Skylake PCI-E Lanes

[Nailo55]

Hello, i recently bought a computer (without hardly any knowledge, stupid of me)..

My build has an AMD FX 9590 (regret buying it), the case is small, and hardly provides positive airflow, and my cpu was overheating even with watercooling!@!@! Now, onto my question with skylake..

I am upgrading, and want to know if the new Skylake CPU's can support 2-way SLI (x8/x8), with a M.2 connection and 1 SATA HDD connected? Cause I do know Skylake only supports 1 x16 GPU, and 1 x8 GPU. So in return it would be a x8/x8 setup. Now, my 2nd question is would the M.2 interfere with my 2-way SLI GPU setup? Or would it just interfere with sata connections (on some motherboards)?

 

[Suztera]

No it should not interfere as the m.2 should run with the extra 4 pcie lanes on the chipset on Z170 motherboards.

 

[Nailo55]

Alright, thank you very much! I should have done more research before buying my first High-end Gaming PC... But, as they say "crap happens" (expensively) lol.

Again, thank you for your reply.

 

[EasyLover]

Just for reference purpose, on Skylake architecture, CPU has maximum of 16 PCI lanes in config (1x16, 2x8 and where possible 1x8 and 2x4) where as upto 20 PCI lanes would be coming from Chipset for storage drives. So, SLI of two graphics card would run from CPU directly whereas M.2 port would drive 4 PCI lanes from chipset. It will not interfere with the SLI.

 

[Kordanor]

Just for reference purpose, on Skylake architecture, CPU has maximum of 16 PCI lanes in config (1x16, 2x8 and where possible 1x8 and 2x4) where as upto 20 PCI lanes would be coming from Chipset for storage drives. So, SLI of two graphics card would run from CPU directly whereas M.2 port would drive 4 PCI lanes from chipset. It will not interfere with the SLI.

How exactly does the board chose whether it takes the CPU lanes or the Board lanes?
Will Hard Drives always connect with the Chipset lanes, so that the CPU lanes stay "free"?
Or are all M.2 and Sata lanes connected to the Chipset, whil all the physical PCI Slots are automatically going to the CPU?
So will a PCI SSD automatically connect to the CPU and basically screw a SLI setup?

 

[EasyLover]

Just for reference purpose, on Skylake architecture, CPU has maximum of 16 PCI lanes in config (1x16, 2x8 and where possible 1x8 and 2x4) where as upto 20 PCI lanes would be coming from Chipset for storage drives. So, SLI of two graphics card would run from CPU directly whereas M.2 port would drive 4 PCI lanes from chipset. It will not interfere with the SLI.

1. How exactly does the board chose whether it takes the CPU lanes or the Board lanes?
2. Will Hard Drives always connect with the Chipset lanes, so that the CPU lanes stay "free"?
3. Or are all M.2 and Sata lanes connected to the Chipset, whil all the physical PCI Slots are automatically going to the CPU?
4. So will a PCI SSD automatically connect to the CPU and basically screw a SLI setup?

1. The first two PCIe x16/x8 3.0 lanes are directly hooked up with the CPU, so they will take lanes from CPU regardless of the configuration.
2. Yes, SATA HDDs will always be connected to Chipset lanes be it ASMedia (or any third party implementation) or Native Intel's chipset.
3. Like I mentioned in para-1, above, Any thing connected on first two PCIe 3.0 x16/x8 lanes will be taking PCIe lanes from CPU. M.2 slot will be sharing Chipset PCIe lanes.
4. If a PCIe SSD is installed in first or second PCIe 3.0 x16/x8 slot then it would take lanes from CPU and if it is connected in last PCIe 3.0 x4 slot then it would be taking lanes from chipset.

My answer is on the assumption that we are not talking about VERY high end solutions from the manufacturers like Gigabyte Gaming G1 board which has PLEX chip implemented but in MOST of the cases, answers will hold.

