Something I've noticed with new Intel motherboards/chipsets

BrianInEngland · Jan 28, 2023

I've been looking at a potential new build, likely AMD X670E. These boards are well-specced. I already use X570 and like the look/features of the new boards.

Out of interest and to compare I've looked at Intel Z790 boards. With every one I've looked at (two 'high end' from both Gigabyte and MSI) I've noticed that using the Gen 5 M.2 drive slot reduces the PCI-E x16 GPU slot to x8 speed.

AMD boards can run both x16 PCI-E Gen 5 and an M.2 Gen 5, with Intel it seems to be either/or.

I can't say that they're all like that. The Z790 can run faster RAM but does seem strange that the top of the line boards are PCI lane limited in this way.

Not intended as an argument which platform is better, it was just an observation.

Dru2 · Jan 28, 2023

BrianInEngland said:
BrianInEngland said:

I've been looking at a potential new build, likely AMD X670E. These boards are well-specced. I already use X570 and like the look/features of the new boards.

Out of interest and to compare I've looked at Intel Z790 boards. With every one I've looked at (two 'high end' from both Gigabyte and MSI) I've noticed that using the Gen 5 M.2 drive slot reduces the PCI-E x16 GPU slot to x8 speed.

AMD boards can run both x16 PCI-E Gen 5 and an M.2 Gen 5, with Intel it seems to be either/or.

I can't say that they're all like that. The Z790 can run faster RAM but does seem strange that the top of the line boards are PCI lane limited in this way.

Not intended as an argument which platform is better, it was just an observation.

Click to expand...

I've been looking at a potential new build, likely AMD X670E. These boards are well-specced. I already use X570 and like the look/features of the new boards.

Out of interest and to compare I've looked at Intel Z790 boards. With every one I've looked at (two 'high end' from both Gigabyte and MSI) I've noticed that using the Gen 5 M.2 drive slot reduces the PCI-E x16 GPU slot to x8 speed.

AMD boards can run both x16 PCI-E Gen 5 and an M.2 Gen 5, with Intel it seems to be either/or.

I can't say that they're all like that. The Z790 can run faster RAM but does seem strange that the top of the line boards are PCI lane limited in this way.

Not intended as an argument which platform is better, it was just an observation.

You might want to look to the actual instructions of the boards. Example this Gigabyte Z790 Elite AX board. Page 9 - Expansions slots...

1 x PCI Express x16 slot, supporting PCIe 5.0 and running at x16 (PCIEX16) * For optimum performance, if only one PCI Express graphics card is to be installed, be sure to install it in the PCIEX16 slot

Source: https://download.gigabyte.com/FileL...221118.pdf?v=672a72e0a0eed6a8be6ff24ef4d196fb (PDF).

It also depends on M.2 slot used as noted on page 8 in the manual for the Gigabyte Z790 Aorus Master as noted here...

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.

Source: https://download.gigabyte.com/FileL...221121.pdf?v=fc616ddb252426d9174edf3b869281ef (PDF)

If you don't use that slot, you'll still get x16

BrianInEngland · Jan 28, 2023

Dru2 said:
You might want to look to the actual instructions of the boards. Example this Gigabyte Z790 Elite AX board. Page 9 - Expansions slots...

Source: https://download.gigabyte.com/FileL...221118.pdf?v=672a72e0a0eed6a8be6ff24ef4d196fb (PDF).

The is no either or in that statement

The ones I saw did, like with an MSI one it says if the gen 5 M2 slot is used, the PCI x16 slot runs at x8, same with the Xtreme Gigabyte boards. Perhaps the example you give is the exception rather than the rule.

Dru2 · Jan 28, 2023

BrianInEngland said:
Perhaps the example you give is the exception rather than the rule.

I doubt it. As noted, you need to read the fine print

BrianInEngland said:
The ones I saw did, like with an MSI one it says if the gen 5 M2 slot is used, the PCI x16 slot runs at x8, same with the Xtreme Gigabyte boards.

Yeah, like everything else, there's always a "depends". Here it's about the board itself.

And I'll have to look at the extreme cause I doubt that's the case there.

Edit: No issue with the Aorus Z790 Xtreme board...

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

Source: https://download.gigabyte.com/FileL...221011.pdf?v=1f59eac1aabec0b72fe03db1e403967f (page 8) (PDF)

Dru2 · Jan 28, 2023

For clarity, I'm not here to debate which platform is better, I'm merely pointing out the error of the OP's post.

With that I'll move on as to not be a part of a flame war that may arise.

Peace

bobkn · Jan 29, 2023

A question I haven't seen the answer to yet:

A Gen12 or 13 Intel CPU supports 16 PCI-E 5.0 lanes. If a PCI-E 5.0 slot is populated, the GPU slot drops back to X8.

The M.2 slot uses 4 lanes.

