PCI Express Slot differences

[Drizzt5]

Hello,

I just purchased a B550m motherboard and installed all the hardware. It works at the moment, but I want to make sure I am getting all the performance I can and seeing if there are any features I overlooked.

There are 3 PCIE slots:


While flipping through the manual I noticed that the 3rd slot, while being PCIe 3.0 x16, says it is used for x4 lane width graphics cards.

I currently have my graphics card in that slot and left the PCIe 4.0 slot with x16 lane width open for four reasons.
1. My GPU would bump up against a fan on the case for rear exhaust. Removing it would hurt airflow out the back.
2. My GPU is directly under some case side fans in the 3rd slot
3. I was going to save that slot for an SSD eventually that can take advantage of PCIe 4.0
4. I was under the impression there was no real world performance gain for current GPUs to take advantage of the bandwidth difference between 3.0 and 4.0.


However...as you can see from the image attached. The first slot says x16 lane and the 3rd says x4 lane. Could someone explain what that means? Would this noticeably impact performance? I'm worried this might be a face palm moment.

 

[TheLostSwede]

Only the first slot is directly connected to the CPU, the other slots on your board goes via the chipset.
Right now, you're getting something like half the bandwidth your GPU needs and quarter of what it can get, which results in poor performance.
On top of that, you're now sharing bandwidth with the SATA ports and all other peripherals connected via the chipset, so you might actually have less than four lanes worth of PCIe bandwidth for your graphics card.

The SSD should go in the first M.2 slot, not in the PCIe x16 slot. This way, the SSD doesn't have to share bandwidth with other devices, as that M.2 slot is also connected directly to the CPU.

You're correct that most graphics cards won't see any performance gain from a PCIe 4.0 slot, as most graphics cards today are PCIe 3.0. There's also not much difference in going from 16 lanes to eight lanes of PCIe, but going to four lanes, is not a good idea.

In short, you're pretty much running your graphics card in a PCIe 1.0 x16 slot with what you've done (the actual bandwidth is actually a tad less than that even).

You can read a bit more about it below, although this is obviously for a much faster card than you own.

NVIDIA GeForce RTX 2080 Ti PCI-Express Scaling

It takes a lot of bandwidth to support the fastest graphics card, especially one that can play anything at 4K 60 Hz, with an eye on 120 Hz. The GeForce RTX 2080 Ti could be the most bandwidth-heavy non-storage PCIe device ever built. PCI-Express gen 3.0 is facing its design limits.

www.techpowerup.com

Here's an older one that might be more comparable to your card. As you can see, going via the chipset, even if the bandwidth for the slot is the same, you lose some extra performance.

NVIDIA GeForce GTX 1080 PCI-Express Scaling

In this article, we investigate how performance of NVIDIA's GeForce GTX 1080 is affected when running on constrained PCI-Express bus widths such as x8 or x4. We also test all PCIe speed settings, 1.1, 2.0, and 3.0. One additional test checks on how much performance is lost when using the...

www.techpowerup.com

 

[Drizzt5]

Only the first slot is directly connected to the CPU, the other slots on your board goes via the chipset.
Right now, you're getting something like half the bandwidth your GPU needs and quarter of what it can get, which results in poor performance.
On top of that, you're now sharing bandwidth with the SATA ports and all other peripherals connected via the chipset, so you might actually have less than four lanes worth of PCIe bandwidth for your graphics card.

The SSD should go in the first M.2 slot, not in the PCIe x16 slot. This way, the SSD doesn't have to share bandwidth with other devices, as that M.2 slot is also connected directly to the CPU.

You're correct that most graphics cards won't see any performance gain from a PCIe 4.0 slot, as most graphics cards today are PCIe 3.0. There's also not much difference in going from 16 lanes to eight lanes of PCIe, but going to four lanes, is not a good idea.

In short, you're pretty much running your graphics card in a PCIe 1.0 x16 slot with what you've done (the actual bandwidth is actually a tad less than that even).

