What does PCI x16 and x8 mean? It is a unit of speed, or is it a measure of physical size?

[Likespieman007]

Hey guys, I just have a quick question.
According to the internet, x16 and x8 are just pcie slot lengths. Like the Pcie 3.0 would be the long slot which would be called x16. However, I heard some say that x16 and x8 are different slot speeds as well.

When your motherboard manual is referring to the two x16 slots on your motherboard, are they referring to speed or size?

Im really confused, cant seem to find good info anywhere else 😛

 

[dudio]

Everything you need to know:

http://www.hardwaresecrets.com/everything-you-need-to-know-about-the-pci-express/

 

[photonboy]

Hey,
x16 is the size
x8 can be the size, but often is a x16 slot running in x8 mode that is being discussed.

It's worth noting that it's pretty hard to find a graphics card that will need more than x8 PCIe v3 bandwidth.

I prefer Wikipedia: https://en.wikipedia.org/wiki/PCI_Express

 

[photonboy]

You may find this useful, but again if this is a question about bandwidth then as long as you have at least "x8" electrically for two slots for PCIe v3 then there is no bandwidth issue.

So it's going to be "x16" physically, with possibly both the top x16 slots running in x8 mode once you add two video cards (because there is only a limited amount of PCIe bandwidth that can be used at any one time).

http://www.tomshardware.com/reviews/amd-crossfire-nvidia-sli-multi-gpu,2678-5.html

(it's from 2010 and probably using PCIe v2 but it still applies to modern PCIe v3 setups)

 

[Likespieman007]

You may find this useful, but again if this is a question about bandwidth then as long as you have at least "x8" electrically for two slots for PCIe v3 then there is no bandwidth issue.

So it's going to be "x16" physically, with possibly both the top x16 slots running in x8 mode once you add two video cards (because there is only a limited amount of PCIe bandwidth that can be used at any one time).

http://www.tomshardware.com/reviews/amd-crossfire-nvidia-sli-multi-gpu,2678-5.html

(it's from 2010 and probably using PCIe v2 but it still applies to modern PCIe v3 setups)

Thanks for the reply, I fully understand how this works now!

 

[Likespieman007]

You may find this useful, but again if this is a question about bandwidth then as long as you have at least "x8" electrically for two slots for PCIe v3 then there is no bandwidth issue.

So it's going to be "x16" physically, with possibly both the top x16 slots running in x8 mode once you add two video cards (because there is only a limited amount of PCIe bandwidth that can be used at any one time).

http://www.tomshardware.com/reviews/amd-crossfire-nvidia-sli-multi-gpu,2678-5.html

(it's from 2010 and probably using PCIe v2 but it still applies to modern PCIe v3 setups)

For my msi sli z97s krait edition motherboard, if it says that it has two pcie x16 3.0 slots, and in the bios it says one of the slots is running at x8, that means that the physical size is x16 but it runs at x8 right?