M.2 pcie lanes question

[STiCory]

OK, please don't kill me, but I want to beat this horse one more time ?

In all seriousness, I can't find this actual question answered anywhere! Basically what I want to know is this, do PCIe 3.0 x4 based M.2 use PCIe lanes from the CPU or the chipset? Based off of that, assuming it uses CPU lanes, that means that all FCLGA 1151 processors (being that they only have 16 lanes) can I let run a graphics card at x8 if an x4 m.2 drive is used, correct? If it goes through the chipset, is the DMI 3.0 link a bottleneck? Assuming the most badass NVME drives can read at 3.2GB/s that only leaves a theoretical 700MB for the rest of the DMI link for all other peripherals.

Thoughts?

 

School me please!

[Mira Yurizaki]

M.2 slots always use the chipset's PCIe lanes, unless you're using an X99 board in which it will use the CPU's (but those CPUs have like 40 lanes anyway)

 

As far as the DMI issue goes, unless you're peripherals are all blasting data at once, the bottleneck is a non-issue.

[Electronics Wizardy]

It uses lanes from the chipset for m.2

 

Dmi isn't a limit for most users

 

Gpu is at 16x

[NumLock21]

On X99, M.2 runs off the CPU.

For mainstream it runs off the chipset. Now if it runs off the CPU, then it will depend on which board you get. Boards that allocated all lanes from the CPU to the 1st x16 slot will not be able to share lanes, because when you plug in a video card it eats up all the lanes leaving nothing for the M.2

Boards that can do SLI that is x8/x8 can share lanes with the M.2

So video card first eats 16 lanes from CPU

Plug in M.2 then video card only eats 8 lanes from CPU.

M.2 eats up 4 lanes from CPU

You're 4 lanes left over that can't be used for other devices.

[STiCory]

1 hour ago, M.Yurizaki said:

M.2 slots always use the chipset's PCIe lanes, unless you're using an X99 board in which it will use the CPU's (but those CPUs have like 40 lanes anyway)

 

As far as the DMI issue goes, unless you're peripherals are all blasting data at once, the bottleneck is a non-issue.

 

1 hour ago, Electronics Wizardy said:

It uses lanes from the chipset for m.2

 

Dmi isn't a limit for most users

 

Gpu is at 16x

 

1 hour ago, NumLock21 said:

On X99, M.2 runs off the CPU.

For mainstream it runs off the chipset. Now if it runs off the CPU, then it will depend on which board you get. Boards that allocated all lanes from the CPU to the 1st x16 slot will not be able to share lanes, because when you plug in a video card it eats up all the lanes leaving nothing for the M.2

Boards that can do SLI that is x8/x8 can share lanes with the M.2

So video card first eats 16 lanes from CPU

Plug in M.2 then video card only eats 8 lanes from CPU.

M.2 eats up 4 lanes from CPU

You're 4 lanes left over that can't be used for other devices.

Awesome. Thank you for the help guys! Where did you guys learn this? I couldn't find that answer anywhere haha

For reference this is the MOBO I'm looking at with this M.2 NVMe drive.

[STiCory]

Ya know FWIW this forum rocks, I've posted a couple questions so far and have got nothing but awesome answers and super helpful people.

 

Thanks for the help guys, hopefully I can eventually help the community like they always help me!

[STiCory]

Selected best answer because it's the same as the others and he was the first poster!

[NumLock21]

1 hour ago, STiCory said:

 

Awesome. Thank you for the help guys! Where did you guys learn this? I couldn't find that answer anywhere haha

For reference this is the MOBO I'm looking at with this M.2 NVMe drive.

Read as much info as you can get, and you'll eventually understand how it works. Taking your board as a example. When you plug the M.2 drive into the M.2 slot on the board it uses lanes from the chipset. Now if you take your M.2 along with a PCIe M.2 adapter card, and plug that into the PCIe x16 slot, then it will use the lanes from the CPU because CPU lanes are wired to that slot. 99% of the time M.2 uses lanes from the chipset. Plug it to a slot where it's wired to the CPU, then your M.2 will use lanes from the CPU not from the chipset.

[STiCory]

11 hours ago, NumLock21 said:

Read as much info as you can get, and you'll eventually understand how it works. Taking your board as a example. When you plug the M.2 drive into the M.2 slot on the board it uses lanes from the chipset. Now if you take your M.2 along with a PCIe M.2 adapter card, and plug that into the PCIe x16 slot, then it will use the lanes from the CPU because CPU lanes are wired to that slot. 99% of the time M.2 uses lanes from the chipset. Plug it to a slot where it's wired to the CPU, then your M.2 will use lanes from the CPU not from the chipset.

Interesting for sure. I wonder how long it'll take until NVMe drives saturate the DMI3 link and at what real world speed it happens! I can't imagine of speeds nearing 4GB/s. For reference my current rig is an i5 650 on an old p55 with a WD RE500 drive ASA primary ?. Talk about old and slow haha.