A data processing assembly includes one or more hosts connected to one or more I/O Expansion Drawers. Assignment state information is stored on the Expansion Drawer to convey the assignment state of Expansion Drawer(s) resources to the hosts. The host retrieves the assignment state and, from it, determines, for each Expansion Buss cable connected to the host, the number of Expansion Cards in the Expansion Drawer to configure. A change in the number of Expansion Cards in the expansion apparatus may necessitate a change in the assignment state, which can be electronically accommodated (as opposed to a manual reconfiguration). Similarly, a failure of an Expansion Buss cable is addressed by electronically reassigning resources to another host or to the same host over a different Expansion Buss cable without the need for further manual intervention. The assembly is capable of verifying correct cable connection between a host and the Expansion Drawer.