Question CPU 16 PCIe Lanes configuration.

[Endre]

Hello!
My CPU is i7-9700K and it has a maximum of 16 PCIe lanes.
I have a videocard that’s PCIe 3.0 x16.
I’d like to upgrade my PC adding the Samsung 970 Pro 1TB SSD, that uses PCIe 3.0 x4.
My question is this: If my PCIe lanes are only 16, adding the SSD will reduce my video card’s lanes to 12?

 

[Eximo]

The CPU has 16x lanes dedicated to usually one 16x graphics slot with the capability to split out to 2x8 slots and on some boards 8x, and two 4x slots.

The motherboard chipset has its own PCIe lanes that it can distribute.

See this diagram:

https://hothardware.com/ContentImages/Article/2792/content/small_z390-diagram.png

 

[Endre]

The CPU has 16x lanes dedicated to usually one 16x graphics slot with the capability to split out to 2x8 slots and on some boards 8x, and two 4x slots.

The motherboard chipset has its own PCIe lanes that it can distribute.

See this diagram:

https://hothardware.com/ContentImages/Article/2792/content/small_z390-diagram.png

Alright! So what it means is that the graphics card will use the x16 PCIe lanes assigned by the CPU, and the SSD will use x4 PCIe lanes out of x24 PCIe lanes assigned by the motherboard.
No sharing of bandwidth in this type of configuration at all!
(Please correct me if I’m wrong).

 

[Eximo]

In simple terms yes, that is correct.

DMI is still using the PCIe bus as I recall, but those are dedicated lines to the chipset. Essentially 4x PCIe between the chipset and the CPU.

 

[Endre]

In simple terms yes, that is correct.

DMI is still using the PCIe bus as I recall, but those are dedicated lines to the chipset. Essentially 4x PCIe between the chipset and the CPU.

Alright! So, by what I understand, using one M.2 NVMe PCIe 3.0 x4 will work at its full speed, but if I install 3 SSDs like that and configure them in RAID-0, I’ll see no benefit at all, because of the x4 connection limit between the CPU and the Chipset.

 

[Eximo]

Again, yes and no. Depends on the bandwidth the SSDs can consume. I don't think there are all that many that will go for a full 4GB/s second.

You would need to be dealing with enormous data transfers on a regular basis to justify such a thing. And at that point it makes more sense to get a dedicated controller and slap it in a PCIe x16 slot.