Question PCIEx16 drops to x 8 when M2 SSD is installed???

[Fakum]

I am looking to build a new PC with a 4090 GPU and an M2 ssd (and also considering it to support M2 Gen 5 for future upgrade). I am looking at the specs on a couple of Gigabyte boards and there are notes in there that I dont understand:

GIGABYTE Z790 AORUS Xtreme & GIGABYTE Z790 AORUS Master :

"1 x PCI Express x16 slot, supporting PCIe 5.0 and running at x16 (PCIEX16)
* The PCIEX16 slot shares bandwidth with the M2C_CPU connector. The PCIEX16 slot operates at up to x8 mode when a device is installed in the M2C_CPU connector.
* For optimum performance, if only one PCI Express graphics card is to be installed, be sure to install it in the PCIEX16 slot. "

Does this mean that if I install a 4090 into the PCIEx16 slot it drops down to x8 if I install an M2 SSD? Or is this typical for all boards anyway? How do I avoid any performance drops (If any) using these parts?

Thanks

 

[kschendel]

GIGABYTE Z790 AORUS Xtreme & GIGABYTE Z790 AORUS Master :

"1 x PCI Express x16 slot, supporting PCIe 5.0 and running at x16 (PCIEX16)
* The PCIEX16 slot shares bandwidth with the M2C_CPU connector. The PCIEX16 slot operates at up to x8 mode when a device is installed in the M2C_CPU connector.
* For optimum performance, if only one PCI Express graphics card is to be installed, be sure to install it in the PCIEX16 slot. "

Does this mean that if I install a 4090 into the PCIEx16 slot it drops down to x8 if I install an M2 SSD? Or is this typical for all boards anyway? How do I avoid any performance drops (If any) using these parts?

Yes, that's exactly what it means. Since the 4090 only runs at PCIe 4 anyway, if you use the M2C slot (which I think might be the top one, but double check the online manual), you'll be running the GPU at PCIe 4 x8 instead of x16. Will you notice? probably not.

How do you avoid performance drops? Don't use the M2C slot, use any of the others, preferably starting with M2A. If you want x16 on the GPU slot and a PCIe 5 SSD in M2C, tough. There's only so many PCIe lanes to work with, and in real life you're unlikely to notice anyway outside of benchmarking.

IMO the benefits of PCIe 5 for SSD's will be basically zero for 99.9999% of the user population anyway. If you are doing something that actually needs the full bandwidth to the GPU (unlikely!), just avoid the M2C slot.

 

[mv2devnull]

Will you notice? probably not.

This. Incidentally, I have GA-Z170X-?? and Intel i7-6700K. RTX 3070 for 3440x1440, and NVMe as PCIe card on the second x16 slot.
In other words, my GPU runs via PCIe 3.0 x8 and I don't know of anything better ...

 

[Fakum]

@blckgrffn , that is a very interesting alternate twist! I am going to ponder that for a bit, and while I do, I just want to try and clarify something. It seems that the Z790 Chipset motherboards may have similar characteristics after reading through all of this, and that is if you install your 4090 GPU in the PCIE 16 slot, and you install an M2 Gen 4 SSD in an M2 slot that is NOT shared with the PCIE 16 slot, all is well correct?

Now as to my initial post, if I later update the M2 SSD to a Gen 5 (in the future), thats when I will need to install it in the M2 slot that is rated for Gen5, and that slot would be shared with the GPU PCIE 16 slot and nocking the PCIE slot down to 8x. Now,,, if I read through this all correctly, I would NOT likely notice any performance difference in my DCS flight sim that I might actually notice?

 

[CP5670]

The AMD B650E boards have the same issue. This may actually be one benefit of X670E over B650E, they don't seem to have this limitation, although I'm not sure about the cheaper boards. I don't really care about Gen 5 NVME but do want to be able to use four drives without affecting the main PCIE slot.

 

[snoopy7548]

Like others said, it's only a concern if you have a Gen5 NVME, which 99.9% of people don't need. My Gigabyte Z790 Aorus Elite AX just has Gen4 NVME slots and doesn't have this problem.

Talking out of my @$$, for gaming you'd probably notice a difference between PCIe x8 vs x16 GPU performance over a Gen4 vs. Gen5 NVME...

The block diagram at the beginning of the manual tells you most of what you need to know in regards to NVME/PCIe/SATA port availability. They should put an asterisk with a note on this page so you don't have to dig through the manual, though.

Gigabyte Z790 Aorus Xtreme/Master




Gigabyte Z790 Aorus Elite AX

 

[CP5670]

Like others said, it's only a concern if you have a Gen5 NVME, which 99.9% of people don't need. My Gigabyte Z790 Aorus Elite AX just has Gen4 NVME slots and doesn't have this problem.

Talking out of my @$$, for gaming you'd probably notice a difference between PCIe x8 vs x16 GPU performance over a Gen4 vs. Gen5 NVME...

The block diagram at the beginning of the manual tells you most of what you need to know in regards to NVME/PCIe/SATA port availability. They should put an asterisk with a note on this page so you don't have to dig through the manual, though.

