I have a question about PCIE lanes and how many can I use etc

[BOBGEN]

So Basically I have a ryzen 5 2600 (I know not great I am going to upgrade soon), A ASUS ROG STRIX X570-F and a GTX 1660 Super. I was wondering how PCIE lanes work?

I have one graphics card and I have heard that uses 16 lanes, I have also heard my CPU supplies 20 lanes. First is that correct?

Secondly I was wondering how SATA and M.2 drives work, I thought that uses lanes as well but I have 5 Sata devices and one M.2 currently connected.

And third I was thinking about getting another lesser graphics card so I can run more monitors as I currently have 3 but want more. If I added another card would that use more lanes than I have? Would it just not work or would it make both cards work less efficiently

One more question If I add something else to the PCIE ports like a Wifi card or a sata adaptor will that use more lanes as well?

 

Basically I have no idea about any of this and it is likely I have asked a stupid question.

Thanks for your help and time

[Spotty]

2 minutes ago, BOBGEN said:

So Basically I have a ryzen 5 2600 (I know not great I am going to upgrade soon)

The Ryzen 2600 is pretty decent. Very good for its price.

 

2 minutes ago, BOBGEN said:

I have one graphics card and I have heard that uses 16 lanes, I have also heard my CPU supplies 20 lanes. First is that correct?

Correct. 16 goes to the PCIe slots, 4 for PCIe SSD. You also have 4 that goes to the motherboard chipset.

 

4 minutes ago, BOBGEN said:

Secondly I was wondering how SATA and M.2 drives work, I thought that uses lanes as well but I have 5 Sata devices and one M.2 currently connected.

SATA drives communicate to the chipset.

 

5 minutes ago, BOBGEN said:

And third I was thinking about getting another lesser graphics card so I can run more monitors as I currently have 3 but want more. If I added another card would that use more lanes than I have? Would it just not work or would it make both cards work less efficiently

It splits the x16. The two cards will run at x8 each. Unless you have an RTX3090 you won't see any performance loss running the cards at x8.

 

6 minutes ago, BOBGEN said:

One more question If I add something else to the PCIE ports like a Wifi card or a sata adaptor will that use more lanes as well?

The x1 slots and the bottom x16 length slot communicate to the chipset. Won't interfere with the graphics cards (unless for some reason you put a wifi card in the top x16 slot and your graphics card in the bottom x16 slot that goes to the chipset)

 

You can check your motherboard manual for more details. Manuals often have a block diagram showing the PCIe lane configuration or a table showing what runs at what speed and what configurations can be used.

[BOBGEN]

Thanks for the reply, Very helpful.

I just have a few more questions

16 minutes ago, Spotty said:

16 goes to the PCIe slots, 4 for PCIe SSD. You also have 4 that goes to the motherboard chipset.

How does this work? it adds up to 24 and my CPU only has 20 Pcie.

 

17 minutes ago, Spotty said:

The x1 slots and the bottom x16 length slot communicate to the chipset

So because these communicate to the chipset what would happen if I installed a GPU into the bottom x16?

[Stahlmann]

30 minutes ago, Spotty said:

It splits the x16. The two cards will run at x8 each. Unless you have an RTX3090 you won't see any performance loss running the cards at x8.

This depends heavily on the game. Even with lower-end GPUs there CAN be a noticeable performance loss.

[mariushm]

18 minutes ago, BOBGEN said:

Thanks for the reply, Very helpful.

I just have a few more questions

How does this work? it adds up to 24 and my CPU only has 20 Pcie.

 

So because these communicate to the chipset what would happen if I installed a GPU into the bottom x16?

The CPU has 24 pci-e lanes.  It only advertises 20, because 4 pci-e lanes are permanently used to connect the chipset to the CPU. 

The remaining 20 can be assigned for various things. Almost always the first 16 are assigned to the first pci-e x16 slot, and the remaining 4 are assigned to the first m.2 connector.

 

There is at least one motherboard which takes those 16 and connects them to a pci-e x16 slot and TWO m.2 connectors, and a THIRD m.2 connector connected to the other 4 pci-e lanes.  It automatically converts the pci-e x16 slot to pci-e x8, when you insert a M.2 SSD in those two M.2 connectors. 

 

The chipset creates 6 or 8 pci-e lanes, depending on the chipset model. 

Some lanes go to the pci-e x1 slot, usually 4 go to the bottom pci-e x16 slot.  While the slot is physically shaped like pci-e x16, there are only 4 pci-e lanes in it. 

On some motherboards, if you install a nvme SSD in a 2nd or 3rd M.2 connector, the chipset has to "borrow" pci-e lanes from pci-e x1 or that bottom pci-e x16 slot, and give them to that 2nd or 3rd M.2 connector to make it working.  In such case, the pci-e x1 slot becomes unusable, or the pci-e x16 slot becomes x2 or x1 instead of x4 electrically. 

 

If you install a video card in the pci-e x16 slot at the bottom, it will work just fine, but now all the data goes between chipset, instead of going directly between video card and the cpu. Also, the slot has only 4 pci-e lanes, and the chipset also has only 4 pci-e lanes worth of bandwidth with the cpu, so the performance of the video card is gonna be a bit lower... think of it like instead of 100 fps, you may get 85-90 fps in games. 

 

Another thing to note is that nVidia insists on having at least 8 pci-e lanes on each video card to establish SLI between two cards. As the bottom slot is physically x16, but electrically only pci-e x4 on most AM4 motherboards, SLI would not work if you insert a video card in that bottom slot. 

The motherboard would also need to have SLI license from nVidia, and such board would not have one in the first place... if the board doesn't advertise SLI, SLI most likely won't work.

[Drama Lama]

28 minutes ago, BOBGEN said:

How does this work? it adds up to 24 and my CPU only has 20 Pcie.

You have 20 „ usable „ PCIe lanes 

so 20 lanes that can be used for GPUs , WiFi or network cards and other expansion cards

the remaining 4 lanes are connected to the chipset, wich handles usb and sata connectors

[ThePinkPiggy]

I have a similar question but regarding the Intel side. I noticed that most Intel 10th gen processors (10400, 10600K, 10700K, 10900K) support only 16 PCIe lanes (as per the Intel product page). If the GPU in the PCIe x16 slot uses 16 lanes, and the M.2 connector in PCIe x4 mode uses 4 lanes, does this mean that on an Intel platform the GPU will only run in x8 mode if a M.2 NVME SSD is connected to the M.2 PCIe x4 slot?

[mariushm]

No, on Intel all the pci-e lanes besides the 16 cpu ones come from the chipset ... so the M.2 lanes come from chipset. 

The 16 lanes go to the pci-e x16, or the first two pci-e x16 slots (split into 2 x8 slots if two cards are inserted)