Something I've noticed with new Intel motherboards/chipsets

BrianInEngland · Jan 29, 2023

This is the Z790 chipset brief. It supports either 1x16 PCI gen 5 OR 2x8 PCI gen 5 slots - maximum of 16 PCI gen 5 lanes. Any PCI gen 5 M2 slots from the CPU will use the bandwidth of the PCI slots. Note that the 1x4 PCI lanes are gen 4 not gen 5.

Quite a severe limitation if you ask me!

hdmi · Jan 29, 2023

No, with the Asus there's 16 lanes for the GPU, and 4 for the SSD (add an additional 4 for the 2nd SSD on the AMD boards). The 1st PCIe slot CAN cut down your GPU card to x8, but that's only IF it's a PCIe 5.0 card, which the RTX4090 is not.

BrianInEngland · Jan 29, 2023

hdmi said:
No, with the Asus there's 16 lanes for the GPU, and 4 for the SSD (add an additional 4 for the 2nd SSD on the AMD boards). The 1st PCIe slot CAN cut down your GPU card to x8, but that's only IF it's a PCIe 5.0 card, which the RTX4090 is not.

I don't think any of them work like that - a gen 4 GPU will run at gen 4 x8, not gen 4 x16. Even if you put a Gen 3 SSD in the slot you'll still only get x8 on the GPU slot (the board only detects it's occupied, not what gen it is). I guess they're hardwired that way. I'll hold my hands up if I'm wrong on this!

hdmi · Jan 29, 2023

BrianInEngland said:
I don't think any of them work like that - a gen 4 GPU will run at gen 4 x8, not gen 4 x16. Even if you put a Gen 3 SSD in the slot you'll still only get x8 on the GPU slot. I guess they're hardwired that way.

No, each PCIe G5 lane gives you two downstream PCIe 4.0 lanes if the card you have is a PCIe 4.0 card.

BrianInEngland · Jan 29, 2023

hdmi said:
No, with the Asus there's 16 lanes for the GPU, and 4 for the SSD (add an additional 4 for the 2nd SSD on the AMD boards). The 1st PCIe slot CAN cut down your GPU card to x8, but that's only IF it's a PCIe 5.0 card, which the RTX4090 is not.

hdmi said:
No, each PCIe G5 lane gives you two downstream PCIe 4.0 lanes if the card you have is a PCIe 4.0 card.

Someone on Reddit had EXACTLY this issue. Running a gen 4 4090 GPU was only at x8 until he moved the M2 drive to the second slot. So it's not a case of what gen is being used, it's physically wired that way. Asus Z790 board.

https://www.reddit.com/r/buildapc/comments/yr9vim

hdmi · Jan 29, 2023

BrianInEngland said:
Someone on Reddit had EXACTLY this issue. Running a gen 4 4090 GPU was only at x8 until he moved the M2 drive to the second slot. So it's not a case of what gen is being used, it's physically wired that way. Asus Z790 board.

https://www.reddit.com/r/buildapc/comments/yr9vim

Well there's other boards from Asus with a Z790 that don't appear to have this problem. See:

https://www.reddit.com/r/buildapc/comments/yvkpi1

BrianInEngland · Jan 29, 2023

hdmi said:
Well there's other boards from Asus with a Z790 that don't appear to have this problem. See:

https://www.reddit.com/r/buildapc/comments/yvkpi1

That board doesn't have a gen 5 M2 slot so the problem won't arise.

hdmi · Jan 29, 2023

I see. I guess you could always decide to go for the ROG Maxiums Z790 Hero instead of for the ROG Maximus Z790 Extreme then?

https://dlcdnets.asus.com/pub/ASUS/mb/LGA1700/ROG_MAXIMUS_Z790_HERO/E21512_ROG_MAXIMUS_Z790_HERO_UM_V3_WEB.pdf?model=ROG%20MAXIMUS%20Z790%20HERO#0_ROG_MAXIMUS_Z790_HERO_V3_FrontMatter.indd%3A.18167%3A194071

BrianInEngland · Jan 29, 2023

hdmi said:
I see. I guess you could always decide to go for the ROG Maxiums Z790 Hero instead of for the ROG Maximus Z790 Extreme then?

https://dlcdnets.asus.com/pub/ASUS/mb/LGA1700/ROG_MAXIMUS_Z790_HERO/E21512_ROG_MAXIMUS_Z790_HERO_UM_V3_WEB.pdf?model=ROG%20MAXIMUS%20Z790%20HERO#0_ROG_MAXIMUS_Z790_HERO_V3_FrontMatter.indd%3A.18167%3A194071

Same problem again. The board's M2 slots are only gen 4, the Hyper M2 cards support Gen 5 but if it's inserted into the gen 5 PCI slot both slots will run at x8.

