PCIe CPU and PCH ?

[Elochai]

So it been a good many of years now since I needed an upgrade but it is time as my 10 year old system is now dying and its OC card has out lived its performance days.

 

Things have changed over the years, and by the way if Linus, Luke, or anyone else with LTT sees this, I think it be a great video to explain to users like me.

 

So here the deal, I'm looking to go some what over board again on a new PC like I did with my last one to try and get a good enough life cycle out of it (10 Years again would be great). So this time around I was planning to do SLI of two 1080's so 6 years down the road they be still running strong, and I want to do a M.2 drive for my OS and main programs. The CPU I was thinking of was the 6700K.

 

Now here the thing, The 6700k from what I am understanding only supports 16x max in lanes. Now splitting that into two 8x lanes for the video cards is more then enough from what I see people saying. But how will that effect me for the m.2 drive that needs a 4x lane open on the PCIe.

 

And what is this PCIe PCH ? The motherboard I am looking at says it has three 16x (CPU) lanes (Don't understand how you can support three when the max is one 16x lane support max on that CPU) and it has one x16 (PCH) slot and one 1x (PCH) slot. So what are these PCH PCIe slots and how do they work vs the ones linked by the CPU ?

 

By the way the board is an ASUS MAXIMUS VIII EXTREME

[Cracklingice]

The PCIe for the M.2 slots come from the Z170 chipset (and share bandwidth with some of the sata express ports so they'll get disabled) - as do all the pci-e x1 slots on the motherboard.  The 16 lanes from the cpu work like such.
1 video card (top slot) 16x

2 video cards (top slot and middle slot) 8x, 8x

3 video cards (all 3 16 slots) 8x, 4x, 4x

 

Check this thread and definitely expand the hidden contents.

[Elochai]

Thanks for the replay Cracklingice.

 

So just see if I am understanding this right. I should be able to use two 1080's on at x8 on the CPU lanes for PCIe, the M.2 drive will use the x4 lane through the z170 chipset. And if down the road I put in another PCIe card or two such as SSD, or a Raid card, or whatever, it will use the z170 chipset up to it limit of 20x if reached by devices ?

[Glenwing]

7 minutes ago, Elochai said:

Thanks for the replay Cracklingice.

 

So just see if I am understanding this right. I should be able to use two 1080's on at x8 on the CPU lanes for PCIe, the M.2 drive will use the x4 lane through the z170 chipset. And if down the road I put in another PCIe card or two such as SSD, or a Raid card, or whatever, it will use the z170 chipset up to it limit of 20x if reached by devices ?

Slots are physically hardwired to either the CPU or the PCH. Whether a device uses lanes from the CPU or PCH depends on which slot it's plugged into. If you plug it into one of the main x16 slots, it will use lanes from the CPU no matter what type of device it is. M.2 slots are wired to the chipset. Many Z170 motherboards (or previous generation equivalents) also have their bottom x16 slots wired through the chipset too (and they are usually just x4 slots dressed up as x16 slots).

[Cracklingice]

10 hours ago, Elochai said:

Thanks for the replay Cracklingice.

 

So just see if I am understanding this right. I should be able to use two 1080's on at x8 on the CPU lanes for PCIe, the M.2 drive will use the x4 lane through the z170 chipset. And if down the road I put in another PCIe card or two such as SSD, or a Raid card, or whatever, it will use the z170 chipset up to it limit of 20x if reached by devices ?

This is how it should work but not all manufacturers implement things exactly the same so if you look in the manual of the motherboard you are interested in purchasing it may help to clarify.  You can typically download the pdf from the manufacturer website.  If you're browsing on newegg, click the warranty page and there's typically a direct link to the product page from the manufacturer.  Also, do keep in mind that all of the chipset pcie slots and other items connected to those slots reach the CPU through a single DMI 3.0 connection that is  8 GT/s transfer rate per lane, with a total of 4 lanes totalling 3.93 GB/s for the CPU to PCH link.  Items built into the chipset by the manufacturer also take out of that 20 lane pool so things such as the sata / sata express hubs and other items use those available lanes.  It's why each m.2 card you install will disable one sata / sata express hub each.

10 hours ago, Glenwing said:

Slots are physically hardwired to either the CPU or the PCH. Whether a device uses lanes from the CPU or PCH depends on which slot it's plugged into. If you plug it into one of the main x16 slots, it will use lanes from the CPU no matter what type of device it is. M.2 slots are wired to the chipset. Many Z170 motherboards (or previous generation equivalents) also have their bottom x16 slots wired through the chipset too (and they are usually just x4 slots dressed up as x16 slots).

