availability level (AL)

An availability level (AL) is a characteristic value for the availability of components, computer systems and communication systems.

The availability level is concerned with the effects and impairments that a specific availability level entails in the event of a problem. The classification recognizes the Availability Levels 1 to 4.

At Availability Level 1 (AL1), data integrity is ensured even if other activities are restricted. At AL2, a termination occurs, accompanied by a new logon. At AL3, individual transactions are interrupted but the subscriber remains online, and at AL4 there is no immediate impact on the user. There is no downtime, nor is availability restricted in any way.