PCIe 3.0/2.0 x16 single at x16, dual at x8/x8 i am confused

[Typherian]

Hello and first of all my apologies if this is something that is cover in a previous topic but i am really confused with pcie expansion slots and sli cards. I was thinking of upgrading to a new gpu but the prices have skyrocketed with all the cryptocurrency farmers so i was thinking of adding a second gpu instead. My system uses an asus z97 pro gamer https://www.asus.com/us/Motherboards/Z97PRO_GAMER/overview/ motherboard and i i am currently using an asus gtx 970 https://www.asus.com/us/Graphics-Cards/STRIXGTX970DC2OC4GD5/. I have found exactly the same card to use but i dont understand how the expansion slots are working (Single at x16, dual at x8/x8, ) does that mean that the adding a second card will cut it's performance in half? or that the gpu can work at full speed at both x16 and x8?

[NelizMastr]

Your CPU has 16 PCIe lanes to distribute, so to accommodate two cards, both slots will run at 8x speed.

 

Mind you, 8 lanes of PCIe 3.0 have plenty of bandwidth for a modern graphics card, even for a Titan V  

[Lurick]

It means adding a second card will have both PCIe slots operate at x8 and x8 both but it will not impact performance. A GTX 1080Ti could operate at PCIe 3.0 x4 mode with minimal impact to performance.

[deXxterlab97]

[Typherian]

Wow that was quick thanks guys, it finally made some sense as far as theory goes but right now i noticed that not all the slots are the same on the mobo, some have pins all the way while some have half way, my gpu is now seated at the grey slot (1) where is the second card supposed to go?

[deXxterlab97]

3 minutes ago, Typherian said:

Wow that was quick thanks guys, it finally made some sense as far as theory goes but right now i noticed that not all the slots are the same on the mobo, some have pins all the way while some have half way, my gpu is now seated at the grey slot (1) where is the second card supposed to go?

 

Usually the card will be seated at slot 1 and 3. You should read motherboard manual as to which slot supports SLI

[Oshino Shinobu]

3 minutes ago, Typherian said:

Wow that was quick thanks guys, it finally made some sense as far as theory goes but right now i noticed that not all the slots are the same on the mobo, some have pins all the way while some have half way, my gpu is now seated at the grey slot (1) where is the second card supposed to go?

 

From top to bottom, the slots on your board:

 

PCIe 1x

PCIe 16x

PCI

PCIe 1x

PCIe 16x

PCI

PCIe 16x

 

The PCI slots are an older standard and are not backwards compatible with PCIe (though you can get adaptors). If you look at the notches, they're in different places, so you can't plug PCIe devices into PCI slots or PCI devices into PCIe slots.

 

You will want one of the cards in the first PCIe 16x slot, and you should be able to have the other one in either of the PCIe 16x slots below it. The most common way would be to have it in the one closest to it (the slot labelled 3 in your image)

[Typherian]

So the gray slot is physical x16 and wired x16 and the slots 3 and 5 are physical x16 but wired for x8, ok now i understand! Thank you guys for your replies they were all very helpful.

 

[Oshino Shinobu]

2 minutes ago, Typherian said:

So the gray slot is physical x16 and wired x16 and the slots 3 and 5 are physical x16 but wired for x8, ok now i understand! Thank you guys for your replies they were all very helpful.

 

Not quite. Upon looking at the motherboard's specs, it seems like it's like this:

 

Top, grey PCIe slot is PCIe 3.0 16x and the first black 16x slot is the same. Both are wired for 16x but will run at 8x if both are occupied. The bottom 16x slot is a 2.0 16x slot, but can only run at 4x max. 

 

From motherboard's specs:

 

Quote

2 x PCIe 3.0/2.0 x16 (Single at x16, dual at x8/x8, ) 
1 x PCIe 2.0 x16 (max at x4 mode, black) 
2 x PCIe x1 
2 x PCI

 

[Thermosman]

40 minutes ago, NelizMastr said:

Your CPU has 16 PCIe lanes to distribute, so to accommodate two cards, both slots will run at 8x speed.

 

Mind you, 8 lanes of PCIe 3.0 have plenty of bandwidth for a modern graphics card, even for a Titan V  

actually its not