Glossary · Hardware

PCIe (PCI Express)

PCIe is the high-speed serial bus that connects graphics cards, NVMe drives and other expansion devices to the CPU and chipset.

Updated October 6, 2026

PCIe (PCI Express) is the high-speed serial interconnect used inside computers. Components such as GPUs, NVMe SSDs and network cards connect through lanes that carry data in both directions.

Why it matters

Speed depends on the generation and the number of lanes. Each generation roughly doubles the per-lane bandwidth, and slots are labeled x1, x4, x8 or x16 for lane count.

If a device plugs into a slot with fewer lanes than it wants, it works but may run slower.

You can check the negotiated link in tools such as lspci or the vendor's utility, which show the generation and width actually in use.

Example

PCIe 3.0 x4: about 4 GB/s
PCIe 4.0 x4: about 8 GB/s
PCIe 5.0 x4: about 16 GB/s

A PCIe 4.0 NVMe SSD in a 3.0 slot works but is limited to the lower figure.

Common mistakes

  • Assuming a physical x16 slot always has 16 lanes wired.
  • Putting two NVMe drives on lanes that are shared with other slots.
  • Ignoring that the chipset link can bottleneck several devices.

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