A computer system for receiving standard and expanded computer devices includes a chassis, a midplane, and an interposer. The chassis includes bays, each adapted to receive the standard computer device. The midplane includes connectors respectively aligned with the plurality of bays that connect the midplane to a standard computer device disposed within a bay. The standard and expanded computer devices are passed through the interposer, which includes a body defining slots respectively aligned with the bays. Each slot is sized to enable the standard computer device to pass through the slot. The slots includes first and second sets of adjacent slots. The interposer is configured to allow the expanded computer device to simultaneously pass through all slots of the first set of adjacent slots and prevent the expanded computer device, while positioned within the second set of adjacent slots, from fixedly engaging the chassis.