Question PCIe lane availability

[cassidydotdk]

I'm trying to work something out. I'm sorry, I know these types of questions come up a lot - but the workings of PCIe lanes is really confusing

So anyway. I have (of what I think is relevant):

• Asus ROG Strix Z390-E Gaming motherboard
• I9-9900K CPU
• 1 RTX 2080ti
• 2 M2 Samsung 970 Pro NVMe

And this is fine.

My motherboard documentation states, for PCIe slots:

2 x PCIe 3.0/2.0 x16 (x16 or dual x8)
1 x PCIe 3.0/2.0 x16 (max at x4 mode)
3 x PCIe 3.0/2.0 x1

Now I was told by someone (can't find a reference) that in this configuration, I am using all of my 24 PCIe lanes (where does that number come from?) - 16 lanes for the 2080ti, and 4 lanes for each of the M2 drives.

Is this true?

What I wanted to do, was slot in a 10 Gb card:
- ASUS XG-C100C (PCI-E x4)

But according to my friend, this won't work due to lack of lanes. Or at best I would degrade the performance of my 2080ti.

Can someone shed some light on this, please?

 

[jimmysmitty]

So the CPU you have has 16 PCIe lanes of its own that are dedicated to the top two PCIe x16 slots.

Then there is the chipset, the Z390, which has 24 additional PCIe lanes to use which are normally split up into the NVMe drives, USB ports and other PCIe slots. They are not affected by PCIe x16 1 or 2 so your 2080Ti is only using the 16 slots from your CPU itself. So in total (if you include the DMI 3.0 link between the CPU and chipset) your system has 44 PCIe lanes.

The NVMe drives are using 8 (each one is x4) of the additional 24 PCIe lanes which leaves 16 of those minus whatever other devices they may be distributed to.

In short, your friend is wrong and you can put the 10Gb card into either of the x4 slots and it will work as your system has plenty of PCIe lanes left.

 

[cassidydotdk]

It DID seem rather odd to me, so this is excellent news This will be my project for tomorrow.

Thanks a lot