The Average Access Time (AAT) is the average access time. The specification of the average access time is used for hard disks, optical storage devices and tape drives because the fastest and slowest access times can differ greatly from one another.
For hard disks, the access time depends on the initial position of the read/write head and the position of the storage area. The longer the path for the access arm, the more time is required to access the data, which increases the average access time. For magnetic tapes, the mean access time depends on the location of the magnetic tape just below the magnetic head. The average access times for tape drives are in the range of minutes.