The specification discloses a structure and related method for determining whether a particular BIOS routine is supported on a computer system, and if so, the service number for that BIOS routine. This determination is made by a software program accessing a table which correlates unique identification numbers for each BIOS routine with a BIOS call service number. The presence or absence of a unique identification number in the table is an indication to the calling program whether the BIOS implements the desired BIOS routine. If the unique identification number exists in the table, it thus identifies the service number for the particular BIOS routine.