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ROG Maximus Z690 Hero - M.2_1 slot & PCIEx16_1 bandwidth?

ttaneff
Level 8
As there is very contradicting and unclear information, both for different models of the MAXIMUS boards and the lane sharing, my question is simple:

What will happen if I populate the M.2_1 slot (top) with a PCIE(G4) SSD drive, while having a 16x(G4) GPU in PCIEx16_1 slot on the MAXIMUS Z690 HERO with 12th gen 12900k CPU ?
a) The M.2_1 will use 4x lanes Gen4 to the CPU and the GPU will stay at x16 Gen4/Gen5
b) The M.2_1 will use 4x lanes Gen4/5 shared with the GPU, dropping the PCIEx16 slot to x8 Gen4/Gen5

I honestly don't get it as the manual says the M.2_1 slot is using the dedicated 4x PCIE4.0 lanes of the z690/12th gen, while topics about the EXTREME models suggest the M.2_1 is Gen5 capable and paired with the GPU lanes which are total of 16x PCIE5.0 for z690/12th gen.

What is the "truth" - is there a M.2 slot where I can get maximum performance from the SSD while keeping the GPU at x16 on the MAXIMUS HERO board?

Thanks!
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19 REPLIES 19

AwenMilano
Level 10
hi there, i use z690 hero board too,
may i ask you about xmp?
do you have trouble with xmp on this board?
i use hero + g.skill 6000mhz + i7 12700kf
since dec until now xmp 6000 still unstable.
use xmp 1 but reduce the speed to 5600 now is stable

Nate152
Moderator
Hi ttaneff,

Welcome to the ROG forum.

M.2_1 (A) will use the cpu lanes and will drop pciex16_1 to x8.

B and C uses the chipset lanes, use these to keep pciex16_1 to x16.

92907

Nate152 wrote:
Hi ttaneff,

Welcome to the ROG forum.

M.2_1 (A) will use the cpu lanes and will drop pciex16_1 to x8.

B and C uses the chipset lanes, use these to keep pciex16_1 to x16.

92907



This is wrong info. The PCIE SSD will run at 4X and the graphics card at 16X as the 12900K has 20 lanes.

Graphics card would only drop to 8X if you put something in the second PCIE 8X slot.

Obviously this subject (PCIE bifurcation / CPU Lane reservation) is a very tricky one when it comes to motherboard design.
Thanks for the info - I will have to do it "the old school" way - borrow an NVMe SSD and perform trials before investing in PCIE4.0 M.2 drive 😉

@Attachment 92907
Regarding the XMP - I use Corsair DDR5200 @ 5200 Mhz without problems - could squeeze 5600 (XMP with target 5600 at the AI Tuner) but didn't perform heavy testing. This obviously doesn't help you much as I'm not experienced OC-guy and run the system pretty much at "average". Might be the RAM modules as well as the chipset/board - DDR5 has quite the temper regarding timing and OC response - you might have luck searching for other users experience with the same DRAM for the "sweet spot".

Spicedaddy wrote:
This is wrong info. The PCIE SSD will run at 4X and the graphics card at 16X as the 12900K has 20 lanes.

Graphics card would only drop to 8X if you put something in the second PCIE 8X slot.


I had the same question a while back
I have 1 m.2 NVME SSD that i put in m.2_1, an nvidia rtx 3090 in Pcie16_1(Gen5), with a 12900k
I put a sound card in the 3rd slot which is Pcie16(Gen4) - but I was told since it's rated only for Gen4, it doesn't take lanes away from Pcie16_1(G5) or Pcie16_2(G5) - is this true?
Is the 3090 still getting pcie gen4 x16 speed as well?

in Samsung Magician, It says I'm running the SSD at Gen4 x4 speeds from what i remember seeing.

MikeJeffries wrote:
I had the same question a while back
I have 1 m.2 NVME SSD that i put in m.2_1, an nvidia rtx 3090 in Pcie16_1(Gen5), with a 12900k
I put a sound card in the 3rd slot which is Pcie16(Gen4) - but I was told since it's rated only for Gen4, it doesn't take lanes away from Pcie16_1(G5) or Pcie16_2(G5) - is this true?
Is the 3090 still getting pcie gen4 x16 speed as well?

in Samsung Magician, It says I'm running the SSD at Gen4 x4 speeds from what i remember seeing.


The sound card in the third pcie slot runs at x4 from the chipset. Your RTX 3090 is running at x8 by having an ssd in the A slot, you can see this in the bios.

Running at x8 isn't too big of a deal, pcie 5.0 x8 is like pcie 4.0 x16.

Nate152 wrote:
The sound card in the third pcie slot runs at x4 from the chipset. Your RTX 3090 is running at x8 by having an ssd in the A slot, you can see this in the bios.

Running at x8 isn't too big of a deal, pcie 5.0 x8 is like pcie 4.0 x16.


3090 is a pcie 4.0 gpu, not 5.0.

Nate152 wrote:
The sound card in the third pcie slot runs at x4 from the chipset. Your RTX 3090 is running at x8 by having an ssd in the A slot, you can see this in the bios.

Running at x8 isn't too big of a deal, pcie 5.0 x8 is like pcie 4.0 x16.


Where in the bios can i see what the gpu is running at (x8 or x16)?

MikeJeffries wrote:
Where in the bios can i see what the gpu is running at (x8 or x16)?


I don't think you can see it in BIOS.


CPU-Z ( I think the Motherboard tab...) will show the PCIE speed.