M.2 add in card is 8x but only uses 4x?

[will0hlep]

I have this Asus Pcie gen 5 M.2 add in card from a previous build that turns a gen 5 PCIe 8x slot into a single gen 5 x4 m.2 Nvme slot.

 

My question is this:

looking at the traces it appears that only half the 8x connector is in use, does that mean this will work just as well with only 4 lanes as it does with 8?

 

also dumber question, but am I right in thinking that if I put this card in a gen 4 or 3 PCIe slot it will work but the drive will only run  at a max of gen 4 or 3 speeds?

[aDoomGuy]

Drive only uses PCIe x4 anyway so 4 more lanes would do nothing.

 

 

EDIT:

4 minutes ago, will0hlep said:

also dumber question, but am I right in thinking that if I put this card in a gen 4 or 3 PCIe slot it will work but the drive will only run  at a max of gen 4 or 3 speeds?

Yes. But since the drive is only 4x that would be the case regardless of the add in card being x4, x8 or x16.

 

So, if you put a gen 5 NVMe in that card on a gen 3 bus you get gen 3 x4. If you put a gen 3 NVMe on a gen 5 bus you also get gen 3 x4.

Will you notice the difference? Most probably not.

[PDifolco]

4 minutes ago, aDoomGuy said:

Drive only uses PCIe x4 anyway so 4 more lanes would do nothing.

That's weird, I have one PCie adapter for 1x M2 but it uses only a x4 slot

If this one can use x8/need a long slot I suppose it's designed to hold 2 drives !

[will0hlep]

3 minutes ago, PDifolco said:

That's weird, I have one PCie adapter for 1x M2 but it uses only a x4 slot

If this one can use x8/need a long slot I suppose it's designed to hold 2 drives !

I think that was their orginal plan and it would have made sense as the board it came with had a 16x slot running at 8x, but for some reason they decided to only put 1 m.2 slot on the card. very strange. Maybe they were worried about thermals. Apparently gen 5 SSDs are going to run very hot.

[PDifolco]

2 minutes ago, will0hlep said:

I think that was their orginal plan and it would have made sense as the board it came with had a 16x slot running at 8x, but for some reason they decided to only put 1 m.2 slot on the card. very strange. Maybe they were worried about thermals. Apparently gen 5 SSDs are going to run very hot.

Then just drop this thing and buy a x4 adapter to put in one bottom small PCie slot, they cost like 20 bucks

[aDoomGuy]

1 minute ago, PDifolco said:

That's weird, I have one PCie adapter for 1x M2 but it uses only a x4 slot

If this one can use x8/need a lon,g slot I suppose it's designed to hold 2 drives !

I don't think so. But I don't think I've seen a mobo with x4 slots in therms of physical propertes though. You got either your tiny ones or your full lenght ones, never seen any inbetweeny ones. If I understand correct my board have a x4 slot but it is x16 size in physical dimensions.

 

I got 3 long ones x16 and x8 and appears to be x4 for the last one. My small ones are x1 both. I got a add on card too for NVME and it is 4x.

3 minutes ago, will0hlep said:

I think that was their orginal plan and it would have made sense as the board it came with had a 16x slot running at 8x, but for some reason they decided to only put 1 m.2 slot on the card. very strange. Maybe they were worried about thermals. Apparently gen 5 SSDs are going to run very hot.

Could be. Or maybe they just had x8 cards laying around wondering what they could do with them?

I dunno. I've seen a card like that before, always found that strange.

[aDoomGuy]

1 minute ago, PDifolco said:

Then just drop this thing and buy a x4 adapter to put in one bottom small PCie slot, they cost like 20 bucks

His bottom one may be x4 slot in x16 dimension like on my board</guesswork>

[will0hlep]

6 minutes ago, PDifolco said:

Then just drop this thing and buy a x4 adapter to put in one bottom small PCie slot, they cost like 20 bucks

I don't actually have an immediate use for it, just realised I had it and wanted to assess it's usefulness for the future.

3 minutes ago, aDoomGuy said:

His bottom one may be x4 slot in x16 dimension like on my board</guesswork>

Given use cases like this it isn't really ewaste, it's just strangely designed...

[aDoomGuy]

1 minute ago, will0hlep said:

I don't actually have an immediate use for it, just realised I had it and wanted to assess it's usefulness for the future.

Given use cases like this it isn't really ewaste, it's just strangely designed...

Asus do work in mysterious ways sometimes, that's for sure.

[mariushm]

The card uses 4 lanes no matter what slot you plug it in. 

You can put it in x4 slot (if the slot has no wall at the end and no tall things to block the edge connector)

You can put it in x8 slot, you can put it in x8 slot. 

It will probably also work in x16 slots that have only 1 or 2 lanes (some B650 motherboards are made like that), in which case the M.2 connector will have only 1 or 2 pci-e lanes in it. 

 

They could have put TWO M.2 connectors and give each m.2 connector 4 pci-e lanes, but I suspect they didn't do it for a few reasons. 

Splitting 8 lanes into 2 groups of 4 requires bifurcation support in bios. No guarantee all the motherboards support that, and probably Asus didn't want to be stuck with guaranteeing all their motherboards will support bifurcation.

It's possible they didn't want RMA returns or warranty claims from people complaining about only one m.2 connector working when they plug the card into a slot that has only 4 lanes wired into it.

It's possible they wanted to bundle that card with some motherboards that only had 4 pci-e lanes available,  or maybe they planned to have a "Plus" / "Pro" version of same adapter with 2 m.2 connectors at a later time. 

 

One other thing is ... pci-e 5.0 is much more strict when it comes to signal quality, length of traces, even the circuit board material must be better. It's possible that by making the adapter x8 sized, the extra copper on the circuit board could improve the board even if it's not connected to anything.

Maybe they wanted the extra ground pads on the x4-x8 edge connector for that as well. 

 

[Blue4130]

11 hours ago, will0hlep said:

 

Given use cases like this it isn't really ewaste, it's just strangely designed...

Not really. It's smart design and business to reuse tooling and boards as much as possible. If they make an x8 sized adapter pcb, they can use it on x8 with dual m.2 AND single m.2 cards, if they made seperate x4 and x8 cards, they would neet to retool every time they wanted to make a batch or cards.