Surprisingly High Latency Discovered During Alder Lake Test With DDR5-6400 Memory

Jason R. Wilson

Twitter user @harukaze5719 posted this on their Twitter feed three days ago:

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The image posted is of a leaked benchmark of the new Alder Lake from Intel that was appeared to be running with its newest Gear 4 setting. The benchmark shows that it was using an Intel Core i5-12600K 10-core CPU with DDR5 memory. The CPU was running the AIDA64 memory and cache test while the DDR5 memory was utilizing DDR5-6400 settings, with a result of up to 90GB per second. What was surprising was that the latency on memory was processing at 92.5ns.

The Twitter user followed the image with further proof of the testing:

The latency is equaled to AMD's first generation Zen architecture, which had continued problems with memory structure during its first release.

Intel's Rocket Lake series was the first adaptation of gear modes — Gear 1 and Gear 2 — and saw improvements on memory support with latency taking a hit. Gear 1 was the default setting for Rocket Lake that processed both memory controller and RAM at the same frequencies, but also showed extremely low latency levels on the system. Gear 2 setting was created to reduce the memory clock and cause the memory controller's clock to run at 50% less frequency (a ratio of 2:1). This would then cause the system to show increased bandwidth at the higher frequency caused by the drop of memory processing.

Tom's Hardware had tested Rocket Lake shortly after release, and when looking at the results, they noticed an interesting issue with Gear 2 settings:

When we tested both gears in our Rocket Lake review, we noticed Gear 2 took a noticeable toll on system latency, directly impacting gaming performance. We tested a Core i5-11600K with Gear 1 mode featuring DDR4-2933 RAM, and DDR4-3200 RAM for Gear 2. Despite the faster memory speeds on Gear 2, we found that Gear 1 was consistently faster, with 5% better gaming performance. The memory latency results showed a similar trend, with 59.3ns for Gear 2 mode and 52.3ns for Gear 1. The latency results would be even more pronounced if both configurations ran at the same RAM frequency.

Gear 4 setting is slated to remove 25% of the memory frequency, allowing for the CPU to allow for high-speed memory but with an increased latency loss.

So if the leaked latency results are true, with Gear 4 nearly doubling the amount of memory latency of Gear 1, then that setting will probably be quite useless for PC gaming and for other consumer-based applications. Generally, system latency is far more important than memory bandwidth, with only a couple of memory-hungry apps actually breaking that rule. So we'll have to see how these changes materialize once Alder Lake launches later this year.

No one has complete knowledge of the highest level of frequency on memory on the newer and high dollar DDR5 memory, outside of the knowledge that it is capable of reaching 12600MT/s. The speculation is that Gear 4 mode will shine in respect to those speeds.

Source: @harukaze5719 on Twitter, Tom's Hardware

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