ASP.NET Hosting Uptime is a measure of the time a Windows Hosting Server has been “up” and running. It came into use to describe the opposite of downtime, times when a Windows Server was not operational. The uptime and reliability of Windows Server and communications facilities is sometimes measured in nines. “Five nines” means 99.999% availability, which translates to a total downtime of approximately five minutes and fifteen seconds per year.

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It is often used as a measure of Windows Server operating system reliability and stability, in that this time represents the time a Server can be left unattended without crashing, or needing to be rebooted for administrative or maintenance purposes. Conversely, long uptime can indicate negligence, because critical updates can sometimes require reboots.