Questions about M.2 SSDs and using them in PCIe slots

[ExclamationMark]

Hey everyone,

So I'm going to be creating a new PC build soon (motherboard will be the Gigabyte GA-Z170-Gaming K3, in case that will make any difference). I initially was going to be using a 256GB Samsung 850 EVO as my primary drive (OS, main programs and all that), until I heard all this talk about M.2 SSDs. I was "out of the loop" for quite some time, so I only heard about them recently. Got me interested and now I've decided I'm going to go for one. Specifically an SM951. I will be installing it in a PCIe slot using an adapter (Lycom DT-120), but I have some questions:
1. there are 2 types of SM951 - one using AHCI as its controller, the other NVMe. I've never heard of these before - what's the difference? From what I could tell, AHCI was developed ~10 years ago as a HDD only controller, but was later modified to control SSDs too. The NVMe was then created for SSDs only? I'm not sure if I have any of that right, but it's what I heard from watching multiple YouTube videos.
2. also while watching YouTube videos, I remember something about how the SSD will be halving the "lanes" the GPU can use to 8, or something like that? What is that all about? Will it somehow lower GPU performance or do I have it all wrong again?

Thanks in advance guys!

 

[wildcard1978]

Nvme is new type of standardize ssd controller and only supports full uefi boot and uefi installs if windows
You motherboard bios has to support nvme or have a updated bios that adds nvme support to use a nvme ssd

On the pics express lanes yes in some cases when a board does have enough PCI express lanes specially when running sli it can knock down the bus sped from x16 to x8 for one of the cards or sometimes both . Like my asrock 990 fx board supports x16 mode for both cards in sli but still has enough lanes to run a m.2 ssd or PCI express ssd with no bus speed loss

 

[wildcard1978]

And a m.2 ssd in and adapter would be same as any pics express ssd PCI express ssd can knock down the bus in certain cases