DDR5 overclocking (nightmare)


While CPU and GPU overclocking is relatively straightforward DDR5 overcloking can be an utter nightmare.

As you increase the DRAM frequency you will become increasingly likely to run into some stability issue. These stability issues can be very difficult to find in stability testing so you might think you have gotten your overclock stable only to then later down the line find some stability issue after doing further changes.

Stability issues can be due to the ram dies themselves becoming unstable but it can also be due to the memory controller that is integrated on the CPU or bad signal integrity between the CPU and the RAM. The imc will become a much bigger problem if you run more than 32 GiB of DDR5.

Since the memory controller sits on the CPU heat from the CPU cores can interfer with the imc making it less stable.


1. Maximizing the DRAM frequency
Your first priority is increasing the DRAM frequency as high as you can without it becoming unstable.

Increasing the DRAM frequency will also reduce the latency if you keep using the settings that came with the XMP profile. Eventually however some of these timings will become too tight as you push up the frequency higher. The issue then is that you do not actually know which timings (if any) that needs to be loosened if you nbaoticed instability so you might end up having to loosen up all in order to later tighten them up again until you find the culprits.

As you increase the frequency the minimum stable voltages will increase. Unfortunatily more voltage also mean more heat which itself can cause stability issues. Too high voltage can also be outright dangerous for components and this remains the case even if your temperatures are all safe. Higher voltage can also result in more signal distortion, especially on cheap motherboards.

I found the following voltages to be enough for stability at 6436 MT/s and 64 GiB of ram (dual rank) on the cheapest msi z790 motherboard.

CPU VDDQ: 1.26
CPU SA: 1.2
CPU VDD2: 1.4
DRAM voltage: 1.4
DRAM VDDQ voltage: 1.4

Since the g.skill ram has a terrible heat-spreader i ended up using a fan to keep the ram cool. Unfortunate with raptor lake it's hard to max out that memory in terms of frequency due to the sub-par imc, you end up having to run the memory in "gear2" which is slower than gear1 to get it stable and even then even reaching 6400 MT/s stable will be a challenge when you use more than 32 GiB. In addition the motherboard might also limit my overclocking headroom. Just getting it fully stable at 6400 difficult likely due me not having a proper CPU cooler contributing to higher IMC temperatures.

With single rank ram you will start running into imc issues at around 7200 and of course it becomes progressively harder to get it fully stable past that (at least in gear 2).


2. Stability testing
There isn't any single program you can rely on for reliable stability testing, instead you end up having to use multiple programs to verify that your ram overclock is indeed stable.


There are a lot of different ways in which you can use y-cruncher. The VST test might be the most useful when it comes to stressing the memory controller but that test alone will not detect all errors. By default each sub-test will run for just 2 minutes which might not be enough to verify that there isn't any instability due to continues stressing in the same way. It seems like changing the time each test runs to 600 seconds make it harder for unstable overclocks to pass.

Prime95 using the "largest FFT" or "blend" setting.

Linpack Extreme


I am not sure if stressapptest can be installed to windows but you can run it on linux via the following command (once you have installed it).
stressapptest -s 36000 -M 32768 -m 32 -W
Unfortunately that alone is not enough to find all potential instabilities despite taking 10 hours. One issue is that it relies solely on copy operations and might then miss stability issue if your read and write performance doesn't match (bottlenecking the stresstest) it also doesn't seem to stress the memory controller as hard as some y-cruncher tests. Still it's very good at catching errors and a good option if you use linux, it can sometimes quickly find instability that y-crunches missed despite running for hours.

These tests are good at booth loading the CPU and RAM at the same time which is particularly useful when you are imc limited.

Testmen5 will not stress the CPU much which is bad if you want to test if the imc is stable at the frequency it's running at under max cpu heat generation.



Tweaking timings
There are a lot of different timings you can configure. These can have a massive impact on performance but if just one of them is too tight you end up with an unstable system.

