Question Mobo and PCIE lane questions

Jun 18, 2020
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Hey everyone

I am building a new PC and i have a few questions regarding the "what happens" when i populate certain Mobos, these questions are regarding the Aorus B550 Master primarily but can extend to any other B550 Mobo's (Strix E and F). I am currently sitting with a Ryzen 3600X, AMD RX 5700XT and want to run 2 Nvme Drives with 32gb of 3200mhz+ ram without causing my GPU to downgrade from X16 to X8

  1. will using 4 sticks of Ram take additional PCIE lanes? running 4x8gb sticks vs 2x16gb sticks at 3200-3600mhz (mainly since all the boards im looking at are dual channel and not quad)
  2. on the B550 Aorus Master the top M.2 slot is PCIE 4.0 but the bottom 2 slots are PCIE 3.0 is there anyway to populate all 3 M.2 slots without the board dropping my GPU PCIEx16 down to x8 as described by OC3D on youtube. (can i run PCIE 4.0 x2 in the top M.2 slot and run PCIE 3.0 x2 in the bottom 2 M.2 slots for example to avoid the GPU dropping down to x8)
  3. even though the board has Wifi 6 built in is that taking up PCIE lanes? ( i do require Wifi ideally built in)
  4. If i use the PCIE 3.0 x4 Nvme in the PCIE 4.0x4 M.2 slot will it still use up all 4 lanes even though its the previous PCIE tech?
Thanks in advance guys!
 
Jun 18, 2020
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Hi, I use a Aorus X570 Elite Board which has 2 X m.2 PCi 4.0 slots which stay at PCi 4.0 even when I use a PCi 2.0 Graphics card, you are limiting the options you want to do by your motherboard choices.

PCi 3.0 has a speed limit of 4,000mb/s (for m.2)
PCi 4.0 has a speed limit of 8,000mb/s (for m.2)
The m.2 uses the same amount of lanes but they have different speed limits

For all info regarding what lanes do what go to the manufactuers website to look up what you want as there are too many to mention.
 
Jun 18, 2020
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2 - I know what you mean that if you used your 2nd gpu slot for say a 4 x m.2 card slot you will drop to X8 because the 2nd slot needs the lanes.
I saw a video on this on youtube (LTT) & to stop it dropping you would need a threaddripper motherboard with more lanes.
 
Reactions: rgd1101
Jun 18, 2020
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I kind of figure out the answer to my own question or the root of it by my worry about PCIE lanes.

PCIE 4.0 at x8 = PCIE 3.0 at x16 (disregarding other functionality benefits)

so it doesnt really matter if my GPU has been dropped to x8 (down from x16) as even a 2080ti approaches 2-3% saturation on a PCIE 3.0 x16
 
Jun 18, 2020
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If you scroll down this article I am sure you will see it is only the speed of the bus that has changed not the X8 / X16 lanes it uses to communicate.

https://www.pcworld.com/article/3400176/pcie-40-everything-you-need-to-know-specs-compatibility.html

Here is some more text from an article which I think is what you meant:

A 2080Ti pushes the limits of what a PCIe 3.0 x8 port will allow.
So, on a board with PCIe 3.0, running it in an x16 configuration makes the most sense.

With PCIe 4.0, however, there’s no need to run a graphics card with the full 16 lanes, because x8 mode will give more than enough for even a 2080 Ti. That means unlocking an extra eight lanes (or more in the case of lower-power GPUs) that can be used for a variety of additional purposes.
 
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