Abstract: An interconnect system may be used to interconnect node boards and one or more switch boards coupled to a common backplane in a computer system shelf or chassis. The interconnect system may interconnect the node boards and switch board(s) using external signal paths external to the backplane. In one embodiment, the signal paths may be connected to a rear transition module (RTM) that provides conversion between electrical node board signals and optical switch board signals. Of course, many alternatives, variations, and modifications are possible without departing from this embodiment.