Intel’s new 11th generation CPUs have been available for purchase for a few weeks now, albeit only recently officially. And so I also got hold of an i7 11700K and took a look at what innovations we can expect with the new generation, especially with regard to RAM tuning and overclocking. Unfortunately, I couldn’t present any reliable results so far, since new microcode and thus BIOS versions were released recently, even for Z590 mainboards, which have actually been on the market since the beginning of the year. But anyway, today is finally the day!
In today’s article I would like to take a look at what has changed with the 11th generation in terms of overclocking RAM, because although Rocket Lake still uses the same 14 nm manufacturing process as since Skylake, Intel has changed the internal architecture quite a bit. Primarily fewer and larger cores, with more power and support for AVX512, and a reworked memory controller should do the trick for this generation and bring the gaming crown back to Intel. Whether Intel has succeeded in this, Igor reveals in his big Rocket Lake review, with partly surprising findings!
Eyes open when selecting gears!
Of particular interest with the new CPUs is what has changed with the Integrated Memory Controller (IMC) and what new peculiarities need to be considered when overclocking memory with Rocket Lake. As it was already known in advance by numerous sources, Intel now also uses a gearing, i.e. a translation between memory controller (IMC) and RAM, in the form of Gear 1 (1:1) and Gear 2 (1:2), very similar to the 1:1 and 1:2 modes on AMD Ryzen CPUs between UCLK and MCLK.
The principle is similar to the gearbox in a car, except that you only have 2 gears and cannot change gear while driving, but have to decide beforehand. If we stay in this analogy, for low speeds and better response the first gear is better suited, but this can only be used until the memory controller or motor in our example reaches its “rev limit”.
This “rev limit” is made up of several factors and is reached with Rocket Lake in Gear 1 between DDR4-3733 and 3866. Officially, Intel specifies the supported maximum frequency in Gear 1 even a good bit lower, namely DDR4-3200 on the i9-11900 K(F) SKUs and DDR4-2933 on all other SKUs. If we look at what else the memory clock is composed of, namely the reference clock (depending on the base clock) and the QCLK ratio, then the limit also becomes more tangible.
The basic formula for the RAM clock is as follows:
MCLK = Reference Clock x Gear x QCLK Ratio / 2 (Dual Data Rate)
Of course, as always, we have to keep in mind that “DDR” stands for Dual Data Rate and the actual clock rate is only half. As with previous generations, the reference clock of the memory controller offers a choice between a multiplier of 1.00 and 1.33 and thus an effective clock of 100 or 133 MHz. Multiplied by this, on the one hand, is the new gearing – i.e. the factor 1 or 2 – and, on the other hand, the QCLK ratio just mentioned, a number between 6 and 31. And exactly this QCLK ratio depends on the silicon lottery and determines how high the IMC of a particular CPU can clock the RAM. Depending on the chip quality and the RAM used, this is a maximum of 28-29.
So faster RAM clock rates can only be achieved in the Gear 2 by roughly halving the clock rate of the memory controller and its load. Purely arithmetically you can then reach the double clock rates with this second gear, namely DDR4-7466 to DDR4-7533. Of course, these are only theoretical values, which cannot be achieved with DDR4 in daily operation, but the scale is already shifted upwards with this new IMC design, also in preparation for upcoming CPU generations and DDR5.
Let’s take a look at this with a few theoretical examples:
DDR4-3600 = 1800 MHz:
- 100 MHz x 1 x 36 / 2 (practically does not work, because QCLK ratio cannot be greater than 31)
- 100 MHz x 2 x 18 / 2 (works)
- 133 MHz x 1 x 27 / 2 (works)
DDR4-4000 = 2000 MHz:
- 100 MHz x 1 x 40 / 2 (practically does not work, because QCLK ration cannot be larger than 31)
- 100 MHz x 2 x 20 / 2 (works)
- 133 MHz x 2 x 15 / 2 (works)
So if you want to run your RAM at DDR4-4000 for example, you have to choose the Gear 2 mode with Intel Rocket Lake, there is no way around it and no binning either. We’ll take a look at how this affects performance and what other effects single and dual rank configurations can have in the following pages. But besides the gearing, there are a few other new and tweaks that we’ll get to in a bit.