[Hardware] Your AMD processor has it, but do you know what Infinity Fabric Clock is?

[Dark]

Already in the past we have discussed and defined what is AMD's Infinity Fabric, the method of interconnection of the different components that make up AMD Ryzen processors. This interconnection method also entails a new parameter in the processors, called FCLK or Infinity Fabric Clock, and that is what we are going to talk about in this article today: what is it and how can it be used to improve performance on the PC ?

As you probably already know, modern processors are no longer made up of a single chip literally speaking, but actually consists of a series of interconnected subsystems, such as the CPU itself with the cache or the memory controller. This method of interconnection, when we talk about AMD processors, is called the Infinity Fabric and has its own clock that dictates its operating performance.

What is Infinity Fabric on AMD processors?

Let's start at the beginning to put things in context, so let's define what Infinity Fabric is first of all. Also known by its acronym IF, we are facing a whole system interconnection architecture patented by AMD (this means that we cannot see it in Intel, for example) that is responsible for the transmission of data and control through the components that it has linked , which as we have put before as an example, can be for example the cache or the memory controller.

This connection architecture is used in all modern AMD microarchitectures since 2017 and not only in CPUs, since it is also used in GPUs. In essence, Infinity Fabric is the "technology" (although it really is an entire architecture) of interconnection of the internal components of an AMD processor, including the iGPU if you have one, the memory controller, the cache, USB controller and even the network card. If you want to know how Infinity Fabric works, we have an article dedicated to it.

What is the Infinity Fabric Clock or FCLK?
As we have explained, Infinity Fabric is really nothing but a communication bus that, as such, is controlled by a clock speed that dictates its operation, and this is precisely the Infinity Fabric Clock or FCLK. In the Zen and Zen + processors, the FCLK could not be configured independently but was associated with the speed of the RAM memory, which is why there were large differences in performance when opting for higher frequency RAM memories.

For example, a first generation AMD Ryzen processor required RAM modules of at least 3200 MHz speed to not significantly affect the performance of the Infinity Fabric.

FCLK

However, since the introduction of AMD's Zen 2 architecture processors this changed and now the FCLK has been decoupled from memory and can be controlled independently (at least on X570 chipset motherboards) from the system BIOS, being able to adjust its speed so that the system does not suffer such a performance penalty when the RAM memory is too slow.

Currently, in the Ryzen 5000 processors of Zen 3 architecture the FCLK is limited to a maximum of 2,000 MHz, which would correspond to the operation of 4,000 MHz in the RAM (remember that the RAM is DDR, Dual Data Rate).

Operating modes
Keep in mind that in AMD Ryzen processors, in addition to the normal clock frequency we have three others: Infinity Fabric Clock (FCLK) of which we have already spoken, the UCLK (memory controller speed) and MCLK (speed RAM itself). Infinity Fabric determines how fast the processor cores can communicate with each other when they are on a different die or with the I / O section of the processor itself.

By default, these three frequencies have a 1: 1: 1 ratio, or in other words, all three work in sync, so the FCLK will be linked to the RAM frequency as well, but as we have said before, now we have the option to modify this rule.

FCLK

Starting with AMD Ryzen 3000 processors, the use of a RAM of 3733 MHz or more causes the FCLK to reduce its speed, or in other words, that the ratio we have talked about before goes to 2: 1 with respect to to the MCLK. Thus, if we install 3733 MHz RAM, its frequency will be 1866 MHz and the FCLK will become 933 MHz.

Explained in other words, this means that the higher the speed of the RAM, the lower the performance of the Infinity Fabric, at least reached a certain limit (the 3733 MHz that we mentioned before).