The PCI Express Base Specification contains the technical details of the architecture, protocol, Link
15 Layer, Physical Layer, and software interface. The PCI Express Base Specification is applicable to all
variants of PCI Express.
The PCI Express Card Electromechanical Specification focuses on information necessary to implementing
an evolutionary strategy with the PCI desktop/server mechanicals as well as electricals. The
mechanical chapters of the specification contain a definition of evolutionary PCI Express card edge
20 connectors while the electrical chapters cover auxiliary signals, power delivery, and the adapter
interconnect electrical budget.