PCIe Overview

PCIe is widely used across modern computing systems, powering devices such as SSDs, GPUs, and network interfaces. This article provides a structured overview of PCIe with an emphasis on practical understanding. It covers key concepts including topology, protocol layers, BARs, DMA, and interrupt mechanisms What is PCIe PCIe (Peripheral Component Interconnect Express) is a high-speed serial bus standard used to connect peripheral devices to the main processor. The older PCI bus was parallel—it had 32 or 64 data lines all switching simultaneously. However, parallel buses have a fundamental limitation at high frequencies: signals on different wires arrive at slightly different times (called skew), making it difficult to scale to higher speeds. PCIe uses a high-speed serialized bitstream over differential pairs of wires (called lanes). Each lane consists of one differential pair for transmit and one for receive. Because there are only two wires per direction per lane, PCIe can operate at mu