Typical availability - five 9s
In service level agreements (SLAs) usually there is a nice number given on availability. No one will guarantee 100% of uptime, but like 99%. Over a year this means quite some downtime. Microsoft claims to aim to keep their systems at 99.999% uptime (except planned downtime). So, during a whole year such a system should not fail for more than about 5 minutes. Sources: Windows Server Administration Fundamentals: Part 4 @ ~0:40 minutes Keywords: Uptime, SLA