Question How does the Asus Rog Strix Z390-E handle the PCIeX16 slots ?

Aug 4, 2020
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Hi,

Would populating only the 2nd PCIeX16 slot of the Asus Rog Strix Z390-e gaming with the graphic card affect perfomances in any way ?
The graphics card is Sapphire Nitro+ 5700 XT.

I found this information but it doesn't allow to understand if the mobo will treat the graphics card as a X16 or a X8 if it's plugged in the 2nd slot since it's the 2nd slot, or if it will detect that there is only one PCIe slot populated and therefore give it the full X16 bandwidth :



"The two reinforced slots share the CPU’s sixteen lanes of bandwidth via automatic x8/x8-mode switching whenever a card is detected in the second slot. Meanwhile, the third x16-length slot is fed by the PCH with only two lanes by default"

Thanks !
 
Aug 4, 2020
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Don't think so. Manual describes both slots as being x16.
True,
But I'm still confused with this explanation I found in a different forum (true or false..)
"The two reinforced slots share the CPU’s sixteen lanes of bandwidth via automatic x8/x8-mode switching whenever a card is detected in the second slot."

Literally, this means if something is in the second slot, the mobo will switch to x8, no matter if there's something in slot 1 or not ! :oops:
But yeah I don't know :D
 

kanewolf

Titan
Moderator
Hi,

Would populating only the 2nd PCIeX16 slot of the Asus Rog Strix Z390-e gaming with the graphic card affect perfomances in any way ?
The graphics card is Sapphire Nitro+ 5700 XT.

I found this information but it doesn't allow to understand if the mobo will treat the graphics card as a X16 or a X8 if it's plugged in the 2nd slot since it's the 2nd slot, or if it will detect that there is only one PCIe slot populated and therefore give it the full X16 bandwidth :



"The two reinforced slots share the CPU’s sixteen lanes of bandwidth via automatic x8/x8-mode switching whenever a card is detected in the second slot. Meanwhile, the third x16-length slot is fed by the PCH with only two lanes by default"

Thanks !
It will treat the 2nd slot as x8. Only the first slot is x16 according to the specs.
Both are x16 slots and running either independently should work at maximum bandwidth.
They maybe physically x16 slots but that does not guarantee that they are electrically x16 slots.
 
Reactions: CapybaraBoomBoom
Aug 4, 2020
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It will treat the 2nd slot as x8. Only the first slot is x16 according to the specs.

They maybe physically x16 slots but that does not guarantee that they are electrically x16 slots.
Wow thank you !
I wonder where you found that specific answer in the specs, I couldn't figure it out !
 

kanewolf

Titan
Moderator
Wow thank you !
I wonder where you found that specific answer in the specs, I couldn't figure it out !
Your picture posted in the original post. The fist statement says there are three slots. There are multiple possible configurations of PCIe lanes x16/0/2 for example. The first slot can have 16 lanes the second 0 the third 2. OR there could be an x8 and x8 configuration. NOTICE that there is never shown an x0 and x16 configuration.
 
Aug 4, 2020
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Your picture posted in the original post. The fist statement says there are three slots. There are multiple possible configurations of PCIe lanes x16/0/2 for example. The first slot can have 16 lanes the second 0 the third 2. OR there could be an x8 and x8 configuration. NOTICE that there is never shown an x0 and x16 configuration.
Ohhh that's how !
Ok thank you I didn't know how to read this like you did 🙏🏻
So you're really sure ? 2nd slot = only always 8 ?
 

kanewolf

Titan
Moderator
Ohhh that's how !
Ok thank you I didn't know how to read this like you did 🙏🏻
So you're really sure ? 2nd slot = only always 8 ?
I don't have any hands on experience. Reading the specs and knowing that they have to switch an x8 to the second slot, my belief is that is how the second slot is wired, as an x8 electrically, x16 physical slot. I am fairly confident in my answer. Unless you have a 2080 or similar video card, the difference between x8 an x16 may be negligible.
 
Reactions: CapybaraBoomBoom
Aug 4, 2020
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I don't have any hands on experience. Reading the specs and knowing that they have to switch an x8 to the second slot, my belief is that is how the second slot is wired, as an x8 electrically, x16 physical slot. I am fairly confident in my answer. Unless you have a 2080 or similar video card, the difference between x8 an x16 may be negligible.
Hi Kanewolf
Yes what you say seems to make sense
indeed the question is to quantify how much of a palpable difference the position will make
I want to put it further away so it's not against the cpufan otherwise it's almost touching it
but thanks indeed I don't know if there is a way to know for sure....
 

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