Regards,

 

[Kordanor]

Thank you! Just one more example to make sure I got it right:

Let's take this Picture:
http://images.anandtech.com/doci/9485/Z170%20Pro%20Gaming_01.jpg

From Top to bottom there are 6 PCI Slots:
PCIEX 1_1
PCIEX 16_1
PCIEX 1_2
PCIEX 16_2
PCIEX 1_3
PCIEX 16_3

If I plug two Graphics Cards into 16_1 and 16_2 and a SSD into any other slot it should work fine as the 16 slots have priority, even if it is PCIEX 1_1
If I plug one Graphics Card into 16_1 and one SSD into 16_2, then there would not be enough lanes left for another graphics card (SLI) into 16_3.
If I only plug one Graphics Card into 16_1 and one SSD into PCIEX 1_3 then both would be handled by the CPU as the lanes aren't needed otherwise.

 

[EasyLover]

Thank you! Just one more example to make sure I got it right:

Let's take this Picture:
http://images.anandtech.com/doci/9485/Z170%20Pro%20Gaming_01.jpg

From Top to bottom there are 6 PCI Slots:
PCIEX 1_1
PCIEX 16_1
PCIEX 1_2
PCIEX 16_2
PCIEX 1_3
PCIEX 16_3

If I plug two Graphics Cards into 16_1 and 16_2 and a SSD into any other slot it should work fine as the 16 slots have priority, even if it is PCIEX 1_1
If I plug one Graphics Card into 16_1 and one SSD into 16_2, then there would not be enough lanes left for another graphics card (SLI) into 16_3.
If I only plug one Graphics Card into 16_1 and one SSD into PCIEX 1_3 then both would be handled by the CPU as the lanes aren't needed otherwise.

Out of these six PCIe slots, PCIEX 16_1 and PCIEX 16_2 are drawing lanes from CPU while all other PCIEX slots are drawing lanes from Chipset.

If you are going for SLI/CF then options are first card in PCIEX 16_1 and second card in PCIEX 16_2. This way both card will draw x8/x8 lanes from CPU.

Now if you want to add PCIe SSD as well along with two graphics card, add that SSD on PCIEX 16_3 and in the BIOS set its speed to x4 as by default the slot speed is set at x2.

Remember PCIEX 16_3 is x4 slot and it is taking PCI lanes from chipset.

If you would plug one graphics card in PCIEX 16_1 and SSD on PCIEX 16_2 then your card will operate at x8 not at x16 and SSD would get x8 lanes as well which is of no use unless SSD is rated at x8. Most of the PCIe SSDs are rated x4.

If you would insert one graphics card on PCIEX 16_1 and SSD on PCIEX 16_3 then graphics card will get all 16 lanes from CPU and SSD will get 4 lanes from chipset (not from CPU) as PCIEX 16_3 is taking lanes from the chipset.

 

[Kordanor]

Thanks again!

 

[anutter223]

I Have one question to all of this i have bad english / comprehension sorry in advance...

I have a 6700k already built on a z170x-ud5 Gigabyte mobo.

2 gtx 980 ti one in a PCI x16 (x16) and PCI x16 (x8) slot SLI they are runing in x8/x8

i want to add a LSI RAID Controller. will it work since im using all 16 lanes????

 

[EasyLover]

I Have one question to all of this i have bad english / comprehension sorry in advance...

I have a 6700k already built on a z170x-ud5 Gigabyte mobo.

2 gtx 980 ti one in a PCI x16 (x16) and PCI x16 (x8) slot SLI they are runing in x8/x8

i want to add a LSI RAID Controller. will it work since im using all 16 lanes????

Since you are already using two PCIe Gen 3 lanes which are directly taking lanes from CPU. Your only option is to install the RAID Controller on last PCIe lane which is taking lanes from chipset. Unfortunately, that PCIe lane is rated at x4 so even if your RAID Controller is rated at x8, you won't be able to utilize its full potential. Had that you were not using SLI configuration, you could have adopted to install the RAID Controller on second PCIe lane from CPU. But, in that config, your graphics card would operate at x8 as well.