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nejck
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z97 WS from ASUS, PCI Lanes question

Thu Sep 01, 2016 5:55 pm

Hello everyone,

First time posting here and I'd really appreciate the help! Free donuts for everyone!

My question is pertaining to the z97 WS motherboard from Asus. I am a little confused as to how the PCI-E lanes on these thing work - the max for z97 chipsets is 16 to the CPU and a couple are provided by the chipset for other extension cards besides the GPU (on a PCI-E 2.0 highway).

So, doing the math by Asus you get the option of having say 3 GPUs in a x16-x8-x8 configuration. Well, even if you have 32+ lane CPU how does the motherboard work with those settings if it support max 16 lanes (that is what I've read about the z97 online)?

Any clues would be greatly appreciate, gerbils :)
 
Captain Ned
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Re: z97 WS from ASUS, PCI Lanes question

Thu Sep 01, 2016 6:07 pm

I've got an Asus Z97-A (NOT 3.1) and it has 16 PCIe lanes that can all go to one GFX card or go 8/8 to two GFX cards. None of the PCIe 3.0 goodness flows to the third x16 slot.
What we have today is way too much pluribus and not enough unum.
 
Ryu Connor
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Re: z97 WS from ASUS, PCI Lanes question

Thu Sep 01, 2016 6:13 pm

PLX PEX8747 PCI-Express gen 3.0 x48 bridge chip. This chip wires out four PCI-Express 3.0 x16 slots, which auto-configure between x16/NC/x16/NC, x16/NC/x8/x8, and x8/x8/x8/x8, depending on how you populate the four slots.

https://www.techpowerup.com/200280/asus ... d-detailed
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Captain Ned
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Re: z97 WS from ASUS, PCI Lanes question

Thu Sep 01, 2016 6:14 pm

Ah, got it. I'm rocking a consumer mobo while the one in question is a workstation job. My bad.
What we have today is way too much pluribus and not enough unum.
 
nejck
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Re: z97 WS from ASUS, PCI Lanes question

Thu Sep 01, 2016 6:17 pm

Totally makes sense! Thanks for the help, both of you :)

I would like to ask an additional question about the PLX. Does it actually add additional PCI-E lanes via chipset ala making you hook up more than say the 16 lanes your supposed CPU supports (kinnda like Skylake and the extra PCI 2.0 on the z97)? If so, does that apply to faster x16 GPUs lanes too?

Also, pardon the idiotic typo in the OP. :)
 
Ryu Connor
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Re: z97 WS from ASUS, PCI Lanes question

Thu Sep 01, 2016 6:26 pm

nejck wrote:
Totally makes sense! Thanks for the help, both of you :)

I would like to ask an additional question about the PLX. Does it actually add additional PCI-E lanes via chipset ala making you hook up more than say the 16 lanes your supposed CPU supports (kinnda like Skylake and the extra PCI 2.0 on the z97)? If so, does that apply to faster x16 GPUs lanes too?

Also, pardon the idiotic typo in the OP. :)


It does not add in more lanes.  It takes the existing sixteen lanes of the PCI-E controller in the CPU and it rotates them slot to slot to slot via time division multiplexing.

Image
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nejck
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Re: z97 WS from ASUS, PCI Lanes question

Fri Sep 02, 2016 3:13 am

Sweet! Thank you for all your answers! :)

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