AM5 board supports PCIe Gen 4x16 and Gen 3x8 expansion slots.
AM5 board supports PCIe Gen 4x16 and Gen 3x8 expansion slots.
Hey, after spending some time browsing and using various filters on shopping sites, I'm trying to pick a mainboard that matches my needs: AM5 socket for the 9800X3D, PCIe 4x16 for the RTX 3060Ti (planned upgrade to 4080 later), PCIe 3x8 for my 40G NIC (CX353A ConnectX-3), M.2 NVMe Gen 3 for Crucial P5 1TB, M.2 NVMe for future storage (games, apps, etc.), USB 5Gbps for the Quest 3. I'm open to trade-offs, like skipping a second NVMe slot, but want the NIC to run fast and not get limited by PCIe bandwidth, especially with Resizable Bar. Any suggestions or feedback on setup improvements would be great!
this motherboard fits well in an x16 case. the p5 plus is compatible with gen 4, while this model supports gen 3, 4, and 5 M.2 slots. it lacks built-in wifi, so you'll need an external ethernet connection or a wifi card/dongle.
Offhand (this often happens) I’m not aware of any widely used AM5 boards supporting both an x16 and an x8 slot simultaneously. Ideally you’d stick to x8/x8 configurations. Still, a 4080 in an x8 Gen4 slot works fine. (Check the tabs at the bottom and scroll through the Expansion slots section) https://docs.google.com/spreadsheets/d/1...=755628141 Second PCIe slot only has four lanes electrically.
CPU lanes are typically limited to 8 or 8 lanes only, meaning for a 16 in the main slot you'd need additional lanes elsewhere. Most manufacturers focus on M.2 slots, using a few single-lane options or at most a small 4-lane slot, rather than large expansion slots with many lanes.
Back then the boards used PLX chips to provide extra lanes. Those times are behind us now. We’re getting what we need, but we want more PCIe lanes—often we have to upgrade to something like Threadripper. The M.2 slots on the motherboards feel like a waste of space; it would be better if they came as add-in cards. That way boards would retain more PCIe ports for other purposes, and your M.2 chip would stay cooler rather than sitting at the bottom of your hot GPU.
Thanks, the spreadsheet is really helpful. My main concern is that my 40Gbps NIC only supports PCIe Gen 3, so it really needs around 8 lanes (~8GBps) to avoid throttling (ignoring the possibility of 56Gbps Infiniband). If the GPU works with just x8 at Gen4 or 5, I’ll go ahead with that. Also, last question—can PCIe 4x4 be adapted to PCIe 3x8? I assume such adapters are uncommon and costly; haven’t seen any yet.
Absolutely, adding more than two M.2 slots on even budget mainboards is probably not practical and could limit flexibility and customization options.
These m.2 slots are mostly located beneath the first PCIe port, hidden by the graphics card. To reach them, you’ll have to take the GPU out and remove the M.2 heatsink. When the PCIe M.2 slot is used as an add-in card, it’s positioned directly beside the card—simply unscrew the card and pull it out for access. This method works on older boards but not newer ones.