Question about underclocking RAM for latency

_Froyo · June 8, 2022

I'm going to upgrade to a Ryzen 5600X soon, and I'm looking for some better RAM to go along with it for a decent price. I've found this kit from TeamGroup rated at 4000 MHz C16 here: https://www.amazon.com/dp/B08R6552VS/?coliid=I2HSS4YY0VDIU8&colid=1HPW5U5XP9LYN&psc=1&ref_=lv_ov_lig_dp_it

I'd like to try to underclock this kit to 3600 MHz C14, since the kits that come at that spec by default are usually $15-$20 more expensive. Does anyone have any experience / success with accomplishing this on this kit? My motherboard is an MSI B550M Bazooka if that helps.

Also, if anyone knows whether the difference between 4000 MHz C16 and 3600 MHz C14 is too small to care about on Ryzen 5000, please do let me know.

Zando_ · June 8, 2022

39 minutes ago, _Froyo said:

Also, if anyone knows whether the difference between 4000 MHz C16 and 3600 MHz C14 is too small to care about on Ryzen 5000, please do let me know.

It's a big difference AFAIK, 4000Mhz will be markedly worse if your FCLK can't run 2000Mhz (which seems to be a chip-by-chip luck thing, not a guarantee). You want FCLK the same as RAM speed (so for 4000MT/s RAM that's 2000Mhz, for 3600MT/s that's 1800MHz), you need a marked clock lead to overcome the performance loss from decoupling FCLK and RAM speed.

I'd honestly just get a 3600Mhz C14 kit if the price difference is only $20. Worth it to know the RAM will work at the desired speed IMO.

RONOTHAN## · June 8, 2022

That is a kit of B die memory, and not a terrible price for B die (I've seen better but 4000C16 is a very solid bin for $85 new). I haven't used that exact kit but I've overclocked a lot of different B die. So there's a couple things that you need to know

Changing the frequency and timings for better performance on RAM is still technically called overclocking. This is a nitpick, but just saying.
On Ryzen, you want to max out the Infinity Fabric (FCLK). On 95% of Ryzen 5000 series CPUs, the max stable Infinity fabric is 1900MHz FCLK. For the best latency, you want to have the memory and Infinity Fabric running in 1:1 mode, so if the FCLK is at 1900MHz, the DRAM frequency needs to be at 1900MHz (or 3800MT/s since RAM is double data rate). The single CCD chips like the 5600X do occasionally do a bit higher than 1900MHz, but it's still not a high likelihood, so your real aim should be for 3800MT/s.
CAS Latency is a function of frequency, so the calculated latency at 4000CL16 and 3600CL14 is basically identical (technically the 3600C14 config is faster). That said, the latency that matters for performance is the latency between the cores and the RAM, so running the infinity fabric higher means that you get lower latency, thus 3800MT/s CL16 is actually the same or better than 3600 CL14, even though the calculated latency is better on the 3600 CL14 config.
There's two ways you can go about doing this overclock, either enabling XMP and lowering the frequency down to 3800MHz (still an effective strategy and definitely quicker), or manually tune everything. Manually tuning everything can get you an extra ~5% performance if you do it right, since the sub-timings really do affect how a memory kit will perform.
- If you want to tune manually, aim for primary timings like 3800MT/s 14-14-14-21, settle for something like 3800MT/s 16-16-16-24. 1.5V DRAM is completely safe for B die, and given how those heat spreaders actually look like they do something, you might be able to go for something closer to 1.6V if you give it a fan (B die is very temperature sensitive, so the reason why most people say don't go over 1.5V for daily use is the performance differences are usually pretty small going above that and since the memory will be running hotter, you might actually be getting worse performance at those higher voltages). Sub-timings are important too, but for the most part you'll run the lowest you can for each of the different registers, making sure to save profiles regularly in case the system stops wanting to boot and you need to clear CMOS.
- Set the SOC voltage (what the memory controller runs on) to 1.15V, most of the Ryzen 3000/5000 series chips sweet spot somewhere between 1.1V and 1.2V, so so 1.15V is a pretty safe bet for what will work fine. I wouldn't run it above 1.2V for daily though, but it's completely safe running 1.15V daily.
- IIRC the B550M Bazooka isn't an exceptionally good motherboard for memory overclocking, but it's definitely not bad, and you should be able to run 3800MHz at decent timings no problem.

_Froyo · June 9, 2022

5 hours ago, RONOTHAN## said:

That is a kit of B die memory, and not a terrible price for B die (I've seen better but 4000C16 is a very solid bin for $85 new). I haven't used that exact kit but I've overclocked a lot of different B die. So there's a couple things that you need to know

Changing the frequency and timings for better performance on RAM is still technically called overclocking. This is a nitpick, but just saying.

On Ryzen, you want to max out the Infinity Fabric (FCLK). On 95% of Ryzen 5000 series CPUs, the max stable Infinity fabric is 1900MHz FCLK. For the best latency, you want to have the memory and Infinity Fabric running in 1:1 mode, so if the FCLK is at 1900MHz, the DRAM frequency needs to be at 1900MHz (or 3800MT/s since RAM is double data rate). The single CCD chips like the 5600X do occasionally do a bit higher than 1900MHz, but it's still not a high likelihood, so your real aim should be for 3800MT/s.

CAS Latency is a function of frequency, so the calculated latency at 4000CL16 and 3600CL14 is basically identical (technically the 3600C14 config is faster). That said, the latency that matters for performance is the latency between the cores and the RAM, so running the infinity fabric higher means that you get lower latency, thus 3800MT/s CL16 is actually the same or better than 3600 CL14, even though the calculated latency is better on the 3600 CL14 config.

There's two ways you can go about doing this overclock, either enabling XMP and lowering the frequency down to 3800MHz (still an effective strategy and definitely quicker), or manually tune everything. Manually tuning everything can get you an extra ~5% performance if you do it right, since the sub-timings really do affect how a memory kit will perform.

If you want to tune manually, aim for primary timings like 3800MT/s 14-14-14-21, settle for something like 3800MT/s 16-16-16-24. 1.5V DRAM is completely safe for B die, and given how those heat spreaders actually look like they do something, you might be able to go for something closer to 1.6V if you give it a fan (B die is very temperature sensitive, so the reason why most people say don't go over 1.5V for daily use is the performance differences are usually pretty small going above that and since the memory will be running hotter, you might actually be getting worse performance at those higher voltages). Sub-timings are important too, but for the most part you'll run the lowest you can for each of the different registers, making sure to save profiles regularly in case the system stops wanting to boot and you need to clear CMOS.

Set the SOC voltage (what the memory controller runs on) to 1.15V, most of the Ryzen 3000/5000 series chips sweet spot somewhere between 1.1V and 1.2V, so so 1.15V is a pretty safe bet for what will work fine. I wouldn't run it above 1.2V for daily though, but it's completely safe running 1.15V daily.

IIRC the B550M Bazooka isn't an exceptionally good motherboard for memory overclocking, but it's definitely not bad, and you should be able to run 3800MHz at decent timings no problem.