© A method of operating a data processing system includes the steps of: executing one high level language software program until an instruction is encountered which calls and activity; sensing whether said encountered instruction is linked to the activity which it calls by a first type or a second type depictor; executing another high level language software program for performing the called activity if the sensing step detects the first type depictor; and activating a low level language microcode program or hardware logic circuit for performing the called activity if the sensing step detects the second type depictor.