You can read a bit more about it below, although this is obviously for a much faster card than you own.

NVIDIA GeForce RTX 2080 Ti PCI-Express Scaling

It takes a lot of bandwidth to support the fastest graphics card, especially one that can play anything at 4K 60 Hz, with an eye on 120 Hz. The GeForce RTX 2080 Ti could be the most bandwidth-heavy non-storage PCIe device ever built. PCI-Express gen 3.0 is facing its design limits.

www.techpowerup.com

Here's an older one that might be more comparable to your card. As you can see, going via the chipset, even if the bandwidth for the slot is the same, you lose some extra performance.

NVIDIA GeForce GTX 1080 PCI-Express Scaling

In this article, we investigate how performance of NVIDIA's GeForce GTX 1080 is affected when running on constrained PCI-Express bus widths such as x8 or x4. We also test all PCIe speed settings, 1.1, 2.0, and 3.0. One additional test checks on how much performance is lost when using the...

www.techpowerup.com

Thank you. I just removed the fan and put the card in that slot instead. I did not realize it was x4 when I put it in. I wrongly assumed it was x16 but PCIe 3.0.

I will test and hopefully performance is great now!

 

[TheLostSwede]

Thank you. I just removed the fan and put the card in that slot instead. I did not realize it was x4 when I put it in. I wrongly assumed it was x16 but PCIe 3.0.

I will test and hopefully performance is great now!

Time to get a slimline fan?

 

[dorsetknob]

PCIx16 Slots come in 3 flavors
all are physical identical they differ Electricaly.
1. PCIx16 = full 16 lanes
2. PCIx16 = 8 electrical connected lanes.
3. PCIx16 = 4 electrical connected lanes.
How many lanes each Slot has Depends on MotherBoard and chip/chipset manafacture's implemtation

 

[Drizzt5]

Time to get a slimline fan?

Eventually (probably Christmas) I will be putting all of this in a smaller micro atx case (currently mid tower), so I'll just figure out how to put the fan on the outside of the case with a grill for now.

I'm trying to make do salvaging from parts I have laying around and I have a lot of fans and grills.

Thank you for explaining to me the differences everyone.

I'm glad I flipped through the manual and asked

edit:

Btw, I think this was related to the problems I was experiencing in this thread:

New Build Issue - Slow CPU while in game

I have not used the latency monitor, but could those issues be related on some interrupt issue so system halts occasionally? Check also task manager if there is some program consuming CPU power (not sure if interrupt problems can be seen there). I had strange problems with my old i7 3930K...

www.techpowerup.com

Hopefully my error helps people in the future! If you are experiencing weird stutters, check your PCIe slots in the motherboard manual... whoops

 

[TheLostSwede]

Eventually (probably Christmas) I will be putting all of this in a smaller micro atx case (currently mid tower), so I'll just figure out how to put the fan on the outside of the case with a grill for now.

I'm trying to make do salvaging from parts I have laying around and I have a lot of fans and grills.

Thank you for explaining to me the differences everyone.

I'm glad I flipped through the manual and asked

edit:

Btw, I think this was related to the problems I was experiencing in this thread:

New Build Issue - Slow CPU while in game

I have not used the latency monitor, but could those issues be related on some interrupt issue so system halts occasionally? Check also task manager if there is some program consuming CPU power (not sure if interrupt problems can be seen there). I had strange problems with my old i7 3930K...

www.techpowerup.com

Hopefully my error helps people in the future! If you are experiencing weird stutters, check your PCIe slots in the motherboard manual... whoops

You live and you hopefully learn from mistakes like this.

 

[bonehead123]

Only the first slot is directly connected to the CPU, the other slots on your board goes via the chipset.
Right now, you're getting something like half the bandwidth your GPU needs and quarter of what it can get, which results in poor performance.
On top of that, you're now sharing bandwidth with the SATA ports and all other peripherals connected via the chipset, so you might actually have less than four lanes worth of PCIe bandwidth for your graphics card.

