I want to understand PCI-E lanes?

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MPDota

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So i was watching numerous of explanatory videos and read bunch of threads about this, but i'm still confused.

So what confuses me the most:

What is connected through motherboard with these lanes? GPU, and what else? Sata (HDD/SSD), something else? Everything?

What does the number of PCIE lanes that CPU use mean(28/40)? Aren't PCIE lanes there to connect stuff to the CPU?

Is x1 basic measurement of PCIE lane width, and then x2,x4,x8,x16 are just multiplication of that x1?

Why do some peole worry about how many lanes GPU and CPU use so they have enough, are GPU and CPU using same lanes?

Thanks if someone can answer me these question.
 
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Some PCIe lanes connect directly to the CPU. Most modern mainstream CPUs have 16 direct PCIe 3.0 lanes. The rest of the lanes are routed through a PCIe switch on the motherboard that's part of the chipset. GPUs, wifi cards, sound cards, NVMe SSDs are all connected via PCIe. SATA drives aren't technically connected though PCIe, but the I/O is structured with Intel chipsets means that SATA connections are more or less treated as PCIe 3.0 x1 connections.

You always want your GPU to use CPU lanes direct to the CPU if possible (and SLI only works with direct-CPU lanes, AFAIK). People want their GPU to have as much bandwidth as possible, so for multi GPU systems people might get high end CPUs that have enough lanes for two GPUs to have x16...
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TJ Hooker

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Some PCIe lanes connect directly to the CPU. Most modern mainstream CPUs have 16 direct PCIe 3.0 lanes. The rest of the lanes are routed through a PCIe switch on the motherboard that's part of the chipset. GPUs, wifi cards, sound cards, NVMe SSDs are all connected via PCIe. SATA drives aren't technically connected though PCIe, but the I/O is structured with Intel chipsets means that SATA connections are more or less treated as PCIe 3.0 x1 connections.

You always want your GPU to use CPU lanes direct to the CPU if possible (and SLI only works with direct-CPU lanes, AFAIK). People want their GPU to have as much bandwidth as possible, so for multi GPU systems people might get high end CPUs that have enough lanes for two GPUs to have x16 (or 3-4 GPUs to have 8 lanes each).

When you see "PCIe x[#]", that number can be referring to slot size or bandwidth ("physical" or "electrical", respectively). As far as bandwidth goes, yes, PCIe x4 would be four times the bandwidth as x1, etc. For slot size, I don't thing PCIe x4 is exactly four times as big as x1, but size goes up. Also, you can a slot that is physically x16, but offers less bandwidth (only x8, x4, or x1 electrically).
 
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MPDota

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Oh thanks for answers.

So what i still get:

All lanes are coming to every connected component and back to CPU?

So if you have 2x GPUS that need x16 bandwidth you can't use (28) PCIE "laned" CPU because there is not enough width for all that information? Because 2*x16 is 32?
 
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