(Audio Video drive) In the late 1990s, an AV drive was a hard disk drive optimized for audio and video applications, which required long, sustained transfers of music and video tracks. AV drives were designed to postpone thermal recalibration so that writing to the disk would not be interrupted while periodic recalibration took place. Today, hard disks use servo calibration to monitor head alignment and have large memory buffers, which together adequately support real-time audio and video transfer. See underrun and thermal recalibration.