One of the changes Intel has made to the circuitry of its Gen 11 desktop processors, with the Rocket Lake-S architecture, is the renewal of the memory controller or Northbridge. The part of the CPU responsible for communicating the different cores with the RAM. These changes affect the choice of DDR4 modules for the PC. We tell you which is the best selection.
Gear 1 vs. Gear 2 and Rocket Lake-S
When it comes to communication with RAM, the memory controller in Intel’s Rocket-Lake-S architecture processors has two different modes of operation called Gear 1 and Gear 2. Gear 1 refers to the speed of memory clock or MCLK, while in Gear 2 mode this speed is halved.
Since DDR4 is a type of DDR memory, the memory clock speed is half that of the Gbps that is stipulated in the memory model, therefore the memory speed of DDR4-3600 is 1800 MHz. As for the communication of the integrated memory controller, IMC, with the DDR-3600 in Gear 1 mode it is 1800 MHz and in Gear 2 mode it is 900 MHz.
The reason why this is done is none other than to increase the clock speed of the memory interface which increases the power consumption, so reducing its clock speed can support a Faster RAM. Another reason is that when we increase the bandwidth of a memory with its processor, its latency also increases.
Unlike GPUs, processors do not have internal mechanisms to hide latency and RAM with increased latency due to increased bandwidth is counterproductive in terms of performance. With Gear 2 mode, Intel sacrifices bandwidth, but maintains low latency and thus maintains processor instruction performance.
BCLK and QCLK on Intel Gen 11
Now that we know the differences between the two modes, we must know when to activate Gear 1 mode or Gear 2 mode on the processor. Since Gear 2 mode at certain clock speeds has been shown to be not only the only way the CPU supports them, but in certain settings, Gear 2 mode performs better than the Gear 1 mode. Access via Gear 2 works with instruction latencies.
The Rocket Lake-S onboard memory controller operates with the following parameters:
- BCLK: The base clock speed of the IMC can be 100 MHz (100 x 1) or 133 MHz (100 x 1.33) in Gear 1 mode, while in Gear 2 mode it is 50 MHz ( 50 x 1) 0 of 66.67 MHz (50 x 1.33).
- QCLK: The clock speed multiplier, in Gear 1 mode, can go up to x 6 x 27. While in Gear 2, it can go up to x 63.
- MCLK: As we said before, it is the clock speed of the memory.
The formula for knowing both BCLK and QCLK to achieve a specific MCLK is as follows:
MCLK = BCLK * QCLK / 2
The reason for the division by 2 is that we are talking about a DDR memory, to make it more accessible we have decided to eliminate the division, because if we want to know if a DDR4-2400 memory is going to be compatible with Rocket Lake -S we just need to make sure that BCLK * QCLK has a result of 2400.
DDR4 not supported by Rocket Lake-S
From the information explained above, we can know which DDR4 memory is compatible with Rocket Lake-S, which BCLK can be used and which QCLK multiplier should be placed on the IMC in the BIOS of our PC. This is why we decided to make two tables, one to know how to configure the BCLK and the QCLK in Gear 1 mode, the other in Gear 2 mode.
The types of memory supported in Gear 1 mode are shown in the following table:
As you can see in Gear 1 mode, it is possible to connect DDR4-3600 memory by changing the BCLK to 100 MHz x 1.33 mode, which is higher than DDR4-3200 as the maximum clock speed that Intel guarantees that its Gen 11 CPUs support. Which is good news. As for DDR4-2800, it is not supported with BCLK in 100 MHz x 1 mode, and requires 100 MHz x 1.33 mode. Why have we marked it in orange? By the way, if you’re lucky you can get one of the Rocket Lake-S with a fully functional x 28 multiplier.
Regarding Gear 2 mode, the table is as follows:
In Gear 2 mode, DDR4-4200 is the type of DDR4 with the highest speed supported, but for this it is necessary to enable the BCLK in 50 MHz x 1.33 mode. Otherwise we will be limited to DDR4-3100. Since Gear 2 mode has lower latencies than Gear 1 mode, we recommend using it. Not only to be able to use memory beyond DDR4-3200, which is the fastest type of memory officially supported, but also due to the fact that Gear 2 has higher performance.
How to change BCLK and QCLK on Rocket Lake-S?
It’s very simple, you just have to do it in RAM, many BIOSes directly adapt the speed of the BCLK without further complications. Others, on the other hand, will require you to manually modify the BCLK and the QCLK. In any case, it should not be forgotten that if you update the DDR4 memory of your PC with Rocket Lake-S then you must make the corresponding modifications in the BIOS to activate a Gear or another In Rocket Lake-S.
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