Abstract: A device for preventing unintentional loss of data in a computer system as a result of electrical power interruption comprises a standby power supply, a monitor circuit for generating signals when the main power is interrupted and restored and for monitoring the condition of the uninterruptible supply, and an auxiliary memory circuit. The memory circuit includes a large non-volatile or continuously powered memory and a program stored in ROM which takes over control of the computer and is executed by the CPU when a power interruption is signalled by the monitor circuit. The program allows operations already in progress to be completed and then directs a transfer of the computer's operating state and any application programs and operating system from the computer's RAM to the memory circuit's auxiliary memory. When main power is restored, the ROM program directs the CPU to reload the application programs and operating system into the computer's RAM and to restore the state of the CPU.