Question Best Memory for 3900X? DDR4-3600?

Status
Not open for further replies.

ch33r

Distinguished
BANNED
Jun 13, 2010
316
4
18,685
0
Ok, but what about performance. I been reading that 3200 could bottleneck a 3900X. No? I don't think AMD is recommending 3600 just because of price/performance's and what 1 to 1 and 2 to 1 mode
 
They seem to recommend 3600 because those are the fastest sticks you can get without slowing down the Infinity Fabric and increasing latency between cores. Technically this doesn't happen until you go past 3733MHz on RAM, but nobody actually sells 3733MHz RAM sticks, so they recommend 3600 so people don't go out and buy 3800 sticks and then complain when their CPU runs slower than the benchmarks.
 
Reactions: SgtScream

ch33r

Distinguished
BANNED
Jun 13, 2010
316
4
18,685
0
They seem to recommend 3600 because those are the fastest sticks you can get without slowing down the Infinity Fabric and increasing latency between cores. Technically this doesn't happen until you go past 3733MHz on RAM, but nobody actually sells 3733MHz RAM sticks, so they recommend 3600 so people don't go out and buy 3800 sticks and then complain when their CPU runs slower than the benchmarks.
Why would faster memory slow down the CPU?
 
Why would faster memory slow down the CPU?
Apparently it's due to how they've designed the Infinity Fabric to work. With RAM speeds less than 3733 MHz, the Infinity Fabric runs at 50% of that RAM speed, but if you exceed 3733MHz on the RAM, then the Infinity Fabric only runs at 25% of the RAM's speed, effectively slowing it down unless you have some extremely high speed RAM eg. 5000 MHz or higher and can actually get it to run at that speed. Slower Infinity Fabric means more latency between the core clusters and that could slow the CPU down more than having faster RAM would help it.
 

jwcrellin

Reputable
Dec 3, 2016
1,274
19
5,665
152
You will notice the performance difference if you are going from ddr4 2400/2666 to 3600/3733MHz. If you already have a 3200 kit, stick with it, you will not notice any improvement by spending money on 3600.
 
So according to

https://www.techpowerup.com/review/amd-zen-2-memory-performance-scaling-benchmark/images/intro3.jpg

apparently DDR4-3600 is recommended for a 3900X, not DDR4-3200. But its rated for 3200. Thoughts?
I think that recommendation relates to two things: first, what happens when memory clock speed exceed something like 3733. At or above that the Infinity Fabric speed drops to a one-two ratio from a one-one ratio, or 1/2 the memory clock, so overall performance will drop even at higher memory speed.

Second: Zen3 eagerly overclocks memory so why not? Just not above 3600...
 

jwcrellin

Reputable
Dec 3, 2016
1,274
19
5,665
152
I think that recommendation relates to two things: first, what happens when memory clock speed exceed something like 3733. At or above that the Infinity Fabric speed drops to a one-two ratio from a one-one ratio, or 1/2 the memory clock, so overall performance will drop even at higher memory speed.

Second: Zen3 eagerly overclocks memory so why not? Just not above 3600...
Ryzen 3700x has been tested to run stable with memory up to 4900MHz. Truly that is blazing fast. But the cost of a ddr4 5000 kit is astronomical. At some point you start getting diminishing returns. AMD has some smart engineers working for them. If they say that 3600MHz is the price to performance sweet spot, i'd trust them.
 
Ryzen 3700x has been tested to run stable with memory up to 4900MHz. Truly that is blazing fast. But the cost of a ddr4 5000 kit is astronomical. At some point you start getting diminishing returns. AMD has some smart engineers working for them. If they say that 3600MHz is the price to performance sweet spot, i'd trust them.
That's what I'm counting on my 3600 RAM is working fine with my setup but gains over 3200 are minimal. With 3rd gen Ryzen, "natural" IMC frequency is 3200MHz (up from 2933 fro 2nd gen and 2666 for 1st gen), 3600 is still in 1:1 bracket but in this setup latency is 64.2.
 

ch33r

Distinguished
BANNED
Jun 13, 2010
316
4
18,685
0
Im looking to build a powerhouse PC based on the 3900X. I want 32GB of RAM, DDR4-3600, CL16. Whats the best configuration?

1 x 32GB
2 x 16GB
4 x 8GB

Will either of those configurations be slower or faster than another or be a "bottleneck"? Will any of those configurations cause the memory/CPU to perform at a lower spec?
 
On dual channel motherboards best config is kit of 2 modules.
In this case - 2 x 16GB.

1 x 32GB - single channel mode (lowered performance);
2 x 16GB - dual channel mode 1T command rate (optimal performance);
4 x 8GB - dual channel mode 2T command rate (slightly lowered performance).
 

NightHawkRMX

Illustrious
What will the performance loss be with 17 vs 16
Difference between C16 and C17 is small, and well within the margin of error.
Adding 4 sticks will cause the command rate to jump to 2, hence the ram will be marginally slower but much more noticeable than the c16 vs 17. 4 sticks is just not ideal for a mainstream platform supporting only 1 and 2 channel.
 

ch33r

Distinguished
BANNED
Jun 13, 2010
316
4
18,685
0
Differences between CL16 and CL17 are very slim. Detectable in benchmarks only.

Anyway - always go with 2 module kit on dual channel boards.
4 modules may even have trouble running at rated frequency.
Ok, heres the problem. Any 2x16GB @ 3600 I can find on newegg are CL19. Why is AMD recommending CL16 if 2x16GB CL16 is not even a thing? The lowest I can find for 2x16 is CL19. I cant find any 3600's 2x16 lower than 19. Im on newegg Canada not newegg US. The one you showed me was the American version. Im in Canada. I even used PCPartPicker which searches everywhere and there are literally 0 results
 
Status
Not open for further replies.

ASK THE COMMUNITY

TRENDING THREADS