The checkpoint mechanism in KeyKOS

KeyKOS is an object-oriented microkernel operating system. KeyKOS achieves persistence of objects by taking frequent system-wide checkpoints of the entire system state to disk. Checkpoints do not interrupt operation of the system for any significant period of time. On restart from a failure, the entire system is restored to the state at the last checkpoint, and processes resume execution as if there had been no interruption. This single mechanism ensures persistence of all objects over many years, maintains security, and achieves a high degree of fault-tolerance. The checkpointed state can be written to tape for off-site back-up, without stopping the system. A journaling mechanism allows data to be committed between checkpoints. Paging of virtual memory is integrated with the checkpoint mechanism, allowing KeyKOS to achieve extremely high disk I/O performance