Field Guide · hardware

Also known as: PCIe, PCI-E

PCI Express (PCIe) is the high-speed serial expansion standard that connects add-in cards — graphics, storage, networking — to a computer’s chipset and CPU.1

shared parallel bus (old) device device device one set of wires — devices contend for bandwidth PCI Express — point-to-point root / switch GPU SSD NIC x16x4x1
The old parallel bus wired every device to one shared set of lines, so they competed for bandwidth. PCIe instead gives each device its own point-to-point link to a switch or the CPU's root complex, built from 1, 4, or 16 lanes (x1/x4/x16). Adding a card no longer slows the others.

Overview

PCIe replaced older shared parallel buses with scalable point-to-point links built from one or more lanes, each a pair of differential wires in each direction. A slot is described by its lane count — x1, x4, x8, x16 — and each new generation roughly doubles per-lane bandwidth. Unlike a classic system bus, devices do not share one set of wires; each gets a dedicated link to a switch, so adding cards does not slow the others.

What it’s for

A GPU typically takes a x16 slot, while NVMe SSDs, network cards, and capture cards use narrower links. The slots and lanes live on the motherboard, routed through the chipset. In a high-throughput SDR rig, a PCIe slot is where you would add a fast capture card or an accelerator to feed wideband samples into the decode pipeline without starving the bus.

Sources

  1. PCI Express — Wikipedia, on the PCIe serial expansion standard, lanes, and generations. ↩

See also