MAGNETIC STORAGE MEDIA

9/28/2002

Magnetic Storage Media. The first magnetic storage devices were telephone recorders designed around 1900 that recorded audio on moving steel wires or tapes. In the absence of amplifying devices, the recorders performed poorly. By the 1930s practical wire and magnetic tape recorders were in production for dictation and telephone recording. By the 1950s, improvements in magnetic tape recording density and the obnoxious properties of fine steel wire (it snarls and snags) put the magnetic tape into ascendancy. Magnetic disks were also in use, but could not match the recording surface areas that could be presented by magnetic tapes.

Initially, magnetic tapes and disks used iron oxide in a binder on either a rigid or flexible substrate. Later, techniques were developed to (somewhat) control the shape and orientation of magnetizable particles. Eventually media split into "hard" and "soft" media. Hard media require strong fields for recording, but offer high data densities and low drop out rates. "Soft" materials use smaller recording fields, and offer better linearity for intermediate values. Hard materials are used primarily for digital recording, Soft materials are used primarily for analog recording.

Early devices used a variety of magnetic materials including magnetite, Iron carbonyl and Barium ferrite. However, the primary material used has been ferric oxide. Occasionally Iron or Chromium Dioxide are used. Cobalt is sometimes mixed with ferric oxide to improve the coercivity (magnetization density). Small amounts of other metals may be present as a result of processing steps to control crystal shape and orientation. The basic chemistry/physics of recording materials have not changed greatly over the years although the technologies for applying them and controlling the crystal size and orientation have.

Plastic binder and substrate materials are used for tapes or flexible disks. For rigid disks, aluminum or glass substrates are generally used. Media may be rolled on or deposited as a film by plating, evaporation or sputtering.

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