The magnetic tape-recording works on the principle of storing sound signals by magnetizing the ferromagnetic tape in proportion to audio signals. The tape is moved through a magnetic field produced in a small gap of the recording head when audio signals are applied. As a result, the ferromagnetic coating of the tape gets magnetized in proportion to the intensity and polarity of the magnetizing field. The tape moves past the recording head-gap at a uniform speed and presents a clean unrecorded medium across the recording head-gap on which information is recorded instant by instant. During replay, the recorded tape is passed across the replay head-gap at the same speed and direction as used in recording. Some of the magnetic flux lines from the elemental magnets in the tape pass around the laminations of the replay-head as these tiny magnets pass across the gap, because the core of the head provides a low reluctance path as compared to the air gap. Since different sections of tape have different magnetization's, the magnetic field in the core of the replay-head will be continuously changing, causing an induced e.m.f. in the replay-coil wound on the core of the head. This e.m.f. is proportional to the rate of change of flux-linkage and, therefore, gives the audio-signal that has been recorded on the tape.

A magnetic tape-recorder consists of three main parts:
a) Tape transport mechanism commonly known as Tape deck.
b) Record, Replay and Erase heads.
c) Record, Replay amplifier and bias oscillator.