NVMe PCIe x4 SSD on M.2 PCIe x2 slot?

Question

i'm about to get a new SSD for my PC, and before spending the money i have some doubts about my decision i would like to clarify

First, my mobo is a B450 Aorus Pro Wifi, it has 2 M.2 slots, one of them full length (22110) compatible with PCIe 3.0 x4 and the other one standard length (2280) and support only for PCIe 3.0 x2

About the drive, i'm aiming for a 1tb XPG SX8200 Pro , which is a PCIe 3.0x4 SSD

My first M.2 slot is already taken by the main SSD, which i use for the OS and other stuff, i can't really use it. Will a PCIe x4 SSD work on a PCIe x2 slot? How much performance will be lost if it does? Will it be worth it?

Solution

A single lane of PCIe 3.0 is capable of, in theory, 985MB/s. Two lanes would be twice that at 1970MB/s.

Overheads may eat into that slightly.

PCIe should also negotiate how many lanes are available, so if only two are available then both sides should fall down to using two lanes. It should work fine. An x4 SSD might be able to theoretically reach up to 3940MB/s, but in practice many of them are closer to 2-3GB/s and whether or not you can actually make use of that bandwidth is down to the program itself.

Okay it will be slower than being in an x4 slot, but probably not noticeably so. It will still be far faster than a SATA SSD by nearly 4 times, and an order of magnitude faster than an old HDD.

Comments

[cst1992]

To add to this answer(for new users): you can install said SSD even in older interfaces. My M.2 slot is PCIe 2.0 x2 and it has a 970 Evo SSD, which can reach speeds of 3,500 MB/s. However, the drive only reaches a maximum of 820 MB/s due to the limiting interface. If my interface were 3.0 x2 then it should have been able to reach (maybe) 1700 MB/s.