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Inherent Vice: Magnetic Media

The term magnetic media encompasses a variety of materials, including early wire recorders, numerous formats of audiotape and videotape, computer tape, computer hard drives, and computer floppy discs.

The first machines to record sound magnetically were developed around 1900 by Danish inventor Valdemar Poulson. They included the wire recorder (used for office dictation and recording of telephone messages), as well as a machine that recorded onto steel tape. Both technologies were used well into the 20th century, but magnetic tape eventually became the dominant medium. By the early1950s, magnetic tape had been almost universally adopted in radio and commercial sound recording. See the History of Sound Recording Technology Web site for a detailed chronology of the development of sound recordings.

Videotape was developed during the 1950s and quickly became popular. A number of different formats were developed—many of which did not become commercially successful. Magnetic tape has also been used to back-up and store computer data since the 1950s. More recently, magnetic disks in the form of hard drives, 5¼ inch floppy disks, and 3½ inch floppy disks have been used to store data on personal computers.

Structure

All magnetic tape is made up of two layers: a substrate (backing) and a recording layer (a binder containing magnetic particles). When the tape is passed through a recorder, the magnetic particles are permanently aligned within the binder to produce a copy of the sound waves being recorded. See Magnetic Tape Storage and Handling for illustrations of magnetic tape structure.

Magnetic hard disks consist of a metallic base (usually aluminum) coated on both sides with a recording layer similar to that of magnetic tape. Floppy disks and diskettes have a plastic base with a magnetic recording layer on one or both sides. The newer 3½ inch diskettes are enclosed in a rigid plastic protective jacket, while the older 5¼ inch diskette enclosures are more flexible. For both types, a slot in the jacket allows the read/write head to access the disk.