[coleca]

I've always heard that as "scheduled uptime" or "unscheduled outages". When I worked in a mainframe shop, they used to IPL (reboot) the mainframe every Sunday morning. That down time was never considered as part of the SLA.

[kmoser]

Wow, even Windows boxes can run longer than a week without having to be rebooted. I figured a mainframe would be able to last almost indefinitely.

[nikau]

weekly reboots force the business to build their processes around the system being offline at the same time each week.

That way you don't have to try and organize downtime if maintenance is required, you know every sunday morning is available when needed.