Hello everyone,
I’m trying to decide between AMD x470 and Intel Z370
What has come to my attention is that AMD Ryzen CPUs have dedicated 4x PCIE lanes to one M.2 SSD while Intel CPUs are linked to the M.2 slot through the chipset, which in turn is connected to the CPU by 4x PCIE lanes that are shared among all SATA drives too.
I can tell that this is important to me: my usual workload would benefit from the full performance off my M.2 SSD as well as 2x SATA SSDs simultaneously, and given the performance of current gen Samsung PRO line of SSD the peak throughput should exceed the DMI 3.0 specification of 3.93GB/s.
Am I understanding this correctly?
If I were to go for an i7-7820X instead, since it has more PCIE lanes, must I connect the M.2 SSD to a PCIE adapter to bypass the chipset bottleneck?
Or should I just go for AMD Ryzen instead, since I’m not planning to use a dual graphics card setup anyway?
Edit: clarity
Yes this is correct. You must use one of the lanes connected to the CPU, typically one of the physical x16 slots.
A Samsung nvme won’t be bottlenecked by the DMI 3.0 link in the real world,but like you said, if you do other stuff simultaneously it can cause some bandwidth issues.
A Ryzen 2700X is a better pick than a 7820X imo, unless you need quad channel memory, in which case you should just go threadripper instead.
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There you have absolutely no bottleneck on the m.2 side…
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Dang, this is a serious limitation of intel processors.
Also it isn’t well reported at all, it took me a while to figure these things out.
I’m surprised those very expensive processors do not have motherboard with M.2 slots communicating directly to the CPU.
Why are manufacturers hiding this important information?
They aren’t hiding it, but understanding a chipset can be a bit complicated at first.
Think of the chipset itself as a PLX chip.
Intel hasn’t had more than x16 lanes from the CPU on LGA115X.
You can still use a riser card and run it from one of the x16 slots, while this will reduce the GPU to x8 lanes it won’t bottleneck the card.
But looking at the i9-7980XE for example, says the “Max # of PCI Express Lanes” is 44. However apparently there are no x299 motherboard that have a M.2 slot directly connected to those lanes, the only way to connect an M.2 drive bypassing the chipset is to connect it through a pcie adapter card and that would take up a slot and space.
It’s not my situation for sure but it seems rather dumb…
I believe the ruleset of X299 might not allow for M.2 slots to be directly connected to the CPU. But I’ll have to get back to you on that.
Okay there are a few X299 boards that has an M.2 slot connected to the CPU.
Aorus Gaming 7/9 seem to have one slot that goes to the CPU.
Asus has some high end boards where you put your M.2 into a DIMM.2 riser and it’s connected to the CPU.
The X299 chipset is a total clustefuck to wrap your head around due to them supporting x16, x28 and x44 lane CPUs.
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That’s interesting.
I looked into those DIMM.2 risers. They look damn weird, I read about them being so tall they often hit top-mounted radiators in cases like the Fractal Define R6 