Confused about CPU PCIe

[BillyDoz]

I'm a little confused about PCIe. I have an Intel 6800k that only has 28 PCIe lanes. I'm using it on an MSI x99a gaming pro carbon. I'm also using 2x8 Gskill 2400 DDr4 ram. If I try to run SLI with 2 GTX 1080's, and also use an M.2 port will my performance be limited due to only 28 lanes? And the CPU says it only has 4 memory channels. Does that mean that I can't use all the memory ports that are on my motherboard? Any help would be appreciated

[Electronics Wizardy]

gpu's can run at 8x with no performance cut. You will be fine.

 

You have 2 sticks per channel, so 8 sticks.

[PCGuy_5960]

2 minutes ago, BillyDoz said:

And the CPU says it only has 4 memory channels. Does that mean that I can't use all the memory ports that are on my motherboard?

The motherboard has 8 slots, 2 slots per channel. so you can use all of them

[Mira Yurizaki]

The CPU will split up the PCIe lane usage to x8 for the two GPUs and x4 for the M.2 NVMe SSD. And there's no real performance loss going to x8: https://www.techpowerup.com/reviews/NVIDIA/GeForce_GTX_1080_PCI_Express_Scaling/

[stealth80]

Your chipset also has PCI lanes

 

 

[PCGuy_5960]

1 minute ago, stealth80 said:

Your chipset also has PCI lanes

Only 8, and they are PCIE 2.0. So they are not really usable for M.2 SSDs or SLI....

[Energycore]

Just now, PCGuy_5960 said:

Only 8, and they are PCIE 2.0. So they are not really usable for M.2 SSDs or SLI....

Unless you have the most expensive NVMe drive, you won't be bottlenecked by PCI-E 2.0 x4 lanes (which can do up to 2GB/s). For SLI it's a bit low but for an M.2 SSD you'll hardly feel the difference between 2.0 x4 and 3.0 x4

[stealth80]

1 minute ago, PCGuy_5960 said:

Only 8, and they are PCIE 2.0. So they are not really usable for M.2 SSDs or SLI....

my point is that things like SSD, audio etc will supplied from the X99 chipset, leaving the CPU to deal with SLI and M.2

[PCGuy_5960]

Just now, Energycore said:

Unless you have the most expensive NVMe drive, you won't be bottlenecked by PCI-E 2.0 x4 lanes (which can do up to 2GB/s). For SLI it's a bit low but for an M.2 SSD you'll hardly feel the difference between 2.0 x4 and 3.0 x4

AFAIK, those lanes can't be used for M.2 SSDs...

[Energycore]

Just now, PCGuy_5960 said:

AFAIK, those lanes can't be used for M.2 SSDs...

According to whom? I don't see a reason why they can't be used for M.2 SSDs

[PCGuy_5960]

Just now, Energycore said:

According to whom? I don't see a reason why they can't be used for M.2 SSDs

Don't NVMe SSDs use PCIe 3.0?

[stealth80]

2 minutes ago, PCGuy_5960 said:

AFAIK, those lanes can't be used for M.2 SSDs...

 

1 minute ago, Energycore said:

According to whom? I don't see a reason why they can't be used for M.2 SSDs

They can, but only via add in card like a normal PCIE device (and only if the bios allows that assignment for a boot device), much like I once used on my current build to get max m.2 speeds as the Ranger 7 is only PCIE 2.0 x2

[stealth80]

Just now, PCGuy_5960 said:

Don't NVMe SSDs use PCIe 3.0?

They can be used in PCIE 2.0 also, just limited by data transfer speeds

 

[Energycore]

10 minutes ago, BillyDoz said:

I'm a little confused about PCIe. I have an Intel 6800k that only has 28 PCIe lanes. I'm using it on an MSI x99a gaming pro carbon. I'm also using 2x8 Gskill 2400 DDr4 ram. If I try to run SLI with 2 GTX 1080's, and also use an M.2 port will my performance be limited due to only 28 lanes? And the CPU says it only has 4 memory channels. Does that mean that I can't use all the memory ports that are on my motherboard? Any help would be appreciated

As for RAM and PCI-E lanes, they're independent and you can run any number of RAM sticks without using up any PCI-E bandwidth. You can run 2 1080s on x8/x8 and use the other 12 lanes for M.2 SSDs or alikes. Your performance will not be limited at all.

Just now, PCGuy_5960 said:

Don't NVMe SSDs use PCIe 3.0?

PCI-E revisions are forwards and backwards compatible. You can use a GTX 1080 on a 2009 motherboard with PCI-E 1.0 (why you'd do it is a different matter entirely)

[PCGuy_5960]

Just now, Energycore said:

PCI-E revisions are forwards and backwards compatible. You can use a GTX 1080 on a 2009 motherboard with PCI-E 1.0 (why you'd do it is a different matter entirely)

I know, I simply thought that M.2 SSDs require PCIe 3.0...

[AnonymousGuy]

2 minutes ago, Energycore said:

. You can use a GTX 1080 on a 2009 motherboard with PCI-E 1.0 (why you'd do it is a different matter entirely)

You can even go so far as to adapt PCIe x 1 to PCI and it's compatible down to PCI rev 2.1 or something like that.  PCIe is one of few things where "it just works" in terms of compatibility, so long as you don't get fucked over by lane assignment gremlins ("this slot becomes disabled if....").

[BillyDoz]

1 hour ago, Energycore said:

As for RAM and PCI-E lanes, they're independent and you can run any number of RAM sticks without using up any PCI-E bandwidth. You can run 2 1080s on x8/x8 and use the other 12 lanes for M.2 SSDs or alikes. Your performance will not be limited at all.

PCI-E revisions are forwards and backwards compatible. You can use a GTX 1080 on a 2009 motherboard with PCI-E 1.0 (why you'd do it is a different matter entirely)

Thanks for the help!