A few seconds after your starting point in that first video, you can see a loop of tape vibrating back in forth in a rectangular channel. That's a vacuum column

A few seconds after your starting point in that first video, you can see a loop of tape vibrating back in forth in a rectangular channel. That's a vacuum column, with a (mild) vacuum pulling the tape loop to the right. This lets the servomotors that move the tape past the heads start and stop rapidly, while the heavy tape reels can spin up and down more slowly. See how the vibrating loop passes back and forth across a hole in the middle of the column? That's a pressure sensor. As the loop moves across the hole, the pressure in the hole changes, telling the drive whether it's time to reel in or dispense more tape. More info: https://en.wikipedia.org/wiki/9_track_tape https://en.wikipedia.org/wiki/9_track_tape