Described are electronics systems and methods for distributing a limited number of lanes of a PCI Express-based processor (CPU) module among a plurality of PCI Express-based I/O modules with which the CPU module is in communication. The CPU module receives a code from each I/O module over a sideband interface between that I/O module and the CPU module. The coded signal represents a link-width capability of the I/O module. The CPU module is configured to allocate a link width to each I/O module based on the fixed number of lanes and the link-width capability as represented by the coded signal received from that I/O module. The link between CPU module and each I/O module is trained in accordance with the link width allocated to that I/O module.