A few weeks ago we told you that the new AMD Ryzen 7000 processors were going to support DDR5 at 6 GHz in 1:1 mode, and that this would therefore be the “optimum point” that we could reach at most without the Infinity Fabric Clock ( FCLK) switch to 1:2 mode. It was not official information, that is, it had not been confirmed by AMD, but it had great credibility, and in the end has been endorsed by Robert Hallockdirector of technical marketing at AMD, albeit with some important nuances what we are going to see next.

In a round of questions and answers, the AMD executive has given all the details we need to know to choose the best DDR5 RAM to accompany our Ryzen 7000, and we have two important keys on the table: it is must work at 6 GHz, a level that is defined as “optimal” in relation to cost, stability, performance and availability by Hallock himself, and it will be better to use only two modules instead of fouralthough I am aware that for aesthetic reasons there are those who prefer to occupy the four DIMM slots of the motherboard.

We have already explained the issue of the frequency of DDR5 RAM and the Ryzen 7000. The first leaks indicated that if we used RAM memory at more than 6 GHz, the FCLK would go from working in 1:1 mode to working in 1:2 mode, which would cut the working frequencies in half, and that the FCLK speed would be 3 GHz by default. Well, that relationship between the speed of the RAM and the FCLK of the Ryzen 7000 seems to be wrong, since the default configuration of the FCLK will be 1,733MHz, and not 3 GHz as rumored.

Thus, if we use memory DDR5 at 5,200MHzthe Infinity Fabric Clock will work at 1,733MHzthe Memory Controller (UCLK) will do so 2,600MHz and the Memory Clock (MCLK) will run at 2,600MHz AMD has highlighted that some samples will be able to reach 2,000 MHz in the FCLK, but that this has not been a priority for AMD.

As for occupying only two DIMM slots, Hallock has explained that this is better because it is the natural nature of signal routing for DDR memory, and that it is very difficult to route four slots when running at high speed, as the signal integrity becomes “hit and miss”. To better illustrate this question, we only have to see the list of frequencies and occupied slots that AMD collects on its official website:

• 5200 MHz with one or two populated slots and one DIMM per channel.
• 3600 MHz with four slots populated or two DIMMs per channel.

Robert Hallock has pointed out that 1:1:1 mode is not so important anymoreand that the user will get the best results by leaving FCLK in auto mode and adjusting the RAM and memory controller speeds to maintain a 1:1 ratio between the two.

It will be very interesting to see what real difference did we end up with between using DDR5 at 5200 MHz and DDR5 at 6000 MHz with the new Ryzen 7000, and if the difference in performance between the two really justifies the higher cost or if the opposite happens in the end. With the DDR4 memory kits at 3,200 MHz, 3,600 MHz and 4,000 MHz, we found very small differences in the Ryzen 5000, so that situation may repeat itself.