Z170-Deluxe / M.2 PCIe Question

Anytime you have more than 1 device in an PCIe slot, you are using PCIe lanes. And there are still only 16 lanes available to the slots.

There are some new PCIe 3.0 type lanes available from the chipset, but those are restricted to x4 lanes per device. So your M.2 x4 just used one of those sets, and the USB ports use some, and SATA ports use some and so on...

Its still pretty much the same rules its been all along, but we have some new devices now, and one new slot type.

MarkW is correct. Your shiny new Z170 board has the nice additional PCI lanes made just for storage devices like your M.2. But now that you have that used up along with the other connections he mentioned, you will be robbing from the graphics card, and it will drop down to x8 speeds (which isn't the end of the world- just a tiny hit in performance). But - I would rather just run two SATA III 6Gb/s SSDs in Raid 0, or even just as single drives. They are still plenty fast and you would leave the graphics card at x16.


BTW, how do you like your Skylake rig? Your's is similar to mine and I'm loving it! Freakin' awesome.

Firstly, if it WAS to steal bandwidth, it would not make your card run like if SLI -that requires 2 cards- it would run it at x8.

The 6700k CPU only supports 16 PCIe lanes .. so if you run a card at full x16 speed -adding any other PCIe card to the bus would force card to run at x8 (although you probably would NOT notice a difference in performance...as the actually speed of the bus itself is nowhere near saturated even under load..)

PCI Express Revision 3.0
PCI Express Configurations ‡ Up to 1x16, 2x8, 1x8+2x4
Max # of PCI Express Lanes 16
http://ark.intel.com/products/88195/Intel-Core-i7-6700K-Processor-8M-Cache-up-to-4_20-GHz

Compared to the 28/40 lanes provided by the Haswell-E chips. Really this just makes SLI/XFIRE configurations different/possible or impossible at different speeds/configs.

NerdIT, I know you are correct about the i7 6700k only having 16 PCIe lanes, but are you sure about adding any PCIe card -automatically dropping the card to x8? I was under the impression the Z170 chipset has 20 PCIe lanes, 16 of which are used by SATA, USB, etc... So a single x4 is left over for a PCIe storage device.

http://www.computershopper.com/components/reviews/intel-core-i7-6700k/(page)/2#review-body

That review by Computer Shopper's Matt Safford states "For starters, Z170 boards will support up to 20 PCIe 3.0 lanes, rather than the eight lanes of PCIe 2.0 provided by standard Z97 boards. (That is in addition to the 16 PCIe 3.0 lanes provided by the CPU, which remains the same with Skylake.) The extra lanes come thanks to an upgrade to the DMI interface that connects the CPU to the chipset, and they are important, given the rising prevalence of PCIe-based storage (via M.2, SATA Express, or drives that plug directly into a PCI Express slot, like Intel’s SSD 750 Series)."

If I'm not understanding this correctly please enlighten me (I'm not being sarcastic, I am really asking)...

I think we still need to have someone take an NVMe PCIe device, and add it into a Z170 based motherboard, and do the difficult work required to figure out which lanes are being used and which lanes are not being used. Because if Intel and Micron what to push these Optane (XPoint) cards into the market, I think they need to do it by NOT affecting other PCIe lane setups. Because the very people that would have enough cards to be affected by the Optane cards are the ones that are going to be the first adapters of Optane.

Optane is sexy so far. 1000x faster, 1000x duration, and 10x the density. Those are incredible jumps in technology. Now we need to see two more things. Price. And how PCIe is affected by adding an Optane NVMe card. And that will not happen until sometime in 2016.

+1.

Well said, and exactly what I was thinking.

Skylake based motherboards have the standard 16 PCIe 3.0 lanes from the CPU, and whats new is that the chipset now has 26 HSIO (HIgh Speed I/O) PCIe 3.0 lanes that are allocated for I/O ports. You can see in the chart below how the PCIe lanes are designated. Motherboard manufacturers can reallocate some of those lanes to support other things. I am not yet certain what all those other things consists of yet. But we will find out over time.

It would depend from what I am getting. First of all, not all M.2 NVMe drives are the same. If you have two x4 drives though, then yes I believe your card will drop to x8. But what exact NVMe drive are you talking about?

I would connect a single M.2 drive, and then check it with AIDA 64 or HWINFO64 and see what it says your drive is operating at. Those same utilities or GPUz will tell you if the graphics card is operating at a full x16.

At this point it is still about as clear as mud, because it looks like mobo manufacturers can allocate the lanes in different manners, and like I said some drives are x2 and others are x4.

Like this awesome Samsung is x4.
http://www.anandtech.com/show/9702/samsung-950-pro-ssd-review-256gb-512gb

From the article:
"While some vendors have put out M.2 PCIe devices that support two lanes of PCIe, Samsung went straight for four lanes with the XP941" drive"

Sorry to say, but if this many PCIe lanes are important to you, it sounds like LGA2011v3 might have been a better platform, for you.

It all depends on how the motherboard is designed, and what lanes from the chipset are assigned to which devices.

The 16 PCIe lanes from the CPU should still be assigned to the PCIe slots though.
M.2 x4 slots should come only from the chipset. As should all I/O ports.

Check this out:
http://www.enthusiastpc.net/articles/00003/2.aspx

You should read the whole thing as it is very informative, but here's a part of it explaining how Intel chips work with PCIe (note what i put in bold) I know this talks about LGA-1155- but the restriction is in Intel chips itself.

"On the previous page we touched on the AMD architecture concerning PCI Express where these 2 facts will be important in understanding the difference with the various Intel architectures:

The chipset determines the total number of available PCI Express lanes
How these lanes are routed on the mainboard (onboard devices and slots of various sizes) is mostly up to the mainboard manufacturer

As you might know, Intel 1155 mainboards do not have a Northbridge chip. In some ways this makes things easier for the mainboard manufacturers but it also limits things.

The primary PCI Express lanes (the ones used for graphics cards) on Intel 1155 mainboards do not originate from the Northbridge chip (as there isn't one) but instead originate from the CPU. While this makes mainboard design somewhat easier (less physical connections to route) it is also very restrictive. Remember, PCI Express lanes are physical connections on the mainboard that run from one chip to another chip or to a slot.

Intel Sandy Bridge processors using socket 1155 have only 16 physical lanes that run from the processor to the primary graphics slot or slots. These lanes are generally only used to connect graphics cards. This limits all socket 1155 processors to 16 lanes for graphics. On the simplest boards you will only find a single x16 slot that will hold a graphics card.

On SLI / CrossfireX capable boards you will find mostly 2 physical x16 sized slots for graphics cards. If only one graphics card is used in the primary slot, all 16 lanes from the processor socket will connect to this slot. However, if a videocard is inserted into the second x16 slot, the mainboard reroutes 8 of the 16 lanes from the primary slot to the secondary slot. The end result is that 8 physical lanes connect to each of the 2 slots.

It's important to take note of how this was written down: if slot 2 is populated, both slots operate with 8 lanes."



EDIT: So they fixed this with socket 2011 chips, I am looking for more info on LGA 1151 specifically