A plug-in feature board (10) for a computer system has special circuitry to permit the board to customise itself to the particular slot into which it is inserted. Computers of the type intended for individual use or use in small networks typically provide insertion slots including connectors to permit feature boards to be added and connected to a bus of the computer for adding new function or capacity. As the computing power of such systems has increased there have been increases in the size of portions of the connecting bus to permit improvements in data transfer performance. In a given computer system there are often two or more bus connector (32) configurations presented in respective slots. By so converting electrical states at selected connector positions as to provide signal information for determining bus configuration for the slot, special logic provided on the board is enabled to determine the characteristics of the slot in which the board is placed and customises the board to respond or limit response in accordance with the requirements for that configuration. By so adapting to the slot the board achieves enhanced applicability and avoids certain system disabling malfunctions which can occur when a board is plugged into a slot for which it is not configured.