Question Need help with PCIe speeds

[Joe1234564215]

So, my motherboard is asus z87-k, I'm thinking about modding the bios, buying an adapter and the samsung 970 evo. However, according to my mb specs:

The 1st pcie slot is taken by my gpu, the 2nd one supposedly runs at pcie 2.0 X16 (Idk why there's X4 mode written in the brackets, what does that mean?). According to 970 evo, it says it needs pcie 3.0 X4, and I've heard that X16 runs 4 times faster than X4, but also 2.0 is slower than 3.0. So if my pcie 2.0 slot works at X16 and not X4 (idk which one it is), would it be fast enough like the required pcie 3.0 X4 slot to be able to get the full 3400 mb/s write and 1500 mb/s read speed that's advertised? Also what kind of adapter exactly do I need? Like I know it's m2 to pcie but I don't know what else to search for

 

[Math Geek]

pcie 3.0 x4 = 2.0 x8 since a 3.0 lane is twice as fast a 2.0 one which is twice as fast as a 1.0 lane.

the first pcie slot will run at full x16 speed if it is the only slot used. once the second slot is used like you are planning to do, then both slots use less lanes. normally x8 and x8. this would be more than enough for both cards to run full speed. though you're not likely to see the full advertised speeds of the m2 card anyway. honestly a SATA SSD gives up very little real world performance over the more expensive m.2 drives. and once you use the adapter it slows things down anyway. save yourself a lot of trouble and get a good quality SATA SSD and be done with it.

the manual is not very specific about the x4 mode so not sure what it takes to put it into that mode. likely has to do with lane sharing if other features are used but it does not go into what exactly it moves where. most likely the 2nd pcie x16 slot would go from x8 (if both x16 slots are being used) to x4 if you use something like sata express or the m.2 slot or extra SATA ports or other combo like that. you're mobo lacks a lot of those features so it is most likely that those 2 sata ports off to the side and separate from the 4 grouped bottom of the mobo would take 4 lanes from that second slot if you used them. again manual does not specify this but i have seen this on many other boards.

most motherboard's have more features than lanes to supply them. so there is always a trade off when chosing what to use and often you can't mix certain features since they both need the same lanes. the manual usually details how the lanes are divided up and in what scenario. high end (read expensive) boards can add an extra chip to the board that creates and can handle more lanes but that is usually only seen on top end boards that cost extra.

 

[TJ Hooker]

For the 2nd slot, it says PCIe x16 because that's the physical size/length of the slot. However, it is only electrically wired for x4 bandwidth. So it would provide PCIe 2.0 x4 bandwidth, which is half of the max bandwidth of a PCIe 3.0 x4 connection.

The SSD would work in that slot as PCIe is forward/backward compatible, but would not have it's full bandwidth. There is no way for you to run it at full bandwidth without removing your GPU, even if you get an adapter.

Why not just get a SATA SSD? That board might not even support booting from an NVMe drive. The differences between SATA and NVMe aren't really noticeable most of the time anyway.

 

[USAFRet]

The choice between NVMe vs SATA SSD relies on 2 things:

Your motherboard capabilities and your use case.

Your motherboard is a strike against a 970 EVO or similar. It will never run at its full speed, and be just barely faster than a SATA III drive. (but for twice the price)
If your use case of the drive (large video production, maybe) would be noticeable with the difference, you would have moved off that Z87 motherboard long ago.

We've seen many people in here who have made this switch, and seen not a whole lot of user facing benefit. Even on newer boards that will run that drive at its full speed.
The jump from HDD to SSD was huge.
From SATA SSD to NVMe SSD, not so much.

Just because a thing exists, does not mean it is useful in all situations.