Not As What It Seems

After reviewing the full suite of benchmarks for both AMD and Intel systems, there is noticeable "underperformance" compared to other memory kits in the charts. This warrants a dedicated explanation. For those seeking a quick answer: the primary reason is that 24 GB DIMMs utilize larger dies, which results in increased cell refresh timings. This adjustment impacts overall performance in memory-intensive tasks.

The first thing to tackle is whether this may be a testing error. It is our due diligence to write honest and fair reviews. Therefore, to make sure it is not a test system error, or rather a set of bad data, system checks and benchmarks were tested for an A/B comparison with a previously tested DDR5-7200 memory kit. It was concluded that the "issue" must reside in the memory itself, or rather the XMP / EXPO profile. There is a very simple reason to this, and it has to do with the tRFC2 and tRFC-SB values which is applied when enabling the XMP / EXPO profile.

These tRFC2 and tRFC-SB values in their simplest description, determine in clocks cycles the time that must elapse during a refresh cycle. Essentially, the DRAM cannot be accessed while the refresh of memory cells is ongoing. With tRFC-SB being used for the "Same Bank" refresh, in which the same rules apply. In short, the higher these values are, the "longer" time (clock cycles) is spent being inaccessible to the system. This interrupt must happen due to the physical properties of the memory cells. Also known as volatile storage, it will lose the data in the event of power loss. If not periodically refreshed to ensure that it remains accurate, data bits are corrupted. On the flip side, if you set the value too low, the memory doesn't have enough time to fully refresh, resulting in data loss as well.

The 24 Gbit die (3 GB) is 50% larger than the 16 Gbit die (2 GB). To accommodate this increase in size, the tRFC2 and tRFC-SB values have been adjusted from 578-480 to 795-686, representing a 37.5–42.9% increase. This change results in more clock cycles being dedicated to cell refreshing. Unfortunately for high-performance enthusiasts, this is the trade-off, using 24 GB DIMMs comes at the cost of increased refresh latency, which can impact overall performance. Without manually setting these tRFC values, there is a clear regression in performance from brands like G.SKILL, Team Group and Kingston compared to their 16 GB counterparts inside the XMP/EXPO profile. The reason for these higher refresh times is because of the larger ICs. By following specifications set by either the DRAM manufacturer (SK Hynix in this example) or JEDEC organization, most of the XMP profiles are generally designed (programmed) using a linear progression model and scaling approach.

Below is a small example of the results of just changing the tRFC2 (795) - tRFCSB (686) values to 578–480 without adjusting the voltage or any other memory timings.

Counter-Strike 2 Results