What is x1?
In PC hardware, x1 (said "by one") describes a PCI Express link with one lane. A lane is a pair of signal paths, one for sending and one for receiving, so data flows both ways at once. A PCIe x1 slot is the shortest PCIe slot on a motherboard and is often labeled PCIEX1 or PCIE_X1.
Lane counts compared
| Width | Lanes | Typical use |
|---|---|---|
| x1 | 1 | NICs, Wi-Fi cards, sound cards, USB and SATA expansion cards |
| x4 | 4 | NVMe SSDs (including M.2 slots), fast network cards |
| x8 | 8 | Server network cards and RAID controllers |
| x16 | 16 | Graphics cards |
Bandwidth scales with lane count and PCIe generation. One lane carries about 250 MB/s each way on PCIe 1.0, 500 MB/s on 2.0, about 1 GB/s on 3.0, about 2 GB/s on 4.0 and about 4 GB/s on 5.0. Wider links multiply that by their lane count.
Mixing card and slot sizes
- An x1 card fits any longer PCIe slot (x4, x8 or x16) and works normally, with the link running at x1.
- A longer card won't fit a standard x1 slot. Some boards have open-ended x1 slots that let a longer card hang past the end; it then runs at x1 speed.
- Slot size isn't always lane count. A full-length x16 slot may only be wired for x4 or even x1. The manual and the label printed next to the slot tell you.
- Lanes can be shared. On some boards, using a particular x1 slot or M.2 slot disables another slot or port that shares its lanes.
PCIe x1 vs. legacy PCI
Don't confuse a PCIe x1 slot with a legacy PCI slot. PCI slots are much longer, have no x-number label, and don't accept PCIe cards. A PCIe x1 card won't work in a PCI slot either.
For the CompTIA A+ exam
Core 1 (220-1201) objective 3.5 lists PCI and PCIe among the motherboard connector types and covers installing expansion cards such as sound cards, network cards, capture cards and video cards. Know that the number after the x is the lane count, that a smaller PCIe card works in a bigger PCIe slot, and that a video card belongs in an x16 slot while an x1 slot is fine for a NIC or sound card.