How are pcie lanes distributed?

[EmoChipmonk]

So I plan on getting a 3080ti and a 4900x (I think), 4 ext bus usb card and using a 3x4 m.2 nvme drive assuming I left the video card at 16 lanes what would happen to the drive and the usb card that uses 4 lanes I think?

 

I also wanted to get al legate capture card and mabey a sound card at one point.

[3rrant]

3 minutes ago, EmoChipmonk said:

So I plan on getting a 3080ti and a 4900x (I think), 4 ext bus usb card and using a 3x4 m.2 nvme drive assuming I left the video card at 16 lanes what would happen to the drive and the usb card that uses 4 lanes I think?

 

I also wanted to get al legate capture card and mabey a sound card at one point.

There's no 4900x or 4th gen Ryzen announcement what so ever, how could you know how many lanes they have? You can assume they have the same lanes of 3xxx series but that's nothing real. Plus, it also depends on the motherboard you choose. They are not all configured the same way.

 

Generally speaking, the GPU gets the full 16 lanes and the drivers share some lanes because you're never gonna use them at full speed contemporarily anyway. Other addon card like usb or audio are unlikely to even saturate a 1x speed link.

[EmoChipmonk]

14 minutes ago, 3rrant said:

There's no 4900x or 4th gen Ryzen announcement what so ever, how could you know how many lanes they have? You can assume they have the same lanes of 3xxx series but that's nothing real. Plus, it also depends on the motherboard you choose. They are not all configured the same way.

 

Generally speaking, the GPU gets the full 16 lanes and the drivers share some lanes because you're never gonna use them at full speed contemporarily anyway. Other addon card like usb or audio are unlikely to even saturate a 1x speed link.

So other devices would just piggy back off the video cards lanes? Well vr takes up alot of bandwidth which is why the card will be there.

[3rrant]

1 minute ago, EmoChipmonk said:

So other devices would just piggy back off the video cards lanes? Well vr takes up alot of bandwidth which is why the card will be there.

I'm not sure I understood this correctly but:

• It depends on the motherboard. However, the first (top-most) PCI-E slot is considered "GPU-reserved" by all manifacturers. This slot always has access to 16 lanes of 3.0/4.0 gen speed depending on the CPU installed.
• If you have two videocards installed, the system splits these 16 lanes into 2x8.

Taking the X570 platform with a 3950X as an example, the CPU has 24 PCI-E 4.0 direct lanes usable. 4 of these go to the chipset. 4 goes directly to a NVMe drive if present and 16 goes to graphics (in 1x16 or 2x8 config).

 

Motherboard makes then can ADD extra PCI-E 4.0 support which are not directly under the CPU control. So if you want three SEPARATE NVMe drives with 4x4.0 speed, you need to search for a motherboard with that feature (and it will cost a lot). Otherwise, you're gonna end up with 1 ssd at 4x4.0 speed and the others under the chipset, so equivalent to 8x3.0 speed or something like that. Other addon cards will fall under the chipset as well, but they are not bandwidth intensive so they should have no problem.

 

I really cannot foresee the need for such massive storage solution being all used at once.. so I don't think that's the way to go. Get a bigger SSD on the 4x4.0 direct lane and don't worry about anything else.

 

Of course, if 4xxx series increase the lanes avaiable... that will possibly resolve your issue but I don't think they will. If they have lanes to spare they are gonna limit them to TR platforms.

[EmoChipmonk]

7 minutes ago, 3rrant said:

I'm not sure I understood this correctly but:

• It depends on the motherboard. However, the first (top-most) PCI-E slot is considered "GPU-reserved" by all manifacturers. This slot always has access to 16 lanes of 3.0/4.0 gen speed depending on the CPU installed.
• If you have two videocards installed, the system splits these 16 lanes into 2x8.

Taking the X570 platform with a 3950X as an example, the CPU has 24 PCI-E 4.0 direct lanes usable. 4 of these go to the chipset. 4 goes directly to a NVMe drive if present and 16 goes to graphics (in 1x16 or 2x8 config).

 

Motherboard makes then can ADD extra PCI-E 4.0 support which are not directly under the CPU control. So if you want three SEPARATE NVMe drives with 4x4.0 speed, you need to search for a motherboard with that feature (and it will cost a lot). Otherwise, you're gonna end up with 1 ssd at 4x4.0 speed and the others under the chipset, so equivalent to 8x3.0 speed or something like that. Other addon cards will fall under the chipset as well, but they are not bandwidth intensive so they should have no problem.

 

I really cannot foresee the need for such massive storage solution being all used at once.. so I don't think that's the way to go. Get a bigger SSD on the 4x4.0 direct lane and don't worry about anything else.

 

Of course, if 4xxx series increase the lanes avaiable... that will possibly resolve your issue but I don't think they will. If they have lanes to spare they are gonna limit them to TR platforms.

It was the add in cards I was worried about. 3x4 nvme is the type of ssd. I'm not using 3 of them

[3rrant]

1 minute ago, EmoChipmonk said:

It was the add in cards I was worried about. 3x4 nvme is the type of ssd. I'm not using 3 of them

OH you meant PCI-E 3.0 at x4 speed? Then you're good to go and no need to worry about anything! I thought 3 ssds at PCI-E 4.0 full speed.

[EmoChipmonk]

Just now, 3rrant said:

OH you meant PCI-E 3.0 at x4 speed? Then you're good to go and no need to worry about anything! I thought 3 ssds at PCI-E 4.0 full speed.

I wish. That would be great.