PCIe (Peripheral Component Interconnect Express) is a high-speed interface standard for connecting hardware components to a computer's motherboard. It's the primary way that GPUs, fast SSDs, network cards, and other expansion cards communicate with the CPU. The lesson What Is a Bus? explains how data pathways connect computer components, and PCIe is the modern standard for these high-speed connections.
Why it matters
PCIe determines how fast your components can communicate with your system. When you install a graphics card for gaming or AI work, or add an NVMe SSD for faster storage, the PCIe connection is what allows these components to reach their full potential. Understanding PCIe helps you make sense of specifications when building or upgrading a computer.
How PCIe works
PCIe uses "lanes" to transfer data, where each lane is an independent data pathway. Components use different numbers of lanes based on their bandwidth needs:
- x1: 1 lane, used by basic expansion cards (sound cards, simple network cards)
- x4: 4 lanes, used by NVMe SSDs
- x8: 8 lanes, used by some professional cards
- x16: 16 lanes, used by GPUs and high-end devices
More lanes mean more bandwidth. A PCIe 4.0 x16 slot provides about 32 GB/s of bandwidth—enough for the most demanding graphics cards.
PCIe generations
Each new PCIe generation doubles the bandwidth per lane:
- PCIe 3.0: ~1 GB/s per lane (still common)
- PCIe 4.0: ~2 GB/s per lane (current mainstream)
- PCIe 5.0: ~4 GB/s per lane (latest, appearing in new systems)
Newer generations are backward compatible—a PCIe 3.0 card works in a PCIe 5.0 slot (and vice versa), just limited to the slower generation's speed.