skylake Z170 Motherboard 3rd PCIe SLOT

[SmashinMachine]

HI,

I know that most of z170 boards last Pcie-SLot are connected to PCH. But how can these Motherboards achieve the 3-way Crossfire? It means that 3rd SLOT connects to the CPU????

How does it work????

Is the 3rd Slot capable to run a single GPU?

For example ASUS Z170-A Motherboard: It supports 3-way AMD crossfireX 

Here is the PCI-e Routing Diagramm

[Jumper118]

1 minute ago, SmashinMachine said:

HI,

I know that most of z170 boards last Pcie-SLot are connected to PCH. But how can these Motherboards achieve the 3-way Crossfire? It means that 3rd SLOT connects to the CPU????

How does it work????

Is the 3rd Slot capable to run a single GPU?

For example ASUS Z170-A Motherboard: It supports 3-way AMD crossfireX 

Here is the PCI-e Routing Diagramm

 

 

it will run x8 x4 x4 when 3 way cf

[SmashinMachine]

Just now, Jumper118 said:

it will run x8 x4 x4 when 3 way cf

Yes, I know that but you missunderstand my question...

The third Slot does NOT use the CPU Lanes, it uses the PCH lanes. How can these SLOT  use the Lanes from CPU???

[Jumper118]

8 minutes ago, SmashinMachine said:

Yes, I know that but you missunderstand my question...

The third Slot does NOT use the CPU Lanes, it uses the PCH lanes. How can these SLOT  use the Lanes from CPU???

its does use the cpu lanes. the diagram is wrong or it cant do 3 way cf  

[SmashinMachine]

1 minute ago, Jumper118 said:

its does use the cpu lanes. the diagram is wrong or it cant do 3 way cf  

OK you think the diagramm is wrong. But why do this SLOT share the Lanes with the SATA ports???? sAta ports are connected to PCH........

from the manual_

[typographie]

14 minutes ago, SmashinMachine said:

Yes, I know that but you missunderstand my question...

The third Slot does NOT use the CPU Lanes, it uses the PCH lanes. How can these SLOT  use the Lanes from CPU???

I may be missing something big here, but is there a reason why the third card can't go through the PCH? Skylake has a DMI 3.0 connection, which as I understand runs at a speed equivalent to PCIe 3.0 4x. I don't know for sure this is what's happening, but I think the bandwidth is available to go PCIe slot 3 -> PCH -> CPU and get the 4x needed for three-way Crossfire.

[Jumper118]

i think the best thing to do would be to ask someone @asus 

[SmashinMachine]

4 minutes ago, typographie said:

I may be missing something big here, but is there a reason why the third card can't go through the PCH? Skylake has a DMI 3.0 connection, which as I understand runs at a speed equivalent to PCIe 3.0 4x. I don't know for sure this is what's happening, but I think the bandwidth is available to go PCIe slot 3 -> PCH -> CPU and get the 4x needed for three-way Crossfire.

explain me pls one thing:

IF I run in 1st Slot a GPU with x16 and in 3rd Slot a pcie SSD x4, then they make together 20 Lanes. Skylake CPU can only 16 Lanes. Where did this 4 lanes come from????

[Sintezza]

10 minutes ago, SmashinMachine said:

explain me pls one thing:

IF I run in 1st Slot a GPU with x16 and in 3rd Slot a pcie SSD x4, then they make together 20 Lanes. Skylake CPU can only 16 Lanes. Where did this 4 lanes come from????

If you put a pci-e ssd in a pci-e slot that is directly wired to the cpu.

Then your gpu will automaticly run in 8x mode.

 

Unless you use the bottom slot that gets its 4x lanes from the pch.

Z170 chipset provides 20 pci-e lanes, over dmi 3.0 bus.

[SmashinMachine]

Just now, Sintezza said:

If you put a pci-e ssd in a pci-e slot.

Then your gpu will automaticly run in 8x mode.

 

Unless you use the buttom slot that gets its 4x lanes from the pch.

Yes, we are taling about the bottom slot. How can you explain it when a gpu runs in this buttom slot???

That means GPU runs over PCH lanes... It does not make sense.,.... 

[SmashinMachine]

Any ideas????

[SmashinMachine]

2 hours ago, Jumper118 said:

i think the best thing to do would be to ask someone @asus 

So I spoke with ASUS...

