Five nines

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Five nines, commonly taken to mean "99.999%", may refer to:

  • High availability of services, when the downtime is less than 5.26 minutes per year (This article has a table that shows the conversion from "nines" to the amount of time a system would be unavailable for various periods.)
  • Nine (purity), a 99.999% pure substance
  • German 5.9 inch artillery shells (World War 1)