Abstract: An intelligent backup controller performs graceful shutdown of a processing system upon the loss of main AC power. The power source supply is monitored to detect a switch from main AC power to backup power, triggering a sequence of events effecting the graceful shutdown of the processing system. These events include the steps of notifying the operating system of the processing system to commence shutdown procedures, triggering a first timer beginning with detection of the switch from main AC power to backup power, triggering a second timer upon receipt of a shutdown complete indication from the operating system, and terminating provision at the expiration of either timer unless main AC power is restored during the process. The intelligent backup controller can comprise PC-ISA based printed circuit board having a programmable logic device which serves to effect the monitoring and control functions, along with a serial port emulator for interfacing with the equipment being controlled.