Gigabyte Z790 Aorus Xtreme/Master

For the boards I was looking at, it will drop down to PCIE 5 x8 for the main slot if you have four M.2 drives of any kind, not just Gen 5. So you can effectively only use three M.2 drives.

Are there any boards under $400 that support four drives without this limitation? The motherboard companies don't make this very clear, some of the X670E boards do it too.

 

[snoopy7548]

For the boards I was looking at, it will drop down to PCIE 5 x8 for the main slot if you have four M.2 drives of any kind, not just Gen 5. So you can effectively only use three M.2 drives.

Are there any boards under $400 that support four drives without this limitation? The motherboard companies don't make this very clear, some of the X670E boards do it too.

I don't see that listed anywhere. The manuals and block diagrams for the two boards you listed only show M2C sharing a PCIe x16 lane. The four other NVME slots are independent of that.

 

[blckgrffn]

I don't see that listed anywhere. The manuals and block diagrams for the two boards you listed only show M2C sharing a PCIe x16 lane. The four other NVME slots are independent of that.

Auros Elite AX just forgoes the PCIe 5 storage option and instead uses v4 lanes from the CPU and claims all the sata ports of 4x nvme drives are used. No imposed limitation on the x16 slot. That’s how I am reading that diagram.

 

[BoomerD]

The MSI Z690 Tomahawk DDR4 has no NVMe/PCI-e limitations, but, as posted above, offers 3 slots at Gen 4.0x4 and one slot at 3.0x4.

• M2_1 slot (From CPU)
  • Supports up to PCIe 4.0 x4
  • Supports 2242/ 2260/ 2280/ 22110 storage devices
• M2_2 slot (From Z690 chipset)
  • Supports up to PCIe 4.0 x4
  • Supports 2242/ 2260/ 2280 storage devices
• M2_3 slot (From Z690 chipset)
  • Supports up to PCIe 3.0 x4
  • Supports up to SATA 6Gb/s
  • Supports 2242/ 2260/ 2280 storage devices
• M2_4 slot (From Z690 chipset)
  • Supports up to PCIe 4.0 x4
  • Supports up to SATA 6Gb/s
  • Supports 2242/ 2260/ 2280 storage devices

The thing that causes the reduction in speed is PCI-e 5.0 and M.2 NVMe 5.0. If your board only supports gen 4.0 NVMe drives, then the PCI-e 5.0 slot isn't affected.

 

[CP5670]

I don't see that listed anywhere. The manuals and block diagrams for the two boards you listed only show M2C sharing a PCIe x16 lane. The four other NVME slots are independent of that.

I'm not the OP, but was seeing this issue with many of the AMD B650E/X670E boards. Look at this board for example. The comments suggest that filling one of the M.2 slots with anything (even M.2 Gen 3 or 4) drops the PCIE 5 slot down to 8x.

 

[igor_kavinski]

Don't worry. Intel will fix this "issue" in Z890. Like they always do.

Futureproofing is never their concern. Future sales are.

 

[Fakum]

I appreciate the feedback guys, I really do! I dont really understand quite a few things discussed here except maybe some of the comments, I'm not really familiar with interpreting those block diagrams and some of meanings of some of other things, but what I have seemed to have surmised is that, I was initially looking to do a new build that would get me through the next 6 years (typical for me) and taking advantage of the GEN 5 SSD data transfer rates in the future. Again, I am primarily a DCS Combat Flight simmer, and I am very familiar with how the storage devices have impacted this Sim over the years. My interpretation of what I have read here so far leads me to believe that I shouldn't concern myself with a GEN 5 motherboard at this time, especially if there is a premium for that feature. Perhaps I should just look for a KickA$$ GEN 4 gaming motherboard instead.

 

[blckgrffn]

I appreciate the feedback guys, I really do! I dont really understand quite a few things discussed here except maybe some of the comments, I'm not really familiar with interpreting those block diagrams and some of meanings of some of other things, but what I have seemed to have surmised is that, I was initially looking to do a new build that would get me through the next 6 years (typical for me) and taking advantage of the GEN 5 SSD data transfer rates in the future. Again, I am primarily a DCS Combat Flight simmer, and I am very familiar with how the storage devices have impacted this Sim over the years. My interpretation of what I have read here so far leads me to believe that I shouldn't concern myself with a GEN 5 motherboard at this time, especially if there is a premium for that feature. Perhaps I should just look for a KickA$$ GEN 4 gaming motherboard instead.

A good nvme 4 drive will already be 10x faster than your SATA drive, and for me when you hit an order of magnitude higher potential speed difference on storage, that is a solid time to upgrade. I have been moving everything possible to pure nvme storage I light of the bottom falling out of the flash storage market.

 

[Fakum]

Yeah, one of the things I tried to do with this current build was to install an M2 drive when I needed to update my storage capacity, didnt work out well on this build for reasons I cant remember entirely. One of the main reasons was that I do backups often using Acronis (Which has served me flawlessly for countless year) for some reason, after I migrated and attempted a backup, it was slow as anything as I recall. Ether way, I didnt look back to try and do it again on this rig.

