PCI-e lanes and card setup

[tomaatvk]

Today I got a really good deal on the mushkin scorion deluxe (PCI-e 8x 2.0 SSD) so I orderd it directly. However, looking at my motherboard (the asrock Z77 extreme 4) there might be 2 small problems.

 

1. My GTX 970 needs at least 8 PCI-e lanes and the SSD also 8 (or will it get converted to 4 because 8x 2.0 is as fast as 4x 3.0?) with my soundcard also pulling one PCI-e 1x 2.0 lane. This totals out at 17 PCI-e lanes but the CPU can only do 16 lanes. Will my motherboard chipset do the 17th lane as that is included in the block diagram of IVY bridge?

 

2. Because of the limited ammount of slots on my motherboard I can only configure my expansion cards in 2 ways. I have a tripple slot GTX 970 on PCI-e 16x 3.0 (will work on 16x, 8x, 3.0 and 2.0 PCI-e lanes), a sound card on PCI-e 1x 2.0, a wifi card on regular PCI and the SSD on PCI-e 8x 2.0. Below you can see a scematic of how I can lay the cards out.

Spoiler

To do the yellow config I will have to turn my CPU cooler to make it fit.

On general the yellow config will give me slightly better GPU airflow (as in the red config the SSD will block 1.5 of the 3 GPU fans) but it will look uglier and cost me a bit of thermal compound.

Also, I'm not sure if my GPU will work if it's in the 2nd PCI-e 16x slot because it's not the primairy one.

 

My case is made out of k'nex and has a test bench setup so I have no case restrictions (no panel at the bottom blocking airflow, no lenth restrictions or whatever).

 

Thank you if you can be of any help or have any suggestions.

[Glenwing]

Today I got a really good deal on the mushkin scorion deluxe (PCI-e 8x 2.0 SSD) so I orderd it directly. However, looking at my motherboard (the asrock Z77 extreme 4) there might be 2 small problems.

 

1. My GTX 970 needs at least 8 PCI-e lanes and the SSD also 8 (or will it get converted to 4 because 8x 2.0 is as fast as 4x 3.0?) with my soundcard also pulling one PCI-e 1x 2.0 lane. This totals out at 17 PCI-e lanes but the CPU can only do 16 lanes. Will my motherboard chipset do the 17th lane as that is included in the block diagram of IVY bridge?

 

2. Because of the limited ammount of slots on my motherboard I can only configure my expansion cards in 2 ways. I have a tripple slot GTX 970 on PCI-e 16x 3.0 (will work on 16x, 8x, 3.0 and 2.0 PCI-e lanes), a sound card on PCI-e 1x 2.0, a wifi card on regular PCI and the SSD on PCI-e 8x 2.0. Below you can see a scematic of how I can lay the cards out.

Spoiler

To do the yellow config I will have to turn my CPU cooler to make it fit.

On general the yellow config will give me slightly better GPU airflow (as in the red config the SSD will block 1.5 of the 3 GPU fans) but it will look uglier and cost me a bit of thermal compound.

Also, I'm not sure if my GPU will work if it's in the 2nd PCI-e 16x slot because it's not the primairy one.

 

My case is made out of k'nex and has a test bench setup so I have no case restrictions (no panel at the bottom blocking airflow, no lenth restrictions or whatever).

 

Thank you if you can be of any help or have any suggestions.

 

Graphics cards can work fine with 4 lanes, you don't need 8, and PCIe 3.0 x4 is unlikely to really affect your performance.

 

The 1x slots are wired to the chipset, so as long as your soundcard is fitted in an x1 slot it won't use any of the CPU's lanes.

[tomaatvk]

Graphics cards can work fine with 4 lanes, you don't need 8, and PCIe 3.0 x4 is unlikely to really affect your performance.

 

The 1x slots are wired to the chipset, so as long as your soundcard is fitted in an x1 slot it won't use any of the CPU's lanes.

 

Thank you for the help, I just thought I heard somewhere that nVidia implemented a minimum of 8x to run it at all but it could just be my brains derping out.

 

Any idea of which card layout I should go with?

[NumLock21]

The physical x1 slots takes lanes from your chipset not from the cpu. The x16 slot takes lanes from the cpu and your boards supports SLI, which means both x16 slots can run at x8 mode. When that PCIe SSD is installed into the 2nd x16 slot, your gpu runs at x8 and your PCIe SSD also runs at x8.

The x8 for Nvidia is required to run SLI because they will not allow it to work at x4.

[Glenwing]

Thank you for the help, I just thought I heard somewhere that nVidia implemented a minimum of 8x to run it at all but it could just be my brains derping out.

 

Any idea of which card layout I should go with?

Yeah that's not true at all, but it's a commonly held myth that people keep repeating. There is a rule where if you use multiple NVIDIA graphics cards in SLI, they must be at ×8/×8 (of any PCIe version) or above, but somehow that has turned into everyone thinking all graphics cards from both companies need ×8 to work at all, and ×8 Gen3 or equivalent (×16 Gen2) to work in multi-GPU.

For clarity:

- There are no lane restrictions for graphics cards. You can use any graphics card at ×1 if you really wanted to. I have run Gen2 ×1 before with my 780 Ti. Surprisingly, still playable framerates.

- The ×8/×8 lane restrictions in SLI are only for NVIDIA SLI. AMD cards can run in ×1/×1 Crossfire if you really wanted to, though the framerates won't be great Even Gen 3 ×4/×4 would be adequate though.

- The ×8/×8 lane restriction in NVIDIA SLI does not mean "×8 Gen3 or equivalent", it just means ×8. It is independent of PCIe version. ×8/×8 in Gen1/Gen2/Gen3 all works for SLI. ×4/×4 in Gen1/Gen2/Gen3 does not work for SLI.

So, if anyone tells you "graphics cards need ×8" just point them here

For your configuration, the slots don't really matter, the main PCIe lanes will be split ×8/×8 between the GPU and SSD. As long as you plug your sound card into a dedicated ×1 slot there shouldn't be any issues.

[tomaatvk]

The physical x1 slots takes lanes from your chipset not from the cpu. The x16 slot takes lanes from the cpu and your boards supports SLI, which means both x16 slots can run at x8 mode. When that PCIe SSD is installed into the 2nd x16 slot, your gpu runs at x8 and your PCIe SSD also runs at x8.

The x8 for Nvidia is required to run SLI because they will not allow it to work at x4.

 

Thanks for the clarification. One less thing to worry about.

[tomaatvk]

-snip-

 

Is it me or doesn't that make any sense, why would gen 1 8x be enough while gen 3 4x (which has double the speed) not be enough or is that just because of reasons that don't make any sense?

[Glenwing]

Is it me or doesn't that make any sense, why would gen 1 8x be enough while gen 3 4x (which has double the speed) not be enough or is that just because of reasons that don't make any sense?

 

You're right, Gen3 ×4 has higher bandwidth than Gen1 ×8. The reason Gen1 ×8 works is because the restriction isn't for any technical reason, it's not about bandwidth. It's a completely arbitrary restriction that's just there because NVIDIA says so.

[TomvanWijnen]

I see you've been helped already But yes, you should be able to run your 970 in the second slot. I've also run mulitple GPUs (non SLI/CFX), and it has worked fine. (we own the same motherboard and GPU)

 

You're right, Gen3 ×4 has higher bandwidth than Gen1 ×8. The reason Gen1 ×8 works is because the restriction isn't for any technical reason, it's not about bandwidth. It's a completely arbitrary restriction that's just there because NVIDIA says so.

Sorry, but LOL  :lol:  :lol:  :lol: