Abstract: A modular bus routing system incorporates segments of a plurality of parallel buses in a substrate on which device connectors are strategically located. Each end of each bus segment is coupled to a connector mounted on the substrate and interconnection between bus segments on different substrates is afforded by a flexible cable containing bus conductors of controlled length and electrical characteristics. A plurality of personality cards provide several different types of bus segment interconnection so that different segments can be terminated, or jumpered to other segments on the substrate. By selecting different personality cards, the plurality of bus segments on a given substrate can be configured as a single serially connected bus, two, four or eight buses. The system affords wide flexibility for computer systems using host initiators and mass storage devices to provide a highly configurable computer system using such elements.