Planning for PCIe Lane Usage

[derekbischoff]

I want to try a build with the new i7 7700k (which has a max # of lanes to be 16), the MSI GeForce GTX 1060 Gaming X 6GB graphics card, and the ASRock Fatal1ty Z270 Gaming K6. From reading MSI's site, the graphics card is 16x, which would max out the # of lanes the CPU can handle. I would also like to add a PCIe SSD and possibly a WiFi/BT module. I was wondering how adding the PCIe SSD would affect the lane situation. Also, would a M.2 SSD affect the lane situation the same as a PCIe SSD?

[ARikozuM]

You get an extra X from the chipset for any other devices you have.

[Droidbot]

M.2, PCI-E x1 (ie Wifi/Bt cards, etc), GbE and one x4 slot are provided by the Skylake chipset, whereas GPUs use the CPU's PCI-E lanes. 

[derekbischoff]

3 minutes ago, ARikozuM said:

You get an extra X from the chipset for any other devices you have.

What do you mean by an extra X? I was seeing some places that the chipset allows for more lanes. So these extra lanes provided by the chipset would cover the SSD?

 

Thanks for the quick reply on the original posting!

[RadiatingLight]

I believe the chipset also has 4 PCI-e Gen 2 lanes, so you should be fine. I think kaby lake chipsets have even more than 4 pcie lanes, so all should be good

[ARikozuM]

1 minute ago, derekbischoff said:

What do you mean by an extra X? I was seeing some places that the chipset allows for more lanes. So these extra lanes provided by the chipset would cover the SSD?

Your chipset will provide more lanes (how many depends on the generation) and the controller on add-in cards will sometimes ask for DMI or CPU lanes. 

 

[AnonymousGuy]

Chipset gives another 8 lanes.  Regardless, even if you load up cards you'll get x8,x4,x4 which is good enough for everything.

[manikyath]

9 minutes ago, AnonymousGuy said:

which is good enough for everything.

except nvidia requires you to have x8 slots for your GPUs

[AnonymousGuy]

3 minutes ago, manikyath said:

except nvidia requires you to have x8 slots for your GPUs

I think all mobos support 8/8/4 with the CPU + chipset lanes.  If you're going hardcore they ofc want you to move up to x99.

[NumLock21]

CPU give you 16 lanes. Chipset gives you 24 lanes. In total, you'll have 40 lanes. Plenty for whatever you want to throw in. Depending on the board you buy, low end Z270 that does not support SLI, will allocated all 16 lanes from the CPU into the 1st x16 slot. Leaving everything else to be handled by the chipset. Z270 that does support SLI will split the lanes from the CPU to 2 x16 slots, freeing up the lanes that that has to be used by the chipset. Get a board that supports SLI, so you won't have pcie lane distribution problems later on.

[manikyath]

5 minutes ago, AnonymousGuy said:

I think all mobos support 8/8/4 with the CPU + chipset lanes.  If you're going hardcore they ofc want you to move up to x99.

i'm actually not sure about that one, you'd have to make double damn sure about it in the mobo spec sheet if that's something you want to rely on

[NumLock21]

Z270 that does SLI is x8/x8/x4

Low end Z270 and the rest is x16/x4 or x16/x4/x4

[mariushm]

Ok, so Intel i7700k  has 16 pci-e v3.0 lanes, which can be arranged by the motherboard manufacturer as 1x16 , 2x8 or 1x8 + 2x4  See https://ark.intel.com/products/97129/Intel-Core-i7-7700K-Processor-8M-Cache-up-to-4_50-GHz

For example, from the bios or using automatic switching ICs, if there are two video cards installed in the first two pci-e slots, the motherboard can switch both slots to x8.

 

The processor communicates to the chipset using DMI 3.0 with 8 GT/s which is a communication channel that's more or less equal to a pci-e v3.0 x8 , or in other words you have 8 GB/s in both directions, between the chipset and the processor.

The chipset has several things that are connected to this 8 GT/s bus (and share this bandwidth), the SATA controller, the USB 3 controllers and other things.  Among "other things", there's a PCI Express controller which creates several pci-e v2.0 or v3.0 lanes  which are then used for example to connect to the onboard sound card, network card, to create additional pci-e x1 and x4 slots. 

Since you don't have all hard drives transferring at their maximum speed AND the usb 3.0 ports communicating at maximum speed AND pci-e slots working at full speed, it's OK to squeeze all these things into a single channel to the processor that's running at a relatively low speed (only about 8 GB/s in both directions)

 

Now here comes the differences between chipsets ... lower end chipsets may only talk to the processor at lower speed (for example H110 works with DMI 2.0 and 5 GT/s instead of DMI 3.0 and 8 GT/s) or create less pci-e lanes to be used to connect things to chipset.

 

For example H110 creates only 6 pci-e v2.0 lanes (each with 500MB/s speed in both directions), while B150 chipset creates 8 pci-e v3.0 lanes (with 1GB/s in both directions) and Z170 creates up to 20 pci-e v3.0 lanes from the chipset.

 

See this for more details about differences between chipsets : https://www.pugetsystems.com/labs/articles/Z170-H170-H110-B170-Q150-Q170---What-is-the-Difference-635/