RAM-speed vs CPU compatibility questions.

[Olle P]

This doesn't seem to be covered in the RAM FAQ.

All CPUs have listed what type and speed of RAM is supported. For example Intel's Skylake Core-series is listed to support DDR4 at 1,866 or 2,133 MHz (and only those speeds).

So what happens if you stick such a CPU to a capable motherboard and pair it with RAM that's set to a substantially higher speed? Do you get trouble accessing the RAM, as should be expected? No, you get a performance increase!
What does Intel mean by publicly stating a limited compatibility when reality shows a much broader acceptance?
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Then I have a side-note regarding XMP: The FAQ state that XMP stability isn't guarantied by the memory manufacturer. Yet the marketed speed for the memory I use (Crucial Ballistix Tactical, "2,666MHz") is achieved by activating XMP. With XMP off the RAM runs at a lower pace (2,400MHz).

 

[Olle P]

To make things even more unclear:
The RAM is supposed to be handled by circuitry in the CPU, the motherboard chipset should do nothing?
* If so it's even more puzzling that faster RAM can be used at all...
* Things get extra shady when you find that different motherboards featuring the same chipset (and CPU) provide different (theoretical) upper limits to the RAM speed supported...

 

[Olle P]

This is all about the technical aspects.
* What clock controllers/where are involved?
* What does it take to make it possible to set them at speeds above what's officially "supported"?
* At which interface(s) can one expect to run into trouble while trying to maximize the RAM speed?

Like:
- Do you need a "K" version CPU to "overclock" the RAM?
- Can you do it with a "B" or "H" type chipset?