Tweaking for Speed

With testing out of the way, it is time to see if this memory kit has any additional headroom. For Intel, we start off by using the XMP profile and increasing the frequency until the loss the system stability. After finding what can be accomplished without changing any of the timings or voltage, the second step can begin. This is where we go for the maximum frequency and lowest possible timings. Voltage modification above the XMP profile is allowed. After all, this is overclocking!

Intel's 11th Gen Intel Core processor paved the way for things to come. The introduction of the memory controller Gear Ratio allowed the system memory to run in synchronous 1:1 mode (Gear 1) with the CPU memory controller, or in a 2:1 ratio (Gear 2). With the release of Intel's 12th Gen Alder Lake based processors came DDR5 support and the additional 4:1 ratio (Gear 4).

It is generally considered that between 3600 and 4000 MT/s is the upper limit for Gear 1 support when using a Alder Lake (12th Gen Intel) CPU. This of course is partially dependent on the CPU memory controller and supporting voltages related to memory. In rare instances, higher-end motherboards can increase this slightly and offer better overall compatibility due to shorter trace length, PCB layer count and a better memory training algorithm. For instance the Intel Core i9-12900K used for these memory reviews maxes out at DDR4 4133 MT/s for single-rank memory. 4133 MT/s is quite a unlikely occurrence judging based on the sheer number of forum posts of many users struggling to get 3800 MT/s stabilized. It is safe to say that anything greater than 3600 MT/s using Gear 1 will often require a bit of hands-on tuning.

Since DDR5 has a higher operating frequency and a dual 32-bit data bus, synchronously operating it in 1:1 does not function at all. So far there have been no confirmed reports of this working for DDR5. That only leaves 2:1 Ratio and above as a viable option for any DDR5-based setups. The motherboard should automatically switch to the 2:1 ratio for both DDR4 and DDR5 above 3600 MT/s. If all else fails, you can manually enforce Gear ratios in the BIOS as well. With this information on hand, we can deduce that Intel 12th generation processors using DDR5 in theory will benefit the most from the highest-possible frequency, until the 2:1 ratio is not longer possible. At that point the cycle starts over again with a new 4:1 ratio and even higher frequency system memory.

Those looking to overclock on a Intel platform will generally find a hard barrier around 6600 MT/s using the Intel Z690, as many 4-slot motherboards do not support higher speeds. Only a handful of motherboards are designed to support 6666 MT/s and up. These are the ASUS Z690 Apex, Gigabyte Z690 Tachyon, MSI Z690 Unify-X, ASRock Z690 AQUA OC, and EVGA Z690 Dark.

Caution is advised with DRAM voltage over the rated XMP profile. Direct airflow or a waterblock may be necessary for long-term stability. This extends to the CPU as well. Raising the integrated memory controller voltage (vDD2), System Agent (SA), and VDDQ_TX above Intel specifications may cause irreparable damage. Please proceed with care and do research before attempting this. Do not copy and paste values without understanding the impact first, especially if simply taken from screenshots posted on Discord or Reddit.


For thermal testing, Karhu stress test software was used for 30 minutes, after which both DIMM temperatures from the SPD hub sensors are averaged together. Testing was performed with and without a fan at the XMP of 1.35 V and an overclocking voltage of 1.435 V. DDR5 Samsung memory ICs are susceptible to temperature related system errors as well. Since more voltage is necessary for higher frequency memory, I caution against overclocking without a fan directly placed on the memory, or at least good case airflow. Otherwise, unexpected stability issues may occur as the memory warms up.

Overall Corsair did okay without a fan directly on the memory. 1.435 V is the highest value allowed due to PMIC being locked. The true thermal capabilities of this heatsink design is left unanswered at this time.

Intel Results

This first generation of Samsung based DDR5 memory has been slow to enter the market. The overclocking community has also shrugged it off because of the mediocre performance in comparison to SK Hynix. While the current Samsung DDR5 (K4RAH086VB-BCQK) ICs cannot reach the same performance metrics, it certainly is able to keep up when it comes to adjusting the secondary and tertiary timings. These are Samsung B-Die as well, but not to be confused with DDR4 B-Die, widely known as the King of DDR4 overclocking.

The first step was to figure out the highest frequency possible using the XMP profile, without adjusting the voltage. The results are underwhelming and the memory would not boot without loosening up the primary timings to 40-40-40-76. The next step was to figure out the highest frequency this kit could achieve with more voltage applied. Without the datasheet for these ICs, at this time, it is recommended not to exceed 1.45 V for daily use. In this instance, the PMIC controller was locked and did not allow for over 1.435 V. Using that voltage, 6400 MT/s was mostly stable using the XMP timings of 36-36-36-76. Every so often using these timings, it would throw an error during the memory test, meaning it wasn't truly stable and further tweaking of the timings was required.

Due to the restricted DRAM voltage, going up in frequency was short lived. Instead 6000 MT/s was used as a base and all the timings (primary, secondary and tertiary) were adjusted to boost the overall performance. The screenshot is the final results. Lowering any of these values further would result in either system instability or failure to boot. The only exception to the rule "lower is better" is tREFI. This was raised from 66535 (default) to 1.5X (99802) for a longer duration between cell refreshes. Higher values resulted in memory errors as well.


Note: All memory overclocks passed Karhu stress test 2000% or more.





Overall, if you have the patience to tweak this memory, it can be worth the time invested. That being said, understand no overclock is guaranteed and stability issues may occur if the memory gets too hot. This was certainly the case here. Without a fan directly on the memory, system errors was not uncommon to see while working on the memory sub-timings.