Designing for Ultrahigh Availability: The Unix RTR Operating System

  title={Designing for Ultrahigh Availability: The Unix RTR Operating System},
  author={John J. Wallace and Walter W. Barnes},
Early designers of highly available computers concentrated on recovery from hardware failures to keep downtime to a minimum. But as hardware became more reliable, and systems (particularly software) became more complex, the percentage of downtime caused by hardware decreased. Achieving ultrahigh availability-on the order of a few minutes of downtime per year-requires far more than just reliable hardware. This can be seen from Table 1, which gives causes of downtime for both electronic switching… 

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