I'm a little confused about ryzen incompatibility with memory. It doesn't just work with any dd4 that fit into the motherboard? Does it require the higher speeds or would 2400 work?
I know there's a QVL somewhere, but I surprisingly can't find it anywhere, just people talking about it.
These are the memory speeds officially supported by Ryzen:
If you stick to that, you should have no trouble at all.
However lots of people are wanting to use faster memory speeds than that, which is where things get tricky.
In the old AGESA updates, memory sub-timings were hard-coded by AMD.
These sub-timings were very tight, which meant that basically nothing but Samsung B-Die RAM kits could handle them - and even then, possibly only with two DIMMs on most motherboards.
With the AGESA 1.0.0.6 update sub-timings are relaxed now, and you are able to adjust the sub-timings manually in the UEFI.
So many kits which could not handle high speeds with the very tight sub-timings that were being forced before, are now able to use more relaxed timings and work at their rated speeds.
Additionally, new multipliers were enabled, so that intermediate frequencies between the previous presets and above them can now be used.
Previously, the multiplier went in 1.33x increments, and maxed out at 16x. (100 x 16 x 2 = 3200MT/s)
Now they have added 2/3 increments, and it tops out at 20x. (100 x 20 x 2 = 4000MT/s)
However that does not change the fact that the memory controller used in the current Ryzen CPUs is only designed to handle 3200MT/s maximum, or the fact that any speeds higher than the slide posted above are still overclocks and not guaranteed.
There's just a much better chance that higher speed memory kits will now work at their rated speed after the AGESA 1.0.0.6 update.
The QVL list is a "qualified vendor list" which is motherboard specific.
Basically this is a list of components that the manufacturers have actually tested and verified as working with that motherboard.
Any hardware which meets the specs
should work, but only hardware on the QVL list is certified to work.
AMD did also post a list of kits which should work, but I would not accept that as a guarantee unless they are also on your motherboard's QVL list.
I think I have been lucky, but by buying a 2x8GB 3600MT/s memory kit from Corsair which was a Samsung B-Die kit, I had no trouble running it at 3600MT/s right out of the box with my Crosshair VI.
However 3600MT/s speeds required a BCLK overclock, since the multiplier was previously locked to 16x. In my case that was 122.6 x 14.67 x 2 = 3596MT/s, which was more stable than 112.4 x 16 x 2. (16x had cold-boot issues)
Now that the 18x multiplier is unlocked, it should be possible to avoid a BCLK overclock and run 100 x 18 x 2 for 3600MT/s - if the IMC can handle it.
But I've since swapped that memory out for a 4x8GB ECC kit that runs at 2666MT/s in all four slots, and haven't had any stability issues at all - despite Ryzen only officially supporting 1866MT/s in that configuration.
Now none of this is really a problem, or unexpected.
It's just that this is AMD's first platform capable of DDR4 support, while Intel has been supporting it since 2015.
So Intel have had several revisions of memory controllers, and you now have boards that support upwards of 4200MT/s.
You still have the problem of kits rated for that speed being unable to support it stably unless you buy a high-end motherboard and get lucky with your CPU's IMC, it's just that most people aren't buying the bleeding-edge of DDR4 speeds.
And while not all CPUs may support 4200MT/s+ Intel does seem to generally support 3200MT/s+ better than Ryzen right now.
Most people with Intel CPUs are not running kits at the speeds that people with Ryzen CPUs are having trouble with though.
People forget that Skylake is only rated for 2400MT/s kits, and 2666MT/s for Skylake-X.
I think part of it was the "scare" when Ryzen launched, where it turned out that memory speeds affect the cross-CCX latency, but we now know that you quickly see diminishing returns for that above 2666MT/s.
Not that faster memory is worse, but that's what I would recommend you seek as a minimum speed for optimal performance.
I've also seen a lot of people on overclocking forums with 2133MT/s or 2400MT/s kits complaining that their memory won't run at faster speeds.
Memory manufacturers seem to be binning the higher-speed kits now, so anything which doesn't pass is sold as a lower speed kit.
There's no guarantee that when you buy slower components that it will overclock and run at a faster speed. That's why it's not being sold at those speeds.
There's no guarantee that the same kit would run at a higher speed on an Intel platform either.