They wrote, SLI will work up to x8/x8. If a motherboard supports x8/x4/x4 and a PCIe card is placed into that bottom slot, SLI will not work because only one GPU will have eight lanes. NVIDIA requires a minimum of PCIe X8 in order to enable SLI. 

z170 Chipset has 20(!) Pcie 3.0 Lanes to use in five sets of four lanes, and these could be used four GPUs as well. It can support x8/x8 from the CPU and PCIe 3.0 x4 from the chipset and end up with either dual-SLI or tri-CFX enabled when all the slots are populated. CFX would run at x8/x8/x4

[Jumper118]

4 minutes ago, SmashinMachine said:

So I spoke with ASUS...

They wrote, SLI will work up to x8/x8. If a motherboard supports x8/x4/x4 and a PCIe card is placed into that bottom slot, SLI will not work because only one GPU will have eight lanes. NVIDIA requires a minimum of PCIe X8 in order to enable SLI. 

z170 Chipset has 20(!) Pcie 3.0 Lanes to use in five sets of four lanes, and these could be used four GPUs as well. It can support x8/x8 from the CPU and PCIe 3.0 x4 from the chipset and end up with either dual-SLI or tri-CFX enabled when all the slots are populated. CFX would run at x8/x8/x4

interesting 

[typographie]

3 hours ago, SmashinMachine said:

explain me pls one thing:

IF I run in 1st Slot a GPU with x16 and in 3rd Slot a pcie SSD x4, then they make together 20 Lanes. Skylake CPU can only 16 Lanes. Where did this 4 lanes come from????

A Skylake system has 16 PCIe 3.0 lanes wired directly to the CPU which will be entirely devoted to your video card, and also up to 20 PCIe 3.0 lanes (limited to 4x speed, I think) coming from the PCH or chipset.

 

Take a look at the Z170 block diagram:

Spoiler

 

[SmashinMachine]

29 minutes ago, typographie said:

A Skylake system has two sets of PCIe lanes: you've got 16 PCIe 3.0 lanes wired directly to the CPU which will be entirely devoted to a single video card, and you've got up to 20 PCIe 3.0 lanes (limited to 4x speed, I think) coming from the PCH or chipset.

 

Take a look at the Z170 block diagram:

  Reveal hidden contents

 

Thanks, I tought that graphics can only use the lanes of cpu. The Z170 block diagram showed me that too. however...a gpu works over pch Lanes too

 

[typographie]

6 minutes ago, SmashinMachine said:

Thanks, I tought that graphics can only use the lanes of cpu. The Z170 block diagram showed me that too. however...a gpu works over pch Lanes too

I honestly don't know if a video card can be used with the chipset's PCIe lanes. If so, it would be limited to PCIe 3.0 4x. The 16 lanes from your CPU are usually used for graphics.

 

In my experience, my motherboard (Asus Z170-A) didn't even like it when I installed my GPU in my second PCIe x16 slot, which is also allocated lanes from the CPU. It really wanted it to be in the top slot. So I strongly doubt a video card can be used in chipset PCIe slots unless maybe it's the third card in three-way Crossfire as the OP was asking.

[SmashinMachine]

6 minutes ago, typographie said:

I honestly don't know if a video card can be used with the chipset's PCIe lanes. If so, it would be limited to PCIe 3.0 4x. The 16 lanes from your CPU are usually used for graphics.

 

In my experience, my motherboard (Asus Z170-A) didn't even like it when I installed my GPU in my second PCIe x16 slot, which is also allocated lanes from the CPU. It really wanted it to be in the top slot. So I strongly doubt a video card can be used in chipset PCIe slots unless maybe it's the third card in three-way Crossfire as the OP was asking.

I did not know that too. That was my problem.  I found it very hard to believe. And most z170 MBs are like that not only ASUS. 

Jumper118 suggested  me to call the ASUS

So I called the ASUS. I think you did not read that:

2 hours ago, SmashinMachine said:

So I spoke with ASUS...

They wrote, SLI will work up to x8/x8. If a motherboard supports x8/x4/x4 and a PCIe card is placed into that bottom slot, SLI will not work because only one GPU will have eight lanes. NVIDIA requires a minimum of PCIe X8 in order to enable SLI. 

z170 Chipset has 20(!) Pcie 3.0 Lanes to use in five sets of four lanes, and these could be used four GPUs as well. It can support x8/x8 from the CPU and PCIe 3.0 x4 from the chipset and end up with either dual-SLI or tri-CFX enabled when all the slots are populated. CFX would run at x8/x8/x4