Open Reel Audiotape

Open Reel Audiotape is magnetic tape for audio recording which comes on reels which need to be mounted by hand on a tape player/recorder, rather than being encapsulated in a cassette. A number of different formats have been used, with different numbers of tracks and different speeds, monaural or stereo. A difference in stereo formats is whether the two audio tracks are synchronized side-by-side (to be read by two parallel heads) or slightly out of sync because the heads are adjacent lengthways and one is pointing at a spot on the tape further down than the other.

Links

 * Video discussing the various reel-to-reel audio tape formats