Introduction:

Magnetic recording referring to the storage of data on a magnetized medium is generally classified into two groups of related technologies: media and recording heads. While the first one consists of all technologies concerned with the production and the use of magnetic disks and tapes for storing information, the later one covers all the technologies connected to the process of writing information on the media or reading information from the written media.

Digital recording for storage of computer was first developed by IBM. Magnetic disk drive, called RAMAC, was available in 1957. Earlier to this, magnetic tapes was invented using a paper tape coated either with dried ferromagnetic liquid or with iron powder. Later oxide tapes were developed by 3M Corporation, which ensured the availability of audio recorders in 1940 and video recorders in 1956. On the other hand, the analogue magnetic recording was first demonstrated by a Danish engineer Poulsen by recording acoustical signals on a ferromagnetic wire using an electromagnet connected to a microphone, as shown in Figure 1.1. However, there were two major problems in the recording process: (i) the reproduction of signal was very weak due to the absence of an amplifier, and (ii) low signal to noise ratio due to the nonlinear nature of the recording process.

Magnetic tapes:

Magnetic tapes are the most widely used recording medium for audio and video signals. They are produced as particulate tapes and metal evaporated tapes. The first type is produced in a wide variety of widths at high coating rates and at low cost. However, the major disadvantage of this method is that the magnetic particles only occupy less than 50% of the tape volume. On the other hand, the second type of tapes generally exhibits better performance characteristics but costly to produce. Particulate magnetic recording tapes consist of a coating of magnetic materials with a coating thickness of 3 – 5 m m on a flexible, nonmagnetic substrate, as shown in Figure 1.2.

Figure 1.2: Schematic setup for preparing the magnetic tapes.