Pci Express Spec

The Peripheral Component Interconnect Express (PCIe) specification has transcended its original role as a mere I/O bus to become the ubiquitous system interconnect fabric for modern computing. This paper examines the PCIe Base Specification from a structural and functional perspective. It analyzes the physical, data link, and transaction layers, detailing packetized data transfer, flow control, and quality of service (QoS) mechanisms. The paper further investigates critical features including Native Hot-Plug, Active State Power Management (ASPM), Single Root I/O Virtualization (SR-IOV), and recent advances in the PCIe 6.0 and 7.0 specifications, such as PAM4 signaling and Flit mode. Finally, the paper discusses integration challenges in heterogeneous computing, including CXL (Compute Express Link) coherency and chiplet-based designs.