Question Gpu pcie 4.0 slot not working while the 3.0 is working

[AjaXI]

Hey good people, I've built my first pc but I've faced a problem. My motherboard has 2 gpu slots, one is gen 4 and the second is gen 3. Both the 4060 and the MSI MAG B660 TOMAHAWK WIFI DDR5 mobo are brand new so they can't be defective. When I put the gpu in the 4th gen slot, nothing is displayed while if I put it in the 3rd gen slot, the pc displays content normally. I know there isn't much of a difference gap between pcie 4.0 and 3.0 but I'm a nerd and I like having and utilizing the very latest technologies. Thank you!

 

[LinuxDevice]

It might be a setting of the BIOS. Any slot capable of PCIe v4 will automatically drop back to v3 speeds if signal quality is an issue. Or revert from v3 to v2, or v2 to v1. It isn't until the slowest v1 speed fails that the slot will appear empty. Or it might appear empty due to BIOS settings. Actually, there is another possibility: Power requirements might not be met. I say this because v4 requires more power to run at the higher speed compared to v3. You might think that if power fails at v4 then it would also revert to v3, but a power failure can cause a complete loss of signal (different than a signal detected of low quality).

Check your BIOS settings. Check if your PSU is marginal, such that v3 would work, but higher speeds might make it insufficient.

 

[SkyNetRising]

Any slot capable of PCIe v4 will automatically drop back to v3 speeds if signal quality is an issue.

It won't.
If board and card are capable of PCIE 4.0, but you have a low quality signal (by using PCIE riser cable not certified for PCIE 4.0 operation) then you get signal failure. There's no auto negotiation to lower PCIE version.

 

[SkyNetRising]

When I put the gpu in the 4th gen slot, nothing is displayed while if I put it in the 3rd gen slot, the pc displays content normally.

Are you using PCIE riser cable?
If yes, then it has to be certified for PCIE 4.0 operation.
Alternatively, if you need to use riser cable and can't get a proper one, then
you can force PCIE slot to PCIE 3.0 operation mode in BIOS.

If you're not using PCIE riser cable, but still get issues with PCIE 4.0 card in PCIE 4.0 slot, then
check cpu socket pins. Some pins responsible for pcie connection might be bent/broken.

I know there isn't much of a difference gap between pcie 4.0 and 3.0 but I'm a nerd and I like having and utilizing the very latest technologies. Thank you!

One slot is PCIE 4.0 x16, the other slot is PCIE 3.0 x4. Difference is very significant.
The other has 8 times less bandwidth than first one.

 

[AjaXI]

Are you using PCIE riser cable?

No I'm not.

then
check cpu socket pins. Some pins responsible for pcie connection might be bent/broken.

Just checked, all good!

One slot is PCIE 4.0 x16, the other slot is PCIE 3.0 x4. Difference is very significant.
The other has 8 times less bandwidth than first one.

On my motherboard's manual it says that they are both x16 excepted one is 4.0 and the other is 3.0.
I also have a 650Watt psu which I think is enough to run a card on a PCIE 4.0 connection.
Also, thank you

 

[kerberos_20]

On my motherboard's manual it says that they are both x16 excepted one is 4.0 and the other is 3.0.

Expansion Slot​

• 2x PCIe x16 slots
  • PCI_E1 (From CPU)
    • Support up to PCIe 4.0
  • PCI_E2 (From B660 chipset)
    • Support up to PCIe 3.0 x4

MAG B660 TOMAHAWK WIFI

Powered by Intel 12th Gen Core processors, the MSI MAG B660 TOMAHAWK WIFI is hardened with performance essential specifications to outlast enemies. Tuned for better performance by Triple M.2 slots, Memory Boost, Premium Thermal Solution, M.2 Shield Frozr,

www.msi.com

it its physicaly x16, but electronicaly its only x4 and its wired through chipset (slow latency and bandwith shared with other devices connected to chipset)

 

[Moonstick2]

oth the 4060 and the MSI MAG B660 TOMAHAWK WIFI DDR5 mobo are brand new so they can't be defective.

