In 1898, the Danish telephone engineer, Valdemar Poulsen invented the first   apparatus for magnetic recording known as telegraphone.
Basically, in this apparatus a steel wire was wrapped in a spiral form around a brass cylinder. An electromagnet rotates around the cylinder following the wire in manner proportional to the incoming sound signals. The level of magnetization of the recorded signals in the wire caused a varying voltage in the electromagnet that again was proprotional to the original incoming sound. This apparently simple process of creating a permanent and recoverable magnetic image, proportional to the incoming signal was the basis for all magnetic recording. However, in spite of the simplicity of the Poulsen invention it was still too primitive due to the lack of the valve for the amplification of the signals, as well as a good recording media .In the beginning of the twenties, Oberlim Smith used iron filing as the magnetizing material applied over a flexible backing.
Based in this  pioneering researches,  in 1928, E. Fritz Pfleumer in Germany, invented a process for the manufacturing of the tape recording.  For his working on the development of a practical recording media known as the Blaterphone a patent under the nš 500900  was issued to Pfleumer by the German Patent Office.
However, since in the Pfleumer process the magentic material  was applied on a paper made backing, it was still too brittle to support continuous operation. In this way in 1933 the German company BASF started researches to obtein a more reliable magnetic recording media.
In 1935, the German company AEG Telefunken launched in the market the magnetophone, the foundation of the modern magnetic tape recorder.  This apparatus had an annular magnetic head that through a bias current created the orientation of the magnetic particles in a flexible tape.
However, at the beginning, due to several technological aspects the magnetophone was not economically feasible. In this way, it was only in 1946, just after the II World War, when A.  M. Poniatoff, in the USA, started the first commercial available production line of magnetic tape recorders manufactured under the trade name of AMPEX.
Since then many innovation were introduced in the magnetic recording. Originally the tape recorder used reels with the magnetic tape entailed the drawback of recquiring some skill for handling. In 1965, Philips in Holland launched in the world market the music cassettes, in which the tape is automatically wound in both direction as well it can simply be slid into the tape recorder. Such innovation spread worldwide quickly and in this way it became as much popular as the gramophone.
Around 1970, the quality of the recorded sound on tape was improved even more with the birth of the noise supressors circuits such as the Dolby and DBX as well as the development of new binders and magnetic materials such as the Chromiun Oxide and advanced types of Iron Oxides, allowing great dynamic range with the lowest signal distorsion.

Chronological evolution of the magnetic tape recording

1932 First experiments to produce a reliable magnetic tape recording.
1934 The first magnetic tape recording was introduced in the Berlin, radio exhibition.
1936 London Philharmonic orchestra conducted by Sir Thomaz Beecham recorded the first concert in a magnetic tape.
1940 BASF engineers Braunmühl and Weber improved the magnetic tape dynamic range.
1944 The first magnetic tape recording using hard PVC sheets known as Luvitherm, developed by BASF in Germany.
1950 Worldwide popularization of the magnetic recording.

Photomicrograph of magnetic particles used in a modern music cassette tape recording.


The principle of the magnetic recording showing the operation of the recording and playback heads.
The cross- section of a modern tape recording

Schematical showing the mechanism of transport of a recorder with the respective desmagnetizer heads, writing and reproduction.

Cross-section of a magnetic tape head. Eduard Schüller invented the annular recording head in 1930.

Pictorial evolution of the recording media:
a)Magnetic wire
b)Paper made magnetic tape
c)The first magnetic tape using plastic backing
d)Monophonic magneticc tape
e)Same as (d) but in a three inch format
f) 4 track stereophonic tape recording

Wire tape recorder model 268-1, made by Webster Chicago in the USA circa 1948.
The music cassette tape invented by Philips in 1965.

Illustration of the evolution of the ways of record for magnetic process:

A) Wire or metallic wire magnetizable
B) Magnetic tape using a paper support
C) Magnetic tape using a plastic support
D) Magnetic tape for monophonic reproduction
E) Idem, but with format of 3 inches
F) Stereo magnetic tape with 4 tracks