A typical 9-track unit consists of a tape transport—essentially all the mechanics that moves tape from reel to reel past the read/write and erase heads—and supporting control and data read/write electronics. The transport typically consists of supply motor, take-up motor, hubs for locking the tape reels in place, a capstan motor (though not necessarily a pinch roller, see below), tape head assembly, miscellaneous rollers which keep the tape in a precise path during operation, and vacuum columns which prevent tape 'snatch'. Data can become corrupted by stretched tape or variations in tape speed, so the transport has to guide the tape through without damaging its edges, move it with minimal wow and flutter, and give it a tension that is low but sufficient to keep the tape in constant contact with the read/write head.