I've not heard of a motherboard with the third pcie x16 physical slot on the pch.  Is there a particular model you were thinking of?  Maybe it's the boards that support 4 physical x16 slots where the bottom isn't direct cpu link.  I don't have any need for four x16 slots so I haven't really looked into them.

[Glenwing]

7 hours ago, Cracklingice said:

I've not heard of a motherboard with the third pcie x16 physical slot on the pch.  Is there a particular model you were thinking of?  Maybe it's the boards that support 4 physical x16 slots where the bottom isn't direct cpu link.  I don't have any need for four x16 slots so I haven't really looked into them.

There are a lot of boards set up that way. It's easier to tell on Z97 and older generations, because the PCH still uses PCIe 2.0 while the CPU uses 3.0, so you can look at the spec sheet.

 

ASUS Z97 Maximus VII Hero: https://www.asus.com/us/Motherboards/MAXIMUS_VII_HERO/overview/

2 x PCIe 3.0/2.0 x16 (x16 or dual x8, red) 
1 x PCIe 2.0 x16 (x4 mode, black)

 

ASUS Z97 Deluxe: https://www.asus.com/us/Motherboards/Z97DELUXENFC_WLC/specifications/

2 x PCIe 3.0/2.0 x16 (x16 or dual x8) 
1 x PCIe 2.0 x16 (max at x4 mode)

 

Gigabyte GA-Z97X-Gaming 3: http://www.gigabyte.com/products/product-page.aspx?pid=4966#ov

1 x PCI Express x16 slot, running at x16 (PCIEX16)

1 x PCI Express x16 slot, running at x8 (PCIEX8)
* The PCIEX8 slot shares bandwidth with the PCIEX16 slot. When the PCIEX8 slot is populated, the PCIEX16 slot will operate at up to x8 mode. (The PCIEX16 and PCIEX8 slots conform to PCI Express 3.0 standard.)

1 x PCI Express x16 slot, running at x4 (PCIEX4)
* The PCIEX4 slot shares bandwidth with all PCI Express x1 slots. All PCI Express x1 slots will become unavailable when a PCIe x4 expansion card is installed.

3 x PCI Express x1 slots
(The PCIEX4 and PCI Express x1 slots conform to PCI Express 2.0 standard.)

 

 

Z170 is harder to tell, but Gigabyte still provides block diagrams of the motherboard layout, so we can see this configuration is still used on some Z170 boards.

 

 

[Cracklingice]

21 minutes ago, Glenwing said:

There are a lot of boards set up that way. It's easier to tell on Z97 and older generations, because the PCH still uses PCIe 2.0 while the CPU uses 3.0, so you can look at the spec sheet.

 

ASUS Z97 Maximus VII Hero: https://www.asus.com/us/Motherboards/MAXIMUS_VII_HERO/overview/

2 x PCIe 3.0/2.0 x16 (x16 or dual x8, red) 
1 x PCIe 2.0 x16 (x4 mode, black)

 

ASUS Z97 Deluxe: https://www.asus.com/us/Motherboards/Z97DELUXENFC_WLC/specifications/

2 x PCIe 3.0/2.0 x16 (x16 or dual x8) 
1 x PCIe 2.0 x16 (max at x4 mode)

 

Gigabyte GA-Z97X-Gaming 3: http://www.gigabyte.com/products/product-page.aspx?pid=4966#ov

1 x PCI Express x16 slot, running at x16 (PCIEX16)

1 x PCI Express x16 slot, running at x8 (PCIEX8)
* The PCIEX8 slot shares bandwidth with the PCIEX16 slot. When the PCIEX8 slot is populated, the PCIEX16 slot will operate at up to x8 mode. (The PCIEX16 and PCIEX8 slots conform to PCI Express 3.0 standard.)

1 x PCI Express x16 slot, running at x4 (PCIEX4)
* The PCIEX4 slot shares bandwidth with all PCI Express x1 slots. All PCI Express x1 slots will become unavailable when a PCIe x4 expansion card is installed.

3 x PCI Express x1 slots
(The PCIEX4 and PCI Express x1 slots conform to PCI Express 2.0 standard.)

 

 

Z170 is harder to tell, but Gigabyte still provides block diagrams of the motherboard layout, so we can see this configuration is still used on some Z170 boards.

 

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Interesting.  Thanks for including the block diagram.  Guess this gigabyte board falls into the how different manufacturers implement things differently part of my post.  It shouldn't be hard to find block diagrams, but some manufacturers just don't make them available.  It's lame.