 

[Fakum]

I'm not the OP, but was seeing this issue with many of the AMD B650E/X670E boards. Look at this board for example. The comments suggest that filling one of the M.2 slots with anything (even M.2 Gen 3 or 4) drops the PCIE 5 slot down to 8x.

I am seeing that as well,,, not sure if it applies to most or not? I started thinking more seriously about an AMD option, this didnt help my brain at all LOL

 

[BonzaiDuck]

BestBuy on ebay has an HP Victus 15L tower in white black, with an i3-12100 and a GTX 1650 4GB, brand new, for $599.

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Sorry, that was a note for BonzaiDuck. I'll PM him too.

[Also for Igor] With my focus on my bed-bound Moms, yes -- I'm really keen at the moment for money-management, business e-mail, my spreadsheets, etc. The simulation games -- gran prix and stock car or fright stimulators are still up and running, but nothing that needs more hardware than I now have.

So, Larry, I'll give that HP a look-see. I'm in no hurry. These old quad-core Sky and Kaby systems are still rocking fine for me. Heck. I've finally decided to resurrect an old i7-2700K system and HTPC. I'll download Media Portal today so I can f*** around with it before the Sony X85K 43" arrives Friday. [My inquiries about TVs are on that thread, and I think igor responded with good intel.]

 

[Fakum]

What the heck is up with that????

 

[In2Photos]

This is the first generation of motherboards that support PCIe 5. So there's going to be limitations. You just have to decide what's most important. Have you seen the first few releases of Gen 5 NVME drives? Not much going for them. Glad I decided not to wait for them. I'm satisfied with my Gen 4 drives and my motherboard, while limited to 3 Gen 4 NVME drives, doesn't have any other restrictions in regards to PCIe lanes when using NVME drives.

Maybe there will be something like this ASRock board with an NVME expansion card that essentially added an additional chipset in the future.

 

[Fakum]

Yeah, after all of this research, I'm going to drop back and punt. Im not that interested in GEN 5 at this point or DDR 5 memory either. Going to look into Gen 4 hardware and AMD options as well. Thanks

 

[Fakum]

After extensive reading, I decided to go with the AMD 7800X3D (Purchased yesterday). Main reason why I went with AMD 7800X3D vs Intel Core i9-13900K. Heat, Watts & Gaming performance comparisons. I also have no need to concern myself with Gen 5 concerns for the near future based on most of what I have read so far. I cant count how many videos I have watched along with reading articles. I appreciate the knowledgeable feedback I have received here and will continue to post up with questions. Now the next journey begins. Selection of motherboard, then its RAM. By the way, I found what I believe to be the best informative video regarding AMD MOBO selections. This really cleared up alot of confusion for me.

So far my list for MOBOs are as follows, the ones with strike through's have been omitted due to some lack of features, such as lack of full audio suite on back Panel and small amount of Rear USB ports or cost.

 

[blckgrffn]

Congrats!

FWIW, I wouldn't consider an ASUS personally, because of bad experiences with them and their Armory Crate software. Really bad.

Everyone has horror stories for every brand, and while I really, really like the ASUS fan tuning wizards, everything else I have had middling to worse experience with.

I've had one or two bad boards from everyone else (hey Epox! ) but none so "don't worry, we know better than you" than the vibe I get from ASUS.

 

[WelshBloke]

Congrats!

FWIW, I wouldn't consider an ASUS personally, because of bad experiences with them and their Armory Crate software. Really bad.

Everyone has horror stories for every brand, and while I really, really like the ASUS fan tuning wizards, everything else I have had middling to worse experience with.

I've had one or two bad boards from everyone else (hey Epox! ) but none so "don't worry, we know better than you" than the vibe I get from ASUS.

Asus hardware is pretty solid, I'd light myself on fire before installing any of their software though! Luckily you don't need any of that stuff, you can do it all in the BIOS.

 

[blckgrffn]

Asus hardware is pretty solid, I'd light myself on fire before installing any of their software though! Luckily you don't need any of that stuff, you can do it all in the BIOS.

Some of their boards will try to auto install after a windows install, so you have to watch out for it. Most of their boards also allow you to disable this in the bios - but I’ve heard some don’t.

In any case, yeah. The “value added” software that accompanies these boards can vary from a little useful but glitchy to full on malware :/

Heaven forbid you want to configure RGB stuff in Windows! You’re gonna need this 1GB software package that runs seven services to do that 😂

 

[Fakum]

Thanks for the tips, especially for the software install stuff.

 

[CP5670]

I ended up getting a X670E Tomahawk board, which has one shared M.2/PCIE slot like this. I can see a clear reduction in SSD speeds in that slot (with Crystal Disk Mark) even with a gen 3 SSD, to about half of what they should be. I normally prefer to have my sound card in that slot because it leaves more room for the video card fans to intake air, but had to move the card up. It's a nice board otherwise and reasonably priced for X670E.

I was also reading that many of the Asus boards have limitations like this on the SATA ports, both B650E and X670E ones.