It's recommended that you do save a bios profile each time you change your timings. If you then find a stability issue you just go back one step at a time until the stability issue disappears. The reason for this is that properly stability-testing DDR5 is very arduous, especially when you have more than 32 GiB. It's probably faster not to properly test for instabilities and just move on since you discover it later down the line eventually anyway,.

I for example noticed stability issue in y-cruncher VST after i tightened tRDRDSG from 18 to 16, when i then reverted back to 18 the stability issue remained so i had to go back another step to the rRAS which i had set at 44, changing rRAS to 48 made it a lot more stable (no error so far even after tightening tRDRDSG again back to 16).

Higher tREFI is actually better in terms of speed (unlike all other timings where lower is faster or same speed).


Tertiary timings are very important
Having any of these be too high can have a massive impact on performance.

tRDRDSG and tWRWRSG shouldn't be higher than 8

sg = same group
dg = different group
dd = different die (same channel, different die)
dr = different rank

The dd timing will only be used if you have 4 ram dimms.
The dr timing will only be used if you have dual rank memory (such as 2x32 GiB).


The importance of a good motherboard
Some motherboard will be able to clock the ram much higher than others. The exact mechanisms for this is a bit unclear.

X61 reported that replacing msi pro z790-p with asus maxiumux z790 apex allowed ram overclocking to 7200 MT/s istead of struggeling to reach stability at 6600 MT/s with 2x32 GiB (dual rank) DDR5 (A-die).

A sign that your motherboard is bad is that you get your ram stable with low CPU VDDQ and CPU SA voltage but then cannot go higher even if you raise these.

One thing you can test is changing which slots you install the ram in. If it's a good motherboard changing to the other 2 slots shouldn't negatively affect how high you can overclock but some motherboard vendors cheap out on 2 of the slots making them worse than useless.

The old asus prime z690-A is limited to just 6200 in single rank operation.

You might think that the msi z690 unify-x would be good since it has just 2 ram slots but it actually isn't that great
M-die Power!!!! This is how tight I could get this kit, very impressed. I literally maxed out the trefi! 7800 was a no go. tried up to 1.7v, no dice. This is getting the same latency as my Gskill A-die at 8200 C36. I think I am returning both my A-die kits and keeping my M-die for a little longer.

Z790 Apex is a BEAST of a board... on my Z690 Unify-x with the EXACT same processor, The best I could get stable on this kit was 7000 C34, now I am doing 7600 C32, lol. Btw, for anyone that is wondering, my MC SP is between 80-82 whenever I check it.


What to look for when buying DDR5
With raptor lake you want to stick to 2 ram sticks. If you want 64 GiB you should buy 2 sticks of 32 GiB each rather than 4 sticks with 16 GiB each.

2x32 will be dual rank which is much harder on the memory controller but it also performs better than single rank at the same frequency. It's actually not clear what the best option is in terms of getting the best performance besides the fact that you get twice the capacity when going with 64 GiB which itself is very useful.

It's also not clear that hynix A-die would be better than hynix M-die. It seems like A-die is worse in terms of timings which is a significant disadvantage and often you cannot even take advantage of the higher frequency potential offered by A-die due to motherboard/IMC limitations.

Samsung memory tends to have the first 3 primary timings be the same such as 6000CL36, 36, 36

A-die and M-die tends to have lower cas latency while the tRCD is significantly higher such as 6000CL32, 38, 38, 38 and 6000CL30, 40, 40, 40

Samsung DDR5 does seem pretty good in terms of latency but it overclocks worse than M-die.

So given that there isn't any clear advantage for any type of memory you might just grab the cheapest 6000+ MT/s kit you can find since it's probably going to be good regardless besides the difference in cooling and the minor differences in terms of silicon quality. Samsung memory might be a better match for zen4 than raptor lake though (you probably want A or M die for raptor lake if your motherboard is good).


BLCK overclocking
The BLCK will not only affect the ram clock. It will also make your CPU faster and more efficient due to less voltage being applied relative to the frequency (unless you use static overclock where the voltage is fixed). This is a very good thing to do if possible.

