The 4.0 PCIe slot isn't functioning properly while the 3.0 slot is operating correctly.
The 4.0 PCIe slot isn't functioning properly while the 3.0 slot is operating correctly.
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!
It could be related to the BIOS configuration. Any PCIe v4 slot will automatically switch back to v3 if the signal quality is poor. Or it may revert from v3 to v2, or v2 to v1. The slot only becomes empty when the slowest v1 speed fails. Alternatively, it might look empty because of BIOS settings. Another possibility is insufficient power supply. I mention this since v4 needs more power than v3. You might assume a power issue would cause a full drop, not just low-quality signals.
Are you employing PCIE riser cable?
If yes, it must be approved for PCIE 4.0 functionality.
Otherwise, if you require a riser cable but can't obtain a suitable one, you may override the PCIE slot to operate in PCIE 3.0 mode within the BIOS settings.
Should you not use a PCIE riser cable yet experience problems with a PCIE 4.0 card in a PCIE 4.0 slot, inspect the CPU socket pins. Certain pins that manage the PCIE connection could be damaged or misaligned.
One slot supports PCIE 4.0 x16, while the other accommodates PCIE 3.0 x4. The distinction is substantial.
The second type offers an eightfold reduction in bandwidth compared to the first.
I confirmed everything is fine.
The manual mentions both x16 standards, with one being 4.0 and the other 3.0.
My PSU is 650Watt, which should be sufficient for running a card over a PCIe 4.0 connection.
Thanks!
Expansion Slot
2x PCIe x16 ports
PCI_E1 (Integrated into CPU)
Compatible with PCIe 4.0
PCI_E2 (From B660 chipset)
Supports up to PCIe 3.0 x4
MAG B660 TOMAHAWK WIFI
Powered by Intel 12th Gen Core processors, this device is built with performance-critical features to surpass competitors. Optimized for enhanced speed using Triple M.2 slots, Memory Boost, Premium Thermal Solution, and M.2 Shield Frozr.
www.msi.com
Its physical configuration offers x16 connectivity, however its actual capability is limited to x4, and it relies on the chipset for data transfer, resulting in slower latency and shared bandwidth with other connected devices.
Wouldn't it be nice if things worked perfectly? There are concerns about new components being faulty. Besides the PCIe version, the lane count matters (x16 versus x4). What happens when you insert the card into the 4.0 slot? Do the fans accelerate and then decelerate, remain steady, or fail to start at all? According to the manual, there are some debug LEDs on the top right of your motherboard—any of these illuminate? The VGA LED is the most likely to light up for inspection. It's also a good idea to verify the processor model and power supply type.
I'm not certain, will adjust the post once I get home.
They all light up during the normal boot process as if the PC starts normally but shows nothing.
I have an I5 12400F with an MSI MAG A650BN power supply.
Edit: I haven't updated the BIOS since assembling the build, could that be the issue?
If the chipset matches what you expect, but it might vary based on BIOS configurations, the situation remains consistent—essentially the same issue arises. A signal so poor that it cannot recover.
I also recall a point about USB: both PCIe and USB operate as "hot plug" in most scenarios. They function like "plug-n-play," meaning firmware isn’t needed to inform drivers about available devices, which can communicate directly with hardware and identify its location on the bus. In USB2 and earlier versions, a single controller manages both legacy and faster connections. With USB3+, a dedicated controller handles the specifics.
Most devices emit data when connected, responding to queries about their specifications—helping the system understand whether they support USB3 or USB2. Only a handful of devices, usually cameras or specialized equipment requiring full USB3 functionality, lack this metadata. Such devices either fail to provide it or completely vanish from the USB bus if their signal quality falls short.
PCIe also sends control signals alongside data. These operate at a slower pace and are more reliable even with poor data transmission (often humorously described as "it sucks!"). PCIe behaves similarly to USB3 in this regard. If control signals fail, the device disappears; if metadata is absent or inaccessible, the device also becomes unusable. When I mention PCIe should reduce speeds, it suggests a data quality problem. If a device isn’t meant to supply metadata or if metadata can’t be accessed, its functionality is compromised—especially on Windows platforms.