M2_1 is Gen 4 not Gen 5 so can have x16 GPU with the slot in use. Still no way to run x16 GPU and gen 5 M2 drive as using the expansion card will make the x16 slot x8 only.

BrianInEngland · Jan 29, 2023

I'll conclude this thread now.

As the Z790 can only have a maximum of 16 Gen 5 lanes it's not possible to run a GPU at x16 and use the Gen 5 M2 slot at the same time. As the boards are physically wired for gen 5 even running older gen drives will restrict the GPU lanes to x8. Boards that don't have Gen 5 M2 slots won't have this problem.

Like I said in my first post, it's an either/or situation - GPU at x16 but no Gen 5 M2, or Gen 5 M2 but with GPU at x8

It does pay to look at the specs properly when buying hardware, and definitely read the manuals!

Future proofing wasn't even considered...

hdmi · Jan 29, 2023

BrianInEngland said:
As the Z790 can only have a maximum of 16 Gen 5 lanes

Z790 has 20 Gen 5 output lanes, versus 28 Gen 5 output lanes for X670E. But then you are ignoring other factors such as the fact that both Z690 and Z790 have effectively 8 Gen 4 input lanes, just to name only one example.. so apples and oranges.

BrianInEngland · Jan 29, 2023

hdmi said:
Z790 has 20 Gen 5 output lanes, versus 28 Gen 5 output lanes for X670E. But then you are ignoring other factors such as the fact that both Z690 and Z790 have effectively 8 Gen 4 input lanes, just to name only one example.. so apples and oranges.

Each platform has it's own advantages and disadvantages. Like I said I was utterly shocked that Z790 only supports 16 Gen 5 PCI lanes so it sort of limits the usefulness. Intel memory can clock higher than AMD.

hdmi · Jan 29, 2023

BrianInEngland said:
Each platform has it's own advantages and disadvantages. Like I said I was utterly shocked that Z790 only supports 16 Gen 5 PCI lanes so it sort of limits the usefulness. Intel memory can clock higher than AMD.

I am utterly shocked about a lot of things TBH. For example, if I can assume that the main goal is to play demanding games on high settings, then things like P2W, boring DLC and relentless cheating/laming in online multiplayer limits the usefulness to somewhere deep below zero for me so, I quit gaming altogether, like, more than a whole decade ago.

PerpetualCycle · Jan 29, 2023

Puzzled by these two statements.

hdmi said:
Z790 has 20 Gen 5 output lanes, versus 28 Gen 5 output lanes for X670E. But then you are ignoring other factors such as the fact that both Z690 and Z790 have effectively 8 Gen 4 input lanes, just to name only one example.. so apples and oranges.

The z790 chipset doesn't support any Gen 5. It supports 20 Gen 4.

BrianInEngland said:
Each platform has it's own advantages and disadvantages. Like I said I was utterly shocked that Z790 only supports 16 Gen 5 PCI lanes so it sort of limits the usefulness. Intel memory can clock higher than AMD.

The Processor supports 16 Gen5 and 4 Gen4 lanes, not the Z790 chipset.

PerpetualCycle · Jan 29, 2023

BrianInEngland said:
I'll conclude this thread now.

As the Z790 can only have a maximum of 16 Gen 5 lanes it's not possible to run a GPU at x16 and use the Gen 5 M2 slot at the same time. As the boards are physically wired for gen 5 even running older gen drives will restrict the GPU lanes to x8. Boards that don't have Gen 5 M2 slots won't have this problem.

Like I said in my first post, it's an either/or situation - GPU at x16 but no Gen 5 M2, or Gen 5 M2 but with GPU at x8

It does pay to look at the specs properly when buying hardware, and definitely read the manuals!

Future proofing wasn't even considered...

It is the processor that has the 16 Gen5 lanes (+ 4 Gen4). The chipset supports 20 Gen4 lanes. The boards are usually configured with a single Gen5 m.2 that runs off the processor Gen5 lanes, and several m.2 off the Z790 chipset Gen4. If you use the Gen5 m.2 slot, your graphics PCI-e will drop down from 16 lanes to 8. You can however use any of the Z790 Gen4 m.2 slots - they will not impact the graphics PCI-e, it will still be 16 lane Gen5.

BrianInEngland · Jan 30, 2023

geneo said:
Puzzled by these two statements.

The z790 chipset doesn't support any Gen 5. It supports 20 Gen 4.

The Processor supports 16 Gen5 and 4 Gen4 lanes, not the Z790 chipset.

Yes I understand that, but at the end of the day the Z790 boards have a serious hardware limitation. Is there any reason why the CPUs can't use 20 gen 5 lanes?

PerpetualCycle · Jan 30, 2023

BrianInEngland said:
Yes I understand that, but at the end of the day the Z790 boards have a serious hardware limitation. Is there any reason why the CPUs can't use 20 gen 5 lanes?

Because they weren't designed to. There are not 20 Gen5, only 16 Gen5 + 4 Gen4 by design. Can't tell you what the design trade-offs were.

hdmi · Jan 30, 2023

geneo said:
Puzzled by these two statements.

The z790 chipset doesn't support any Gen 5. It supports 20 Gen 4.

"Output lanes" is referring to the downstream lanes, 16 Gen 5 + 4 Gen 4 = 20 "Gen 5 output lanes". The "Gen 5" in "Gen 5 output lanes" here is only referring to the fact that these lanes are downstream of the Gen 5 bus that's in the CPU. But anyway. Gen 5 M.2 SSDs require additional cooling, which is why the Asus ROG Crosshair X670E Extreme seems like a better choice compared to the Gigabyte X670E Aorus Xtreme. Meanwhile, this just happened:

NVIDIA GeForce RTX 4090 Ti aka Next-Gen Titan Pictured A Bit More: Quad-Slot Behemoth With The Largest Founders Edition Cooler To Date

NVIDIA's GeForce RTX 4090 Ti graphics card which is also known as the next-gen Titan has been pictured once again.

wccftech.com

bobkn · Jan 30, 2023

hdmi said:
No, each PCIe G5 lane gives you two downstream PCIe 4.0 lanes if the card you have is a PCIe 4.0 card.

While PCI-E 5.0 nominally has twice the bandwidth of PCI-E 4.0, I am unaware that any board has the provision of duplexing X16 PCI-E 5.0 lanes into two X16 PCI-E 4.0 ones. (That's a pity, as there are no PCI-E 5.0 graphics cards at this time, AFAIK. The highest end ones are still Gen 4.)

If I use an M.2 drive in M.2_1 of my Asus RoG Strix Z690-E, the lanes available got the graphics slot fall back to X8, regardless of the PCI-E generation of the M.2 drive.

Asus makes boards which use the CPU's Gen 4 lanes for the M.2 slot. The graphics slot gets X16 regardless whether the CPU M.2 slot is populated or not.

The story is the same for Z690 and Z790 boards.

hdmi · Jan 30, 2023

bobkn said:
While PCI-E 5.0 nominally has twice the bandwidth of PCI-E 4.0, I am unaware that any board has the provision of duplexing X16 PCI-E 5.0 lanes into two X16 PCI-E 4.0 ones. (That's a pity, as there are no PCI-E 5.0 graphics cards at this time, AFAIK. The highest end ones are still Gen 4.)

If I use an M.2 drive in M.2_1 of my Asus RoG Strix Z690-E, the lanes available got the graphics slot fall back to X8, regardless of the PCI-E generation of the M.2 drive.

Asus makes boards which use the CPU's Gen 4 lanes for the M.2 slot. The graphics slot gets X16 regardless whether the CPU M.2 slot is populated or not.

The story is the same for Z690 and Z790 boards.

Have you verified that the PCIe bandwidth drops to PCIe Gen 4 x8 speed by running the PCIe bandwidth benchmark of 3DMark? Also, in GPU-Z when you run the little benchmark test from the window that opens after you click on the question mark button next to Bus Information, what does the Bus Information say?

Something I've noticed with new Intel motherboards/chipsets

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