In the context of ITWissen.info, uptime is the time that a computer or IT system is available and ready for operation.
The opposite of uptime is downtime. Availability can be determined from uptime and downtime. It is calculated from the ratio of uptime to the sum of downtime and uptime and is given as a percentage value. Availability is divided into availability classes up to high availability. High availability is defined as a value of 99.999%.