When the loop of the first two tracks (each song needed two tracks for stereo) had been played, the
playback head of the eight-track machine moved down with a memorable clunking sound to the next two tracks, and so on.
I called the Ampex people and told them that I had ruined the
playback head and needed another head.
They became popular because of their relatively small size, their convenience, and the fact that as they were read by a laser beam rather than being physically touched by a stylus or
playback head, they didn't wear out.
The control track is used to determine playback speed, to maintain proper playback speed even with tape stretching or shrinkage, to ensure that the
playback heads properly read the recorded video tracks, and to update the elapsed time on VCR real-time counters (IEC 1993; IEC 1994; McComb 1995).
They start with a commercially made reel-to-reel tape transport system, then soup it up with customized recording and
playback heads. Their current equipment uses conventional miniature bulk-ferrite construction.
The optical servo is tightly coupled to the drive's recording and
playback heads, allowing for extremely precise positioning of the drive's heads relative to the tape.