Reel to Reel Track Positions

In order to make the best possible use of the storage capacity of a magnetic tape, its width is divided up into two or four tracks. This is known as half or quarter track recording. Halving track width will give double the recording time for the same length of tape.
The division into several tracks has no influence an the frequency response. The dynamic range, however, i.e. the region between the maximum recording level and the tape background noise is reduced. Quarter track recording is also more critical regarding the cleanliness of the heads and the tape.
For mono recording two independent tracks are therefore available with a half track machine, and four with a quarter track machine.
Stereo recording requires a track each for the left and right hand channels. Two tracks are therefore used simultaneously. With half track stereo recording the tape is therefore fully recorded in one go. In the case of quarter track machines only two of the four tracks are recorded when the tape is run through for first time.