Need help clearing up PCI lane misconceptions

[Mochithecat]

I was looking into building a PC and have been stressing over trying to find out how these lanes worked (the one that i wanted most at present was the i7 7700). Just about all the Intel processors I looked at outside the extreme series always seemed to have only 16 PCI 3 lanes.

From all the different pages I've visited on this subject, I usually got clashing information or just didn't quite get it.

Theoretical situation: If I had a GPU which used 16x lanes, but wanted an NVMe drive which used up 4x lanes. how would this impact the GPU? Would that just split it up 12-4? What other kinds of things would I need that would take from this initial lane cap?

I also read something about a chipset on the board adding additional lanes PCI 3 lanes depending on the chipset (I'm not quite sure what these all do just yet either). Am I missing something?

 

[13thmonkey]

the chipset has up to an additional 24, depending on the chipset. https://en.wikipedia.org/wiki/LGA_1151

 

[patrick47018]

Well it can be a bit complicated, I believe that some of the information you may seek can be found in this thread http://www.tomshardware.com/answers/id-2405813/pci-lanes-work.html
I also found this video and this guy seems to do a pretty good job at explaining it https://www.youtube.com/watch?v=vhw5xNhAO9A

 

[Mochithecat]

and here is where the clashing information seems to get to me.

in monkeys answer, chipsets add more depending on its support, so if i had say an H170 which supports 16 lanes, id have 32 max lanes to work with?

and in patricks answer, the video only talks about cpu having a max limit and its shared completely within only the cpu, and unless i missed it, chipset was never mentioned adding more.
and the thread has a couple posts. one saying that an on board chipset gave a few more,
and numerous other posts in the thread, implying or saying depending on who you read from, that it splits between whats on the cpu and/or doesnt believe the chipset adds more and only controls it.

that would leave me back full circle to what i was initially thinking; that i need a chipset that matches the max in the cpu that i was intending to use. this is really making me think that nobody, or at least many people dont know for sure due to the split, has a concrete answer to this kind of subject.

im really not trying to be rude or anything, but ive been searching for hours on this subject and its still not clear.

EDIT: ive been rereading more into other threads and some people are saying things like if you filled your pci 3 and a 1x wireless card works, its likely on a pci 2? is this motherboard related or something? this just feels like more variables to an undecided on answer.

 

[patrick47018]

So the lanes from the CPU are used for your graphics cards, and the motherboards chipset may have other lanes set aside for things such a storage.
This image might help

 

[13thmonkey]

^ what he said, there is no confusion, only people who understand it, and those that don't.

 

[Mochithecat]

so monkeys answer was right that the chipset adds support for extra lanes to work with?
just so im not misunderstanding the image, 8 Gb/s each 1x doesnt mean it only supports 1x cards, i can use anything as long as the total in that example is a max of 20 or less meaning 36 lanes are possible in that board cpu example right?

 

[13thmonkey]

so monkeys answer was right that the chipset adds support for extra lanes to work with?
just so im not misunderstanding the image, 8 Gb/s each 1x doesnt mean it only supports 1x cards, i can use anything as long as the total in that example is a max of 20 or less meaning 36 lanes are possible in that board cpu example right?

You can use anything that the mobo allows you to use. Some will be used for Sata, USB, sound card, network port etc. leaving the CPU ones for the GPUs.

Strongly suggest that you read mobo reviews or the manual, it should indicate what you can/cannot do at the same time. You may find that there are no 'slots' available just functionality that you can use or not use. Or some may have provided slots, which if you use them, you lose other functionality. Recent AMD mobo reviews have been indicating that using sata express loses 2 sata ports, etc.

 

[Mochithecat]

so monkeys answer was right that the chipset adds support for extra lanes to work with?
just so im not misunderstanding the image, 8 Gb/s each 1x doesnt mean it only supports 1x cards, i can use anything as long as the total in that example is a max of 20 or less meaning 36 lanes are possible in that board cpu example right?

You can use anything that the mobo allows you to use. Some will be used for Sata, USB, sound card, network port etc. leaving the CPU ones for the GPUs.

Strongly suggest that you read mobo reviews or the manual, it should indicate what you can/cannot do at the same time. You may find that there are no 'slots' available just functionality that you can use or not use. Or some may have provided slots, which if you use them, you lose other functionality. Recent AMD mobo reviews have been indicating that using sata express loses 2 sata ports, etc.

i will likely do that when ive picked out a board, thanks for the reminder and tip regarding potential functionality mishaps.

im so sorry to spring this up one last time as you really shouldnt have to reiterate it so many times to me, but i just want a yes or no answer on the examples above regarding total usage of these slots.

(using patricks example again with the image. that processor has 16 slots by default and the chipset shown 20. does this mean for that combination, you have 36 lanes to work with?)

im just mentally fatigued at this point and i just want to remove all doubt i was having on this subject for good, and hopefully anyone else who reads this.

 

[13thmonkey]

Yes and no, you have 16 + 20, 16 for the GPU and 20 for IO, unless the mobo specifically supports it some of the 20 cannot be used on GPU duties and the 16 cannot be used for IO. In reality it'll be the specific implementation on your MOBO that will define what you can and cannot do.

 

[Mochithecat]

ok. that settles that. thanks for the information monkey (that honestly sounds worse than i meant). i have other questions coming from that explanation, but the manuals should cover that hopefully.