Question Realistic difference between 2 and 4 ram sticks on dual channel?

wehler53

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Hi all,

So i am building a Ryzen 3900x based computer at the moment, and was wondering about the ram limitations with 4 sticks in a dual channel? Like i get that its hard to say for sure, but with 4 x 3200Mhz ram what would i realistically be seeing roughly with 4 vs 2? And how often is there an issue with using two dual channel kits together?
 

kanewolf

Titan
Moderator
The bandwidth is the same with 2 DIMMs or 4 DIMMs. Four DIMMs is more difficult to get 3200Mhz clock speed and there are a lot fewer matched sets of four DIMMs to choose from. With a dual channel CPU you are always better off with two DIMMs. If you want 32GB then buy two bigger DIMMs.
 
2 things:

1) The memory controller has a harder time clocking high with dual rank configuration, but dual rank performs better than single rank at the same speed. Installing 4 single rank dims will effectively make it dual rank. Installing 4 dual rank dimms will likely have to run slower and may not run at all.

2) Your DIMM slots will either be wired as daisy chain, or T topology. If it's daisy chain, then the signalling is better with just 2 dimms and can clock them higher than T topology. If it's T topology, the signalling is balanced for 4 dimms, and will perform better with 4 dimms than a daisy chain, but won't clock quite as high.

You are going to be dual channel regardless of 2 or 4 dimms. The question is what motherboard, and how much capacity RAM you need. It's probably better to get two higher capacity single rank dimms to start out with, for better compatibility if you add more later. Good luck with figuring out which ones are single rank, since that's a "hidden" spec that DRAM manufacturers rarely advertise, but can be seen with software like AIDA64 or Thaiphoon Burner.
 

wehler53

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The mobo is the Asus crosshair VIII Hero, the ram is G.Skill F4-3200C16D-32GTRS 16x2

I know that buying two sets of ram isnt a wise decision, and 32GB is more than enough for any sane person, but given that ive hit high 20's at times in the past, and i was going all out on my build and wanted the astetics i ended up with two kits of the same memory (second lot went on sale so it fell into budget), obviously if the second kit doesnt play nicely, then i can reuse in a future build or just sell it, particularly given how well second hand ram sells. My past builds have been on the 2011 (and variants) socket and ive always had quad channel avaliable so i keeply blew past the fact that AM4 only supports dual channel.

So essentially is impossible to hit the advertised speed when using all 4 slots? And IF i ever did NEED 64GB would it be only be efficent to use 2x 32GB sticks? and practically throw away money..
 
The mobo is the Asus crosshair VIII Hero, the ram is G.Skill F4-3200C16D-32GTRS 16x2

I know that buying two sets of ram isnt a wise decision, and 32GB is more than enough for any sane person, but given that ive hit high 20's at times in the past, and i was going all out on my build and wanted the astetics i ended up with two kits of the same memory (second lot went on sale so it fell into budget), obviously if the second kit doesnt play nicely, then i can reuse in a future build or just sell it, particularly given how well second hand ram sells. My past builds have been on the 2011 (and variants) socket and ive always had quad channel avaliable so i keeply blew past the fact that AM4 only supports dual channel.

So essentially is impossible to hit the advertised speed when using all 4 slots? And IF i ever did NEED 64GB would it be only be efficent to use 2x 32GB sticks? and practically throw away money..
Oh that's a board with T topology wiring so the board itself will run 4 sticks just as well as 2. The CPU memory controller itself will be the only limiting factor but you may be able to help it with some extra SOC voltage and dimm voltage to boost the signal strength.
 

wehler53

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Oh that's a board with T topology wiring so the board itself will run 4 sticks just as well as 2. The CPU memory controller itself will be the only limiting factor but you may be able to help it with some extra SOC voltage and dimm voltage to boost the signal strength.
How do you find that out? i had a look at it and all i could find was people saying all x570 boards were daisy chained (Though the hero wasnt out when these posts were made).

To be honest all this ram stuff is awfully confusing, im assuming that as the ram is 16GB per stick that means itll be dual rank right? Ive heard that some of the highend CPUs often perform better when they have all 4 DIMMS filled with ram, even seen videos claiming rather large differences any truth in this?
 
How do you find that out? i had a look at it and all i could find was people saying all x570 boards were daisy chained (Though the hero wasnt out when these posts were made).

To be honest all this ram stuff is awfully confusing, im assuming that as the ram is 16GB per stick that means itll be dual rank right? Ive heard that some of the highend CPUs often perform better when they have all 4 DIMMS filled with ram, even seen videos claiming rather large differences any truth in this?
I just doubled checked and you are right. That board is wired in series...

https://docs.google.com/spreadsheets/d/1wmsTYK9Z3-jUX5LGRoFnsZYZiW1pfiDZnKCjaXyzd1o/edit#gid=2112472504

You should try anyway and see if you can get them to run. It might take some effort and some extra voltage though.
 

TJ Hooker

Glorious
Herald
To be honest all this ram stuff is awfully confusing, im assuming that as the ram is 16GB per stick that means itll be dual rank right? Ive heard that some of the highend CPUs often perform better when they have all 4 DIMMS filled with ram, even seen videos claiming rather large differences any truth in this?
Only time I've seen this to be the case is when each stick is single rank, so 4 DIMMs results in two ranks per channel. Given you already probably have two ranks per channel, I doubt you'd see any performance advantage, possibly even a slight performance hit.
 

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