DDR5 8600Mhz issue

[TheNaitsyrk]

Hello there,

 

Recently OCed my RAM to 8400Mhz CL38 49 49 49 84 T2 1.48V and performance is great passed memtest multiple times with no errors 6 hours each time.

 

I also did 8600Mhz CL38 50 50 50 84 T2 1.48V and it also passed memtest multiple times.

 

I know DDR5 has little effect in Cinebench but it certainly does help a little.

 

When I set RAM to 8600Mhz my CB score with 6.0Ghz P core and 4.8Ghz E core OC is around 43800. However, with 8400Mhz it's 44800.

 

Can someone explain why that is? I would've expected the higher speed to help out a bit not degrade the performance.

 

Also booting and testing 8800Mhz but 11 errors in memtest so tweaking still in progress.

[Eigenvektor]

Because there are limits to how fast the CPU's memory controller can run. If you go beyond a certain speed, it'll drop to half the memory speed (Gear 2). You typically don't want to overclock beyond the point where speed is 1:1 (or 1:2 in the case of DDR5)

 

DDR5 operates in Gear 2 by default, so you might be dropping to Gear 4, i.e. 1:4 in terms of frequency (https://www.overclockers.com/ddr5-overclocking-guide/#Step_1_Frequency)

[TheNaitsyrk]

8 minutes ago, Eigenvektor said:

Because there are limits to how fast the CPU's memory controller can run. If you go beyond a certain speed, it'll drop to half the memory speed (Gear 2). You typically don't want to overclock beyond the point where speed is 1:1 (or 1:2 in the case of DDR5)

 

DDR5 operates in Gear 2 by default, so you might be dropping to Gear 4, i.e. 1:4 in terms of frequency (https://www.overclockers.com/ddr5-overclocking-guide/#Step_1_Frequency)

I'll renew my Aida64 subscription and double test this thanks a lot!

[TheNaitsyrk]

21 minutes ago, Eigenvektor said:

Because there are limits to how fast the CPU's memory controller can run. If you go beyond a certain speed, it'll drop to half the memory speed (Gear 2). You typically don't want to overclock beyond the point where speed is 1:1 (or 1:2 in the case of DDR5)

 

DDR5 operates in Gear 2 by default, so you might be dropping to Gear 4, i.e. 1:4 in terms of frequency (https://www.overclockers.com/ddr5-overclocking-guide/#Step_1_Frequency)

Does that look off?

[Eigenvektor]

4 hours ago, TheNaitsyrk said:

Does that look off?

Seems to be running in Gear 2 in both cases, i.e. looks fine to me. Memory controller frequency is half that of DRAM frequency. And DRAM frequency is as expected for 8600 MT/s and 8800 MT/s respectively.

 

How often did you run the benchmarks? The difference between 44,800 and 43,800 is only 2%, so roughly margin of error. Could simply be that memory bandwidth is not the limiting factor, so further increasing memory speed has no effect either way.