Is there a reason that a second PCI-E 5.0 slot that uses the remaining 4 lanes isn't provided?

BrianInEngland · Jan 29, 2023

Dru2 said:
For clarity, I'm not here to debate which platform is better, I'm merely pointing out the error of the OP's post.

With that I'll move on as to not be a part of a flame war that may arise.

Peace

This is from the MSI Z790 Godlike (their top-tier board). Note what it says about the x16 slot if an M2 drive is used in the ONLY gen 5 slot:

In fact the other PCI-E slot is unavailable as well when using the gen 5 SSD slot

Dru2 · Jan 29, 2023

BrianInEngland said:
This is from the MSI Z790 Godlike (their top-tier board). Note what it says about the x16 slot if an M2 drive is used in the ONLY gen 5 slot:

In fact the other PCI-E slot is unavailable as well when using the gen 5 SSD slot

Can't speak for MSI. As I've only been with Gigabyte since 2010, with my current board being an Aorus Z390 Xtreme as seen in my system specs. That said, I'd really be surprised if that MSI premium board actually had the limitation you say. Perhaps a link to the board you're talking about would help?

BrianInEngland · Jan 29, 2023

Dru2 said:
Can't speak for MSI. As I've only been with Gigabyte since 2010, with my current board being an Aorus Z390 Xtreme as seen in my system specs. That said, I'd really be surprised if that MSI premium board actually had the limitation you say. Perhaps a link to the board you're talking about would help?

The manual is available here

MSI MEG Z790 GODLIKE, E-ATX - Intel 13th/12th Gen - 26+2 Phases, DDR5, PCIe 5.0, 10G LAN, Wi-Fi 6E

Featuring the latest technology, high-speed transmission, ultra-performance, and industry's first M-Vision Dashboard, the MEG Z790 GODLIKE is developed to unleash the extreme gaming potential of the Intel 13th gen processors.

uk.msi.com

Attached pics are from the Gigabyte Z790 Xtreme manual, same limitation (the M2C_CPU connector is the only Gen 5 NVMe slot)

Dru2 · Jan 29, 2023

BrianInEngland said:
This is from the MSI Z790 Godlike (their top-tier board). Note what it says about the x16 slot if an M2 drive is used in the ONLY gen 5 slot:

In fact the other PCI-E slot is unavailable as well when using the gen 5 SSD slot

It again, appears you've misunderstood what you're looking at. READ the manual instead of being confused by a diagram...

∙ 2x PCIe x16 slots (From CPU) • Supports x16/x0, x8/x8 • PCI_E1 supports up to PCIe 5.0 x16* • PCI_E2 supports up to PCIe 5.0 x8** * PCI_E1 slot will run at x8 speed with when installing device in the PCI_E2 slot or M2_4 slot. ** PCI_E2 slot will be unavailable when installing M.2 SSD in the M2_4 slot.

Source: https://download.msi.com/archive/mnu_exe/mb/MEGZ790GODLIKE.pdf (page 15).

You are ONLY limited if you install a device in PCI_E2 or M2_4 slot. If you don't add anything to those slots, you get x16 speeds in PCI_E1. Please note the board has other (6) M2 slots you can use with throttling the PCI_E1 slot as shown on page 29. In short, the issue you bring up is not a factor here as well.

BrianInEngland · Jan 29, 2023

Dru2 said:
It again, appears you've misunderstood what you're reading....

Source: https://download.msi.com/archive/mnu_exe/mb/MEGZ790GODLIKE.pdf (page 15).

You are ONLY limited if you install a device in PCI_E2 or M2_4 slot. If you don't add anything to those slots, you get x16 speeds in PCI_E1. Please note the board has other (6) M2 slots you can use with throttling the PCI_E1 slot as shown on page 29. In short, the issue you bring up is not a factor here as well.

You just confirmed what I said - the M2_4 slot is the ONLY gen 5 SSD slot, so what I said is correct - you lose 8 of the GPU lanes if you use a gen 5 SSD in that slot.

Dru2 · Jan 29, 2023

This is what I heard (read) you say...

BrianInEngland said:
Out of interest and to compare I've looked at Intel Z790 boards. With every one I've looked at (two 'high end' from both Gigabyte and MSI) I've noticed that using the Gen 5 M.2 drive slot reduces the PCI-E x16 GPU slot to x8 speed.

In none of the boards you mention is this true - you STILL will have x16 speeds depending on what slots you use. And since each board you mentioned has MORE than one M.2 slot, you are NOT relegated to only getting x8 speeds.

Peace

BrianInEngland · Jan 29, 2023

Dru2 said:
This is what I heard (read) you say...

In none of the boards you mention is this true - you STILL will have x16 speeds depending on what slots you use. And since each board you mentioned has MORE than one M.2 slot, you are NOT relegated to only getting x8 speeds.

