Question Installing a second PCIe card without compromising graphics card speed

Veteah

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Aug 5, 2015
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I realise this is quite possibly a daft question but I’ve been considering installing a WiFi expansion card and trying to learn a bit more how PCIe lanes work.

Motherboard: ROG STRIX 570-F

The motherboard has three PCIe slots, the top one of which has an RTX 3070 installed and the remaining two are empty. If it works the way I believe, if another expansion card were to be installed in the second slot it would reduce to speed to x8/8 ?

But it was installed in the third (bottom) slot, the graphics card would still be running at x16 but the WiFi card should run at x4.

Or I could just be talking complete gibberish and would the top PCIe card slow down to compensate?
 
I realise this is quite possibly a daft question but I’ve been considering installing a WiFi expansion card and trying to learn a bit more how PCIe lanes work.

Motherboard: ROG STRIX 570-F

The motherboard has three PCIe slots, the top one of which has an RTX 3070 installed and the remaining two are empty. If it works the way I believe, if another expansion card were to be installed in the second slot it would reduce to speed to x8/8 ?

But it was installed in the third (bottom) slot, the graphics card would still be running at x16 but the WiFi card should run at x4.

Or I could just be talking complete gibberish and would the top PCIe card slow down to compensate?
The spec page isn't very clear but it looks like you're right about how the PCIe slots work. The top two were intended for something like SLI which uses x8/x8 bifurcation, although you could use either alone in x16. The bottom slot is wired for x4 even though it will fit an x16 card physically.

The second slot wouldn't be a good location anyway since it will probably block at least one of a typical double-wide GPU's cooling fan intakes. If you have a 2 1/2 or triple wide card it's completely blocked anyway.

All a WiFi card should need is the unblocked x1 slot. But if you've a triple wide GPU the x4 slot would be better in order to avoid blocking it's intakes. Which one are you considering?
 
Last edited:

dorsai

Distinguished
I realise this is quite possibly a daft question but I’ve been considering installing a WiFi expansion card and trying to learn a bit more how PCIe lanes work.

Motherboard: ROG STRIX 570-F

The motherboard has three PCIe slots, the top one of which has an RTX 3070 installed and the remaining two are empty. If it works the way I believe, if another expansion card were to be installed in the second slot it would reduce to speed to x8/8 ?

But it was installed in the third (bottom) slot, the graphics card would still be running at x16 but the WiFi card should run at x4.

Or I could just be talking complete gibberish and would the top PCIe card slow down to compensate?
The RTX 3070 is a PCI-E Gen 4 card and will never use the bandwidth Gen 4 provides so I wouldn't worry at all about GPU speed when slotting something into the 2nd PCI-E slot.

That being said there are plenty of good WIFI expansion cards that work in the smaller x1 slots like this one


https://www.newegg.com/asus-pce-ax3000-pci-express/p/N82E16833320448?Description=pci-e 4 x1 wifi&cm_re=pci-e_4 x1 wifi-_-33-320-448-_-Product
 

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