A method and system for flexibly and efficiently assigning channel path identifiers (CHPIDs) used by operating system software in computer systems to identify the communication path to I/O devices via channels. To avoid wasted CHPIDs, which may be limited in number, CHPIDs are assigned only to channels which are installed on and configured to the computer system. The CHPIDs may be re-assigned concurrently with ongoing system operations via a user interface and/or an imported, pre-defined CHPID mapping.