The SSD should go in the first M.2 slot, not in the PCIe x16 slot. This way, the SSD doesn't have to share bandwidth with other devices, as that M.2 slot is also connected directly to the CPU.

You're correct that most graphics cards won't see any performance gain from a PCIe 4.0 slot, as most graphics cards today are PCIe 3.0. There's also not much difference in going from 16 lanes to eight lanes of PCIe, but going to four lanes, is not a good idea.

In short, you're pretty much running your graphics card in a PCIe 1.0 x16 slot with what you've done (the actual bandwidth is actually a tad less than that even).

You can read a bit more about it below, although this is obviously for a much faster card than you own.

NVIDIA GeForce RTX 2080 Ti PCI-Express Scaling

It takes a lot of bandwidth to support the fastest graphics card, especially one that can play anything at 4K 60 Hz, with an eye on 120 Hz. The GeForce RTX 2080 Ti could be the most bandwidth-heavy non-storage PCIe device ever built. PCI-Express gen 3.0 is facing its design limits.

www.techpowerup.com

Here's an older one that might be more comparable to your card. As you can see, going via the chipset, even if the bandwidth for the slot is the same, you lose some extra performance.

NVIDIA GeForce GTX 1080 PCI-Express Scaling

In this article, we investigate how performance of NVIDIA's GeForce GTX 1080 is affected when running on constrained PCI-Express bus widths such as x8 or x4. We also test all PCIe speed settings, 1.1, 2.0, and 3.0. One additional test checks on how much performance is lost when using the...

www.techpowerup.com

Maybe we could get the mods to make this a sticky so it stays at the top of the respective page ???

 

[EarthDog]

Maybe we could get the mods to make this a sticky so it stays at the top of the respective page ???

instead, how about it just says "RTFM"... seriously...it's all there.

12 years and hundreds of posts and we dont know where to properly install things according to the manual? Zoinks!

Edit: Bonehead, stick to trashing/hating on new products...

 

[Drizzt5]

instead, how about it just says "RTFM"... seriously...it's all there.

12 years and hundreds of posts and we dont know where to properly put things according to the manual? Zones!

I think this is a bit mean spirited. I looked at the manual and missed that it was a x4 lane. I thought it was PCIe 3 vs 4. So my mistake, true. I later looked back at the manual and asked my question here just to get some more information from kind experts (I've been gone from this site and PC building for 9 years). I can share my userbenchmark score and other tests I've done if you like, the performance difference is actually negligible.

The errors i experienced however were noticeable. Stuttering in chrome and such. It looked like a driver issue.

So yes, live and learn. But no reason to mock me.

 

[EarthDog]

I think this is a bit mean spirited. I looked at the manual and missed that it was a x4 lane. I thought it was PCIe 3 vs 4. So my mistake, true. I later looked back at the manual and asked my question here just to get some more information from kind experts (I've been gone from this site and PC building for 9 years). I can share my userbenchmark score and other tests I've done if you like, the performance difference is actually negligible.

The errors i experienced however were noticeable. Stuttering in chrome and such. It looked like a driver issue.

So yes, live and learn. But no reason to mock me.

Relax, drizz... it was more in reference to making this(that post) a sticky than it was to any shortcomings of yours. Mistakes happen, indeed....it just so happens that the information is in the manual, hence my comment.

 

[Drizzt5]

Relax, drizz... it was more in reference to making this(that post) a sticky than it was to any shortcomings of yours. Mistakes happen, indeed....it just so happens that the information is in the manual, hence my comment.

I literally shared a picture of all the manual had to say on the matter and asked for more information. It was provided and I am grateful.

The part of your comment you deleted about 12 years and such was not very friendly. But cheers.

 

[EarthDog]

The part of your comment you deleted

That would be the staff who deleted it... likely due to a report.

Apologies. My expectations are high of long time users... still no excuse (for me to say that).

 

[95Viper]

This thread seems to have gone off topic to just being insulting.
This thread is closed...

Have A Nice Day