A mechanism is provided for a personal computer to preserve user and system state data in the event of an AC power failure when the computer is in a standby state. When the AC power failure occurs, a switchover circuit connects a rechargeable energy storage medium, such as a rechargeable battery, to the power supply of the computer for powering components of computer, and the computer is awaken. A critical battery alarm is then issued to trigger the operating system of the computer to perform a transition into a hibernation state, during which the state data of the computer are persistently stored. The energy storage medium is disconnected from the power supply after the computer system has entered hibernation.