Peace

But you are if using a GEN 5 SSD, as my original post states. It clearly says in the manuals for the Gigabyte and MSI boards - using the Gen 5 SSD slots will make the x16 slots run at x8. The Gen 4 and gen 3 slots are irrelevant to this thread - it's the gen 5 SSD slots I mentioned in my first post.

You can't run a Gen 5 SSD AND have x16 GPU slot

BrianInEngland · Jan 29, 2023

Gigabyte Z790 Aorus Master - only one Gen 5 slot (M2C_CPU). The x16 slot shares bandwidth and will run at x8 when M2C_CPU is used. Says it in the specs (see pic). None of the other Z790 Gigabyte boards have Gen 5 SSD slots so this issue doesn't apply (except the Xtreme which I've already mentioned)

BrianInEngland · Jan 29, 2023

MSI Z790 MEG ACE - same again - if M2_4 is used the x16 runs at x8. M2_4 is the only Gen 5 slot.

BrianInEngland · Jan 29, 2023

Here we go with the Z790 Asus Extreme, their top-tier board.
PCI slot runs at x16 with only the GPU installed.
PCI slot 1 runs at x8 if slot 2 is used as well
PCI slot 1 runs at x8 if the M2 slot is used AND then the second PCI slot is disabled as well!

Pic is from the user manual for this board. Again M2_1 is the only Gen 5 slot on the board.

It seems that adding one 4-lane M2 drive removes 16 of the available PCI lanes

hdmi · Jan 29, 2023

bobkn said:
Is there a reason that a second PCI-E 5.0 slot that uses the remaining 4 lanes isn't provided?

I am guessing there exist a few million reasons each one of which costs one dollar. lol

BrianInEngland · Jan 29, 2023

As I said in my original post, I'm looking to upgrade so started doing some research. Coming from the AMD X570 I really do like the X670E boards, but I didn't dismiss Intel completely which is why I was looking into the specs of the Z790. I was actually very surprised to find that these chipsets suffer from the PCI limitations. This is a deal-breaker for me so I'll definitely be going X670E.

Had it been the other way round, Intel would get my money so it's not a 'fanboy' thing or any intent to spark a flame war. Regarding the PCI lane allocations facts are facts at the end of the day!

These are the block diagrams for the Aorus X670E boards. Both can run an x16 GPU slot and have two PCI gen 5 SSDs. The Xtreme will only drop to x8 if one of the bottom m2 slots are used (it has four slots).

hdmi · Jan 29, 2023

BrianInEngland said:
Here we go with the Z790 Asus Extreme, their top-tier board.
PCI slot runs at x16 with only the GPU installed.
PCI slot 1 runs at x8 if slot 2 is used as well

AFAIK with the AMD boards, you can't have more than one PCIe G5 slot running at x16 either.

BrianInEngland said:
PCI slot 1 runs at x8 if the M2 slot is used AND then the second PCI slot is disabled as well!

I have no idea where you've read that. AFAIK the 1st PCIe slot can still run at x16 regardless of whether the 1st M.2 slot is in use so, but the 2nd PCIe slot is disabled when the 1st M.2 slot is in use.

BrianInEngland said:
Pic is from the user manual for this board. Again M2_1 is the only Gen 5 slot on the board.

It seems that adding one 4-lane M2 drive removes 16 of the available PCI lanes

As for the two AMD boards from Gigabyte, AFAIK they also lose 16 of the available PCIe lanes when one M.2 G5 slot is in use, but the difference (also AFAIK) is that these boards give you two M.2 G5 slots versus only one for the Asus so, it all boils down to whether you need that extra M.2 G5 slot to play your games. Or whether the other features are more important.

BrianInEngland · Jan 29, 2023

hdmi said:
AFAIK with the AMD boards, you can't have more than one PCIe G5 slot running at x16 either.

I have no idea where you've read that. AFAIK the 1st PCIe slot can still run at x16 regardless of whether the 1st M.2 slot is in use so, but the 2nd PCIe slot is disabled when the 1st M.2 slot is in use.

View attachment 51262

As for the two AMD boards from Gigabyte, AFAIK they also lose 16 of the available PCIe lanes when one M.2 G5 slot is in use, but the difference (also AFAIK) is that these boards give you two M.2 G5 slots versus only one for the Asus so, it all boils down to whether you need that extra M.2 G5 slot to play your games. Or whether the other features are more important.

Both gigabyte AMD boards can run two G5 SSDs and pci x16. It shows that on the block diagram. The manual for the Asus Z790 I've shown clearly shows the three possible slot lanes configurations:

(PCiEX1/PCIEX2/M2_1)
X16/0/0 (one GPU, no M2}
X8/x8/0 (one GPU plus something in the 2nd slot, no M2)
X8/0/x4 (one GPU, 2nd slot empty as it's n/a, M2 slot used)

Looks clear enough to me... The note and the table seem to contradict each other but it definitely says only X8 if the M2 is used