Question What's the use of a 2nd PCI-E x16 slot ?

[eziowar]

Hi, i see many mobos have two PCI-E x16 slots, where the primary PCI-E x16 is for my gpu, but 2nd one only supports up to x4 or something. I'll never use more than 1 gpu on my mobo. then what's the use of a 2nd PCI-E x16?

 

[Colif]

i guess it is for people who do use 2 GPU in their systems. You can still get some single slot cards, but finding one that supports SLI or AMD's version would be a fun search

If the card isn't as big as mine, you could maybe put a WIFI card in there if its not already on motherboard. There are uses for pcie slots besides Graphics cards. Some people use them for additional nvme.

My gpu is 3.5 slots so I can't even see the 2nd slot under the GPU. its chunky

i thought I had a photo showing what little I can see under card, but it might have been the previous card - seems it was and you can't even see it under it

I can almost see as much still but really all my other pci slots are useless.

miners have been known to have up to 6 cards on a board... not all motherboards are used for gaming.

Soundcards also use pcie connections.

 

[eziowar]

i guess it is for people who do use 2 GPU in their systems. You can still get some single slot cards, but finding one that supports SLI or AMD's version would be a fun search

If the card isn't as big as mine, you could maybe put a WIFI card in there if its not already on motherboard. There are uses for pcie slots besides Graphics cards. Some people use them for additional nvme.

My gpu is 3.5 slots so I can't even see the 2nd slot under the GPU.

miners have been known to have up to 6 cards on a board... not all motherboards are used for gaming.

Soundcards also use pcie connections.

but the pcie connectors on wifi adapter or capture cards way smaller than a X16 pcie slot, how those do fit into X16 slot, i thought they only fit into X1 pcie slot?

 

[bill001g]

but the pcie connectors on wifi adapter or capture cards way smaller than a X16 pcie slot, how those do fit into X16 slot, i thought they only fit into X1 pcie slot?

Nope pcie slots are designed so the pins of the shorter cards match up with the pins on the front end of a longer slot. It is a interesting design that allows this. Pretty much if the card fits in the slot it will work.

Partially I think they have multiple 16x slots for people that have restrictions on which slot they use. Maybe some card has some big water cooler on it or something on the case prevent use of a particular slot.

You do see people talking about using the 16x pcie slots for SSD type storage adapter cards. There are still restrictions on how many actual pcie lanes the cpu has so just adding more slots does not increase that.

 

[Colif]

reason second slot runs at x4 is its running off motherboard, not CPU.

if the card fits it should work. Some cards are designed for specific slots. It will only run at 1x anyway.

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above only really works on thread ripper systems as they have enough spare pcie lanes to control more nvme this way.

 

[Eximo]

I would say in consumer PCs the most common installation would be additional M.2 slots, Very fast Wireless and Ethernet NICs, maybe a SATA or SAS controller for additional hard drives. A lot of people use video capture cards for streaming.

Some boards support installing thunderbolt cards. You can add extra fast USB ports if you have a need for more than one or two.

 

[CountMike]

There are a lot of PCIe cards for different functions and except for some (not all GPUs) they don't or can't use all 16 PCIe lanes, ranging mostly from x1 to x4 or x8 tops.
Some or most have first x16 and first M.2 NVME using PCIe lanes from CPU which in consumer CPUs have 24 lanes with 4 reserved for internal PCIe devices. Other PCIe lanes are connected to chipset and number varies with MB's rating. More expensive ones have better chipset and with it more functions.