article/423521/quad-channel-ram-vs-dual-channel-ram-the-shocking-truth-about-their-performance.html

Perhaps if you have enough cpu muscle the extra channels are a plus.
 
This is kind of old so make your own call.
https://www.pcworld.com/article/423521/quad-channel-ram-vs-dual-channel-ram-the-shocking-truth-about-their-performance.html

Perhaps if you have enough cpu muscle the extra channels are a plus.
that article is from 2015, CPUs got better since than, dual ddr4 2666 can run around 40GB bandwith...that article has 27gigs, which tells how poor that CPU is as it cant even utilise properly dual channel

anyway, having multiple modules means better ram latencies, as memory interleaving kicks in, so cpu waits less for commands as it can use unused banks in meantime
tho threadripper has kinda high ram latency (100+ns), can be tuned to around 70ns
youll see difference once all cpu cores will be doing memory intensive tasks, but not every cpu tasks needs high ram bandwith or latency, if program works with small data sets which fits in cpu cache, then ram gets somewhat ignored
 

kanewolf

Titan
Moderator
I am buying a sTRX4 motherboard for the 3960x threadripper. I need roughly 140 gb of ram for my tasks. What is the optimal way to set this up RAM wise? Must I use all 8 slots at 32gb for 258gb total? Or can I use 5 or 6 of the slots to save some money? I am assuming I also cant mix and max 32gb/16gb sticks without compromising performance as well.
If you "need" 140GB for your tasks, then you also need to leave RAM for the OS. It will want RAM for I/O caching and context switches.
Also if you need 140GB, then I would recommend ECC RAM. You can use non-ECC with Threadripper, but when your RAM exceeds 128GB total, I always recommend ECC.
I would probably do 4x32 + 4x16 -> 192GB. That way you have RAM for the OS and if you didn't estimate your RAM usage you have some room to adapt.
 
that article is from 2015, CPUs got better since than, dual ddr4 2666 can run around 40GB bandwith...that article has 27gigs, which tells how poor that CPU is as it cant even utilise properly dual channel

anyway, having multiple modules means better ram latencies, as memory interleaving kicks in, so cpu waits less for commands as it can use unused banks in meantime
tho threadripper has kinda high ram latency (100+ns), can be tuned to around 70ns
youll see difference once all cpu cores will be doing memory intensive tasks, but not every cpu tasks needs high ram bandwith or latency, if program works with small data sets which fits in cpu cache, then ram gets somewhat ignored
There are some newer articles that are showing the same thing.
But again it might depend on what cpu is on the other end of the pipe.
 

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