You can find out the max stable BLCK frequency for the CPU simply by lowering the DRAM multiplyer to a lower value to make sure any error you see is from the CPU and not due to you pushing the ram/imc too hard.

Strange finding: BLCK does seem to give a greater performance boost than the actual increase of the relative increase of the BLCK clock (+2% from 0.8% increase of BLCK) but this are just early results that may not hold up.

6436 oc 7 stable.PNG

BLCK overclocking is very useful if you want to have a very stable overclock. You can simply tune it for maybe 102 BLCK and then when it seems to be fully stable make a second bios profile with the BLCK reduced slightly (such as 101.6), otherwise you might have a ram error occur once every 7 days or something like that.


Memory training
It has been difficult to find any decent information regarding what memory overclocking actually does in the case of DDR5 memory but i did find this explanation for DDR4, should be similar with DDR5:


I got the impression that changing the settings in bios to "long training" made the ram more stable but i haven't properly verified this yet. Still this is something you can play around with if you struggle to get your ram stable with acceptable performance.

I have heard that rebooting can make your memory unstable due to it being trained even if you don't actually change anything in bios (due to the memory being trained again in the next boot resulting in the memory working slightly differently) but i haven't verified that myself yet.


Memory stability table at 6461 MT/s 2x32 A-die
I was able to get it stable at 6448 MT/S stable in y-cruncher with better timings than anything i got stable at 6436 MT/s after i increased the DRAM and dram VDDQ voltage to 1.41

CPU VDD2: 1.41
CPU VDDQ: 1.26
CPU SA: 1.2


          stable  unstable
tCL       30      28
tRCD      38      36
tRCDw     37      36
rRP       36
tRAS      34      30
tRFC2     472

tRFCPB    372
tREFI     65535
tWR       96
tWR_MR    96
tWTR      8
tWTR_L    8      6(boot)
tRTP      15
tRTP_MR   15
tFAW      32
tCWL      28
tCKE      8
tCCD      8
tCCD_L    15
tCCD_L_MR 15

tRDRDSG   16
tRDRDDR   12

tWRWRSG   16
tWRWRDR   16

tRDWRDG   20
tRDWRDG   20
tRDWRDR   20

tWRRDSG   68
tWRRDDG   54
tWRRDDR   14

tWPRE     2
tRORE     2
tWRPRE    48     46?
tRDPRE    16
tPPD      2
tXP       6      4
tXPDLL    73
tCDDED    15
tAONPD    0
tREFIx9   255
tXSDLL    2048
tMOD      49
tZQCS     97
tZQCAL    752
tXSR      472
tCSH      40
tCSL      6
tCA2CS    8
tCKCKEH   11
tRFM      372
OREFRI    64

RTL initA 66
RTL initB 65
CHA/D1/R0 62
CHA/D1/R1 62
CHB/D1/R0 63
CHB/D1/R0 63
* not yet verified as properly stable.

This was tested with stressapptest since y-crunches failed to find stability issue with the following overclock (SAT later found instability after less than an hour):


At 6436 MT/s (and 1.4v dram voltages) i got the following table earlier.
           unstable  stable
tCL        28        30
tRCD       36        38
tRCDw      36        37
tRP                  36
tRAS                 36
tRFC       435

tRDRDSG    14        16

tRDWRSG    18
tRDWRDG    18
tRDWRDR    18

While this was likely stable timings were pretty lose and i later had trouble getting it stable with tighter timings (until the recent stable 6461 MT/s overclock).



Memory stability table at 6220 MT/s 2x32 M-die
These timings were posted by zero989 and i do not know how hard these have been tested for stability.



Framechasers: you need to find the voltage sweetspot for your CPU
Like me he found that there will be windows of stability for the memory controller voltages that shrink as you go up in frequency and that this varies between CPUs so it might not be stable if you copy voltages from someone else even if he/she has the exact same models of everything.

He also found out that applying the XMP profile might not even be stable at higher frequencies (such as 8000 MT/s).