Page "Tape drive" Paragraph 10

In early tape drives, non-continuous data transfer was normal and unavoidable-computer processing power and memory available were usually insufficient to provide a constant stream.

So tape drives were typically designed for so called start-stop operation.

Early drives used very large spools, which necessarily had high inertia and did not start and stop moving easily.

To provide high start, stop, and seeking performance, several feet of loose tape was played out and pulled by a suction fan down into two deep open channels on either side of the tape head and capstans.

The long thin loops of tape hanging in these vacuum columns had far less inertia than the two reels and could be rapidly started, stopped and repositioned.

The large reels would occasionally move to take up written tape and play out more blank tape into the vacuum columns.