Question Chasing extreme memory OC on AM5 boards - 2 vs 4 slots ?

[Quinn2_Santini3]

I'm looking for something with minimal memory latency and maximal bandwidth on Zen5 .

Even though usual sweet spot is around 6000-6400MHz at 1:1, Im lookking for possibility at running it at 8000-8400 MHz at gearing 2:1.

This is at the top of the current MEMC reach in Zen5, but should be doable.

I am looking at economy segment of MoBos that could reach this and have also solid VRM for moderate CPU OC for work 24/7 and wonder how much does having only 2 RAM sockets and shorter lines improve signal quality (as found on mini-ITX and rare uATX boards) on high end ?

I know that having only 2 RAM slots is NOT the same as using only 2 out of 4 on ATX board, but I wonder how much difference does it make.

Anyone with experience and willing to share ?

 

[QyInvoLing]

It depends.
Giga's b650i ultra is an ITX motherboard which only has 2 memory slots, but its memory oc ability is far less than expected.

 

[CountMike]

I'm looking for something with minimal memory latency and maximal bandwidth on Zen5 .

Even though usual sweet spot is around 6000-6400MHz at 1:1, Im lookking for possibility at running it at 8000-8400 MHz at gearing 2:1.

This is at the top of the current MEMC reach in Zen5, but should be doable.

I am looking at economy segment of MoBos that could reach this and have also solid VRM for moderate CPU OC for work 24/7 and wonder how much does having only 2 RAM sockets and shorter lines improve signal quality (as found on mini-ITX and rare uATX boards) on high end ?

I know that having only 2 RAM slots is NOT the same as using only 2 out of 4 on ATX board, but I wonder how much difference does it make.

Anyone with experience and willing to share ?

For extreme RAM overclocking (to chase records for instance) only one RAM stick in primary slot is used to have least load on IMC in the processor.
For OC to get best performance scores, 2 sticks are needed because of better performance in dual memory channel mode. That puts load on only one of 2 IMC memory controllers in the mainstream consumer CPU. Using more sticks sticks (even 3) puts more load on IMC so it needs higher voltage and may overheat it and lower throughput
Difference between 2 or4 memory slots. is minuscule and doesn't have any role in normal use. Half an inch of a trace is practically nothing. That's my, many, 30+ years OC experience.
As far as CPU OC is concerned, it much depends on CPU itself and VRM on particular MB but trend with latest generations of CPUs is to already have best possible safe frequency built in the microcode, just need to make appropriate settings in the BIOS to enable them in full. Even temperatures are allowed to raise to that effect. Classic, old time OC would not bring much or any benefits and is discouraged because it may bring instability and danger from overheating.
Ps. any ratio other than 1:1:1 may bring lower actual performance so chasing frequency records can be only reason to try such extreme frequencies.

 

[Quinn2_Santini3]

I don't think so. Difference is not just in line load. Presence/absence of module also affects signal propagation (= signal reflections) etc. It's not for nothing that one has to use specific slot pair with only 2 sticks.

It's well known that single-rank modules clock generally higher ( all other things being equal) than dual rank models, and that in 2DPC (two DIMMs per channel) single-rank modules perform far better than dual-rank ones.

WRT ratios, there is strictly speaking no 1:1:1 ratio. Golden knee for ZEn5 is at memclkl 3000 Mhz (=6000Mt/s DDR) , IF CLK 2000 MHz.
So at parity memclk is 150% of IF clk.

If one enables gearing 2:1, that only influences command issue rate ( not transfer rate), so with even-cycle latency ( say 30 cycles) nothing is lot on that end.
But at 4000 MHz memclk ( = 8000 Mt/s DDR) and 2000MHz IF clk, one gets nice round integer ratio 2:1 that is even nicer than previous 1.5:1 and there is no async time loss.
So one gets 33% more bandwidth with less latency. Win-win all around.

If one can stretch IF CLK to 2133 MHz ( prerequisite for 6400MHz at gearing 1:1), this means 8400MHz at OC.

But for that to work, I presume one would need fast single rank 24GiB sticks and MoBO with good signal integrity... 🙄