Methods, systems, and products are disclosed for dynamically allocating communication lanes for a plurality of sockets in a point-to-point, serial I/O expansion subsystem of a computing system, the expansion subsystem including an switch that supports a maximum number of enabled communication lanes, each socket having a same form factor, each socket connected to the switch using a same predefined number of communication lanes, that include: identifying, during a boot process for the computing system, each of the sockets in which an adapter is installed; determining, for each installed adapter, a maximum link width for that adapter; and enabling, for each of the sockets in which an adapter is installed, a set of communication lanes for communications between the adapter installed in that socket and the expansion subsystem switch in dependence upon the maximum link width for each adapter and the maximum number of enabled communication lanes supported by the switch.