This paper presents a study of board-level interconnection requirements for highly parallel and massively parallel computing. Analytical models of the I/O bandwidth of popular interconnection networks have been developed and show that current electronic technologies are poor in supporting the necessary I/O density and bandwidth. Optical interconnects appear to offer greater potential in meeting these I/O requirements. Several possible optical implementations of interconnecting a network of electronic processors are compared. The use of polymer waveguides appears to offer the best solution compatible with existing multiboard system architectures.