A finite state machine (FSM) for a redundant array of independent disk includes a single process context that maintains an entire finite state required for input/output operations performed in a RAID system. The finite state is only updated in response to calls and call-backs. The call-backs can include procedure returns and interrupt signals. The call is received directly from an application program, and the call-backs are received from a driver and passed back directly to the application software by the finite state machine.