Can somebody explain DIMMs, Frequencies and CAS Latency to me?

[RhysMusique]

Hey all, 

 

So I've preordered an RTX 3090 for my next build, which I'm looking to pair with the new 5900X or 5950X from AMD (I'll cast my judgement when I see the announcement). I've always wanted an all out gaming rig and I've saved up for so long, I can finally spend the money on it happily.

 

Questions I have are to do with the memory, however. Looking at some G.Skill Trident Z Neo modules, probably going to get 4 modules because I want to see the full bank on the motherboard. Weird but you know how it is.

So I'll either go with 4x8GB (the more affordable, probably-gonna-be-okay-with-32GB option) as opposed to 4x16GB.

 

-Is there any benefit of using 2 DIMMs of 16GB over 4 DIMMs of 8GB, when installing memory? Faster access etc? (Is it worth the tradeoff of not having a full bank and never being satisfied with how it looks?)

-I'm looking to get 3600MHz modules. but notice the latencies go up when you start to raise the frequency, unless you want to spend an unfathomable amount on RAM. I know we can't be sure how Zen 3 will react to memory speeds, but based on Zen 2, is it better to get something like a 3200MHz CL14 kit (14-14-14-34), or a 3600MHz CL16 kit (16-16-16-36)? Or does it really not make that much difference at all?

 

Sorry for the long winded post but I want this build to have as few 'what ifs' as possible!

 

Cheers, 

 

Rhys

 

 

[minibois]

4 minutes ago, RhysMusique said:

-Is there any benefit of using 2 DIMMs of 16GB over 4 DIMMs of 8GB, when installing memory? Faster access etc? (Is it worth the tradeoff of not having a full bank and never being satisfied with how it looks?)

It's easier on the memory controller of the CPU, meaning with two sticks there is a better chance of reaching the highest speed and lowest latencies.

4 minutes ago, RhysMusique said:

but based on Zen 2, is it better to get something like a 3200MHz CL14 kit (14-14-14-34), or a 3600MHz CL16 kit (16-16-16-36)?

Those are equal, if we're just looking at the speed and first latency number.

 

Personally I always recommend going with 2x whatever to get the right amount of GB for now (like 2x16GB in your case). That leaves room for expansion, but also means you can get the full speed out of your memory.

3200Mhz CL14 or 3600Mhz CL16 doesn't matter, pick whatever is cheaper basically (since the performance will be the same, based on how Zen 2 performs now.

[spartaman64]

cas latency / mhz = x then use x to compare different ram the lower the better

[gloop]

9 minutes ago, RhysMusique said:

Is there any benefit of using 2 DIMMs of 16GB over 4 DIMMs of 8GB, when installing memory? Faster access etc? (Is it worth the tradeoff of not having a full bank and never being satisfied with how it looks?)

Technically one is ever so slightly faster, but nothing you’d notice in real use. The only real difference is 2x16 allows for upgrading to 64GB in the future. 

 

9 minutes ago, RhysMusique said:

I'm looking to get 3600MHz modules. but notice the latencies go up when you start to raise the frequency, unless you want to spend an unfathomable amount on RAM. I know we can't be sure how Zen 3 will react to memory speeds, but based on Zen 2, is it better to get something like a 3200MHz CL14 kit (14-14-14-34), or a 3600MHz CL16 kit (16-16-16-36)? Or does it really not make that much difference at all?

The general rule of thumb is that going up 200MHz in speed is equal to 1 CL. 
 

Both of the ram kits you listed there are very good bins, however I’d personally go for the 3200 one as it is almost certainly BDie. It could also possibly reach 3600MHz C14 with a bump in voltage to 1.45v/1.5v. 

[Hairless Monkey Boy]

If you want a good overview of the primary timings including how they relate to clock cycles, this article from a while ago does a pretty good job.

 

https://www.gamersnexus.net/guides/3333-memory-timings-defined-cas-latency-trcd-trp-tras

[RhysMusique]

11 minutes ago, minibois said:

It's easier on the memory controller of the CPU, meaning with two sticks there is a better chance of reaching the highest speed and lowest latencies.

Those are equal, if we're just looking at the speed and first latency number.

 

Personally I always recommend going with 2x whatever to get the right amount of GB for now (like 2x16GB in your case). That leaves room for expansion, but also means you can get the full speed out of your memory.

3200Mhz CL14 or 3600Mhz CL16 doesn't matter, pick whatever is cheaper basically (since the performance will be the same, based on how Zen 2 performs now.

Thanks for your guidance! Not mnuch to choose between the two of them by the sounds of it, money takes over then! 

 

 

10 minutes ago, spartaman64 said:

cas latency / mhz = x then use x to compare different ram the lower the better

Handy tool! I'll keep that in mind, Thanks!

 

11 minutes ago, gloop said:

Technically one is ever so slightly faster, but nothing you’d notice in real use. The only real difference is 2x16 allows for upgrading to 64GB in the future. 

 

The general rule of thumb is that going up 200MHz in speed is equal to 1 CL. 
 

Both of the ram kits you listed there are very good bins, however I’d personally go for the 3200 one as it is almost certainly BDie. It could also possibly reach 3600MHz C14 with a bump in voltage to 1.45v/1.5v. 

Yeah they look like nice memory modules! I have Corsair Vengeance modules in my system in the moment, and when i tried to upgrade the 2x8GB kit with another identical revision number 2x8GB kit, motherboard hated it, that's why I'm not too much of a fan of leaving the gaps for the upgrade I guess, because I know i'll always have a bit of a worry about upgrading.

What is BDie if you don't mind me asking?

 

11 minutes ago, HairlessMonkeyBoy said:

If you want a good overview of the primary timings including how they relate to clock cycles, this article from a while ago does a pretty good job.

 

https://www.gamersnexus.net/guides/3333-memory-timings-defined-cas-latency-trcd-trp-tras

Thank you! I'll have a look at this in a little while!

[Hairless Monkey Boy]

2 minutes ago, RhysMusique said:

What is BDie if you don't mind me asking?

Not all DDR4 is created equal. Samsung's "B Die" as it's called is known to be some of the best performing DDR4, and tends to have tighter timings vs competing options.

[Moonzy]

32 minutes ago, RhysMusique said:

Is there any benefit of using 2 DIMMs of 16GB over 4 DIMMs of 8GB, when installing memory? Faster access etc? (Is it worth the tradeoff of not having a full bank and never being satisfied with how it looks?)

1) depends if the 16GB dimms are single or dual rank, generally you want lower rank so you can run higher freq, but at the same freq, higher rank is better. higher freq>higher rank, most of the time

2) depends on motherboard topology. some motherboard can run 2x16 faster than 4x8.

 

35 minutes ago, RhysMusique said:

-I'm looking to get 3600MHz modules.

why? we dont know what runs best with the new CPU yet

35 minutes ago, RhysMusique said:

but notice the latencies go up when you start to raise the frequency, unless you want to spend an unfathomable amount on RAM

CAS latency =/= memory latency

because it also factors in memory frequency

 

36 minutes ago, RhysMusique said:

is it better to get something like a 3200MHz CL14 kit (14-14-14-34), or a 3600MHz CL16 kit (16-16-16-36)? Or does it really not make that much difference at all?

they're about the same for most games

but the 3600 will be advantageous if your task requires high memory bandwidth