Abstract: The preferred embodiment of the present invention provides a data analyzer with a modular bus interface that provides increased flexibility over prior art designs. The modular bus interface allows physical layer devices to be easily swapped, allowing a wide variety of link layer and physical layer device combinations to be tested while minimizing system downtime. In the preferred embodiment, the link layer devices are mounted onto an expansion card that includes a releasable connector. Physical layer devices are mounted onto cards that can plug into the releasable connector. The releasable connector provides the electrical and mechanical connection between the link layer device and the physical layer device, and allows different link layer and physical layer devices to be tested together. By including such a modular bus interface, the preferred embodiment data analyzer provides increased flexibility and performance over prior art systems.