PCIe 1x graphics card in PCH PCIe slot - will it work?

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namealreadytaken531

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Apr 27, 2016
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1,510
Hi,

I'm building a new PC and will use a secondary graphics card to be able to connect additional monitors. The performance of this card does not matter at all, it just needs to work.

Now the mainboard I'm getting is a Z170 one. So 16 PCIe lanes from the Skylake CPU (distributed to 3 PCIe 16x slots with possible configurations being 1x16, 2x8, and 1x8+2x4). And an additional 20 from the Z170 chipset (which itself connects to the CPU via DMI 3.0), distributed between onboard controllers, another PCIe 16x, and two PCIe 1x slots.

I'd prefer to keep the 16 PCIe lanes for the primary graphics card and for possible future expansion. But I cannot find information anywhere whether a graphics card in a non-CPU PCIe slot can even work. All I can find is that if you want to run SLI you need to use the CPU lanes in an 2x8 configuration.

I've contacted both ASRock and Intel support but have not heard back from them yet.
Has anyone tried to put a graphics card in a Z170 slot? Did it work?
 
Solution
Inkiad
For your information, the PCIE lane was part of north bridge, which was a separate chip outside the cpu. From sandy bridge onward, full functions of north bridge was integrated on the cpu itself. So, it will work. As it would have work prior to sandy bridge when you would install the gpu in slot which was connected to north bridge pch.
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Inkiad

Inkiad

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Jul 10, 2010
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I am not sure i understand your question. But anyway, PCIE 1x slot is a small slot. So check if your motherboard has the 1x slot open at the end, then you can install any PCIE card and it will work. Also the main gpu should be from same manufacturer. Like both should be NVIDIA or both AMD. Otherwise there will be driver conflict.
 
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namealreadytaken531

Commendable
Apr 27, 2016
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1,510


The secondary card is a Zotac Geforce 730 with a PCIe 1x connector. The mainboard also offers a flex PCIe 1x slot so even a 16x card could be put in that slot (as long as it doesn't need more than 25W).

The primary card is a Geforce 970, but the cards will not be used by the same OS but will be passed through to different KVM guests with the host OS not even loading drivers for the cards. So mixing manufacturers should not matter, but anyway, I'm not.

What I don't know is not if I can physically connect the card, but if it will work in a PCH lane slot. Basically not all PCIe lanes are created equal. For Skylake the CPU provides 16 lanes. In combination with Z170 these can be configured as 1x16, 2x8, vor 1x8+2x4. That is why there are so many boards offering these lane counts for their three 16x slots.
The Z170 chip is connected to the CPU with DMI3.0. It can connect additional controllers and cards via it's own 20 PCIe lanes (and USB). When those devices need to talk to the CPU they need to go through the Z170 first. And I don't know if graphics cards can operate in that way since they need more direct access to RAM than e.g. SATA or Ethernet controllers.

Hence the question: has anyone tried this/did it work?
 
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Inkiad

Inkiad

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Jul 10, 2010
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For your information, the PCIE lane was part of north bridge, which was a separate chip outside the cpu. From sandy bridge onward, full functions of north bridge was integrated on the cpu itself. So, it will work. As it would have work prior to sandy bridge when you would install the gpu in slot which was connected to north bridge pch.
 
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Solution
N

namealreadytaken531

Commendable
Apr 27, 2016
3
0
1,510
As it turns out ASRock agrees with you. I've heard back from them and they say graphics cards will work in PCH PCIe lanes without problems, but may run into serious performance issues when they need to compete with SSDs and other devices for the DMI3.0 bandwidth from the PCH to the CPU. So for my use case it should be fine, but for any graphics card that needs to deliver good performance a CPU PCIe lane should be used.

Anyway, my stuff came today, including the Intel 750 that will probably hog all the DMI bandwidth ;)
 
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