Lane division setup for M.2 storage, CPU, and GPU interfaces
Lane division setup for M.2 storage, CPU, and GPU interfaces
Upgrading to a 3900XT CPU next year means more PCIe lanes—20 total, with your GPU needing 16 lanes. If you choose an M.2 drive, the lane distribution might vary depending on the configuration (e.g., 16x/4x or similar). Pairing it with an X570 M.2 slot that has two slots will affect how the lanes are allocated.
Relies on the specific Mobo model you receive. On X570 or B550 systems, the top M.2 port offers additional 4 PCI-E lanes from the CPU. Therefore, combine 16 plus 4. Certain boards might feature the second and third M.2 slots using PCI-E 3.0 from the chipset, or PCI-E 4.0 from the chipset.
Each CPU will include 20 lanes for PCI devices. This means configurations like 16x or 2x8x and 1x4 for an M.2 SSD are possible. The remaining components are assigned by the board manufacturer to handle them according to their design, mainly focusing on the chipset and I/O interfaces.
This depends on your motherboard, but generally it's set up with 16 channels for the GPU and 4 for the main M.2 slot by default. Your BIOS might let you reduce the 16 channels down to 8 and use the remaining 8 in a lower slot; this is especially handy for SLI or Crossfire configurations, though it isn't the only purpose. The second M.2 port (plus other PCIe slots except the top one or the first two if possible) is usually connected to the chipset instead of directly to the CPU. The chipset can offer many additional lanes and functions as a switch or multiplexer for linking them to the processor.
On an x570 it would utilize PCIe Gen 4x4, not Gen 3x4 (provided the SSD can handle Gen 4). Still, based on other components present, you might notice marginally reduced speeds because the chipset combines the Gen4x4 link with the CPU. This won't impact the CPU lanes at all. In real-world scenarios, most systems don’t usually limit their PCIe bandwidth, so it may temporarily slow down during tests, though noticeable performance drops are unlikely in everyday use.
The M.2 speeds in the x570 chipset are only version 3, not version 4. It seems version 4 is a direct connection to the CPU as I recall.