Question Will using the 1st M.2 slot on Z790-E mobo affect GPU performance ?

[Daynhg]

Hi.

Can anyone help please.
New build.

Decided to get another NVME drive.
But I read that the 1st slot on this MB splits the bandwidth with the GPU.

I have my existing M.2 in the 2nd slot because of the above. (I havnt used the PC yet.) But as I am adding a second M.2, can I use the 1st slot, without any performance loss. On, gaming, VR, Blender, etc.

MB Z90-E
Asus ROG Strix 4080
Samsung 990 PRO 2TB PCIe 4.0 <-- there would be 2 of these.

One last thing.
I am thinking of returning the existing WD_Black SN850X 2TB M.2 2280 PCIe Gen4. - - for Samsung 990 PRO 2TB PCIe 4.0 x 2.

Does anyone please know if the 990 PRO gets realy hot, the board has fitted heat shields.

Thank you for any help.
It is really appreciated.

 

[dwd999]

Hi.

Can anyone help please.
New build.

Decided to get another NVME drive.
But I read that the 1st slot on this MB splits the bandwidth with the GPU.

I have my existing M.2 in the 2nd slot because of the above. (I havnt used the PC yet.) But as I am adding a second M.2, can I use the 1st slot, without any performance loss. On, gaming, VR, Blender, etc.

MB Z90-E
Asus ROG Strix 4080
Samsung 990 PRO 2TB PCIe 4.0 <-- there would be 2 of these.

One last thing.
I am thinking of returning the existing WD_Black SN850X 2TB M.2 2280 PCIe Gen4. - - for Samsung 990 PRO 2TB PCIe 4.0 x 2.

Does anyone please know if the 990 PRO gets realy hot, the board has fitted heat shields.

Thank you for any help.
It is really appreciated.

Page vii of the manual clearly states that "When M.2-1 is occupied with ssd device, PCIEX16(G5) will run 8x only." So if you can run your games with your graphics card at only 8x then using the first slot would be OK. But since you have 3 more available m.2 slots, why limit your graphics card?

 

[Daynhg]

Hi dwd999

Thank you for the reply.

TBH I was, and still am kind of confused.

This link (timestamped) shows this YT guy, who obviously knows what he's talking about, but kind of contradicts himself.

View: https://youtu.be/9DXovN4Bn5o?t=672

The top 2 slots are connected directly to the CPU, while the other 3 are to the MB.
Also in between saying you could, connect a gen 4 to the bottom 3 slots. And they would perform "almost" to full potential.

He also says "you wouldn't connect a gen 4 to these 3 bottom slots."

That is why I wondered if using the top slot with a gen 4 was fine?
Also would half bandwidth affect the GPUs performance in any way.

Does a 4080 need 16 to run at full capacity, or would only having 8 hit the GPU performance?

Thank you again for the help.

 

[Daynhg]

Quick follow up.

The post 1 down by VoraciousGorak, looks like he is agreeing with what you said.

If I assume by "chipset" hes refering to the motherboard.

Reddit - Dive into anything

www.reddit.com

 

[dwd999]

Quick follow up.

The post 1 down by VoraciousGorak, looks like he is agreeing with what you said.

If I assume by "chipset" hes refering to the motherboard.

Reddit - Dive into anything

www.reddit.com

I never watch youtube videos or read reddit since a lot of the people creating those videos are just saying anything that they think will get them clicks, and reddit people sometimes have reading comprehension problems. Anyway, the issue is: how many m.2 sticks are you ultimately planning on having? You could start with 4 sticks in M.2_2 and go up to M.2_5 before you would need M.2_1 for your 5th and last stick so why would you limit your GPU by using that slot unless you run out of other slots.

 

[CountMike]

Quick follow up.

The post 1 down by VoraciousGorak, looks like he is agreeing with what you said.

If I assume by "chipset" hes refering to the motherboard.

Reddit - Dive into anything

www.reddit.com

Other way around, refering to MB means chipset, that's where PCIe controller is. M.2 NVMe is on PCIe bus.

 

[thestryker]

Just to explain what's going on here: M.2_1 is PCIe 5.0 which is not supported by Intel CPUs so Asus is sharing PCIe lanes with the PCIe 5.0 x16 slot to provide this. It's a stupid design that no motherboard maker should have ever done.

M.2_2 is the one you should use for your primary SSD and then any of the other 3 slots for the rest.

edit: Reason for the chipset based ones not reaching "full" potential is partially that there's a slightly longer path which will degrade peak read/write performance potentially, but this is very minor. The other part is that the link between CPU and chipset is PCIe 4.0 x8 so if you had 3 drives connected and we're maxing them out they'd exceed available bandwidth and slow down (you may also see a slight slowdown maxing out 2).

 

[Daynhg]

Thanks guys.

dwd999​

Thank you for the help
"why would you limit your GPU by using that slot unless you run out of other slots."
Exactly what I thought. But I read that not even a 4090 needs more that 8 lanes.
I have no idea. what you say makes perfect sense, why take the risk.

CountMike​

Thank you for the confirmation of what that means.

thestryker​

I appreciate the breakdown.
And this.
"It's a stupid design that no motherboard maker should have ever done."
Even to a layman like myself, I wondered why they designed it like this.


The end result is, I am only looking at 2 x M.2 Gen4 SSDs 2 TB each.
That would be plenty for me.

Considering I have been using a SATA Samsung SSD for years with a read speed of about 550, and then going to 7000+ read (with any of these options.)
A slight loss, would still swamp what I am used to, be-it gaming, VR, <(Unity) or Blender sculpting.
And that is not even taking into account all the other hardware, being hugely faster than my old rig.

I have a SN850X 2TB in slot 2 now, hence the question.
And after all of the feedback on here. I will put the next drive WD, or Samsung, into slot 3.

Thanks guys.
I really appreciate the excellent help.