A Look at Magnetic Storage

When presented with the term “magnetic storage”, you will probably think of a floppy disk. While floppy disks are a form of magnetic storage, they are not the only form. Perhaps the most common forms of magnetic storage today are hard disk drives and magnetic stripes on credit cards.

Two 3.5

Two 3.5″ high-density floppy disk (front and back) with adhesives (Attr: Victor Korniyenko)

The idea of recording data magnetically was first conