2.2.5 PCIe (Peripheral Component Interconnect Express) - Notes
PCIe is the standard interface for modern adapter cards. It uses point-to-point serial communication, which gives each component a dedicated link.
PCIe Versions and Speeds
| Version | GT/s | GB/s (x1) | GB/s (x16) |
|---|---|---|---|
| PCIe 2 | 5 | 0.984 | 15.754 |
| PCIe 3 | 8 | 0.985 | 15.754 |
| PCIe 4 | 16 | 1.969 | 31.508 |
| PCIe 5 | 32 | 3.938 | 63.015 |
| PCIe 6 | 64 | 7.561 | 128 |
Slot Sizes and Lanes
- Common lane counts are x1, x4, x8, and x16.
- More lanes means a physically longer slot.
- Up-plugging means putting a smaller card into a larger slot, such as an x8 card into an x16 slot. This works but may run at reduced speed.
- Down-plugging means putting a larger card into a smaller slot. This is only possible if the card is not physically obstructed.
- A slot may be physically x16 but only operate at x8, so check motherboard labels such as x16 @ x8.
Compatibility and Power
- All PCIe versions are backward compatible and run at the speed of the slowest component.
- A graphics slot can provide up to 75W through the slot plus another 75W through a PCIe power connector.
- Other PCIe slots can provide up to 25W.
- If multiple PCIe slots share lanes with other components such as M.2 devices or other slots, the available bandwidth per slot is reduced.