A modular computer system formed by connecting a processing module having a processor mounted thereon and a plurality of I/O modules in a stacked form via connectors, where differing ones of the plurality of I/O modules being differing types of I/O modules from one another, which operate with mutually differing types of bus-layout configurations. In accordance with the association of I/O modules with identification information, for each differing type of I/O module stacked via the connectors, said processing module selects from differing preset bus-layout configurations and device drivers from a memory, to dynamically reconfigure the reconfigurable generic bus for accessing the differing type of I/O module.