Oh, if only that were true. New parts can be defective.

I know there isn't much of a difference gap between pcie 4.0 and 3.0 ...

As above, it's not just the PCIe version but the number of lanes (x16 vs x4).

Does anything happen when you put the card in the 4.0 slot? Do the fans start fast and then slow down, or start fast and stay there, or not start at all?

If you refer to the manual, there are some debug LEDs top right on your motherboard. Do any of these come on? The one labelled VGA is the obvious one to check.

May as well double-check what processor you're using too, and what PSU?

 

[AjaXI]

Does anything happen when you put the card in the 4.0 slot? Do the fans start fast and then slow down, or start fast and stay there, or not start at all?

I'm not sure, will edit the post once I'm home.

If you refer to the manual, there are some debug LEDs top right on your motherboard. Do any of these come on? The one labelled VGA is the obvious one to check.

They all light up in normal boot sequence as if the PC boots normally but displays nothing.

May as well double-check what processor you're using too, and what PSU?

I have the I5 12400F paired with an MSI MAG A650BN psu.
Edit: I also haven't updated the BIOS ever since I put the build together, could that be the problem?

 

[AjaXI]

Hey again good people, posting the fix so future googlers might find it. An update to the latest BIOS update fixed the problem!

 

[LinuxDevice]

It won't.
If board and card are capable of PCIE 4.0, but you have a low quality signal (by using PCIE riser cable not certified for PCIE 4.0 operation) then you get signal failure. There's no auto negotiation to lower PCIE version.

If that's what the chipset is designed for, but I think that depends on the chipset. Or it can depend on BIOS settings. Otherwise what you are describing is the same thing...a signal so bad it cannot fall back.

On the other hand, I am reminded of something in USB. Both PCIe and USB are "hot plug" in most cases. Or, you could say they are "plug-n-play" because firmware is not required to tell drivers what is there, which drivers can talk to the hardware, and where on the bus to find it. In USB2 and older there is a single controller which handles legacy and higher speeds. For USB3+ there is a dedicated USB3 controller. Most devices, when plugged in, generate data in response to a device query. That data is in part to tell the system what its USB3 specs are, and what its USB2 specs are. Only a few such devices lack USB2 metadata, typically cameras or devices which really must run at USB3, or else they will fail; those devices do not provide USB2 metadata. Those devices also will completely disappear from the USB bus if they have a signal quality below that required for USB3.

PCIe has control signals in addition to data. The control runs at a slower speed and is more assured of running even if data signal quality is terrible (the technical terms: "it sucks!" ™️). PCIe is not that different from USB3 in that regard. If the control signals themselves do not succeed, then the device disappears. Or if the metadata is designed to not allow slower speeds, the device would completely disappear. When I say PCIe should back off to slower speeds, it implies that it is a data quality issue. As soon as you talk about a device not intended to provide metadata to run at slower speeds, or when metadata itself is unreachable, this goes out the window (or out of the Windows if we are talking Windows and not Linux 😁).

 

[kerberos_20]

PCIe has control signals in addition to data. The control runs at a slower speed and is more assured of running even if data signal quality is terrible (the technical terms: "it sucks!" ™️). PCIe is not that different from USB3 in that regard. If the control signals themselves do not succeed, then the device disappears. Or if the metadata is designed to not allow slower speeds, the device would completely disappear. When I say PCIe should back off to slower speeds, it implies that it is a data quality issue. As soon as you talk about a device not intended to provide metadata to run at slower speeds, or when metadata itself is unreachable, this goes out the window (or out of the Windows if we are talking Windows and not Linux 😁).

pcie is comparable to network switch rather than USB
there is autonegotiation involved, but thats limited to pcie lanes width (x1/x2/x4/x8/x16)
when theres signal integrity issue, it wont re-try it with different waveform (different PCIe version) - so signal integrity issue at x1 = no device
but since OP mentioned bios update solved it, than there was issue with reading GPU ooprom (vbios)