The subject invention relates to a expandable modular system for electrically interconnecting any number of printed circuit boards to a composite motherboard. The motherboard serves as a common connection for transmitting signals to all the printed circuit boards. The subject system includes a support module adapted to hold a fixed number of individual printed circuit boards. A motherboard is mounted within each support module and includes connectors to interface with the printed circuit boards. An electrical coupler is provided which is adapted to link the motherboard of one module to the motherboard of another module. In use, the desired number of printed circuit boards are mounted in a sufficient number of support modules. The couplers are used to electrically link the motherboards of each module in series such that the combination of motherboards and couplers define the composite motherboard. Preferably, each support module includes its own power supply and cooling system. Additional printed circuit boards may be added to a computer system merely by interconnecting additional support modules. In one preferred embodiment, the coupler is designed to permit the support modules to be physically separated thereby reducing heat concentrations and permitting greater flexibility in the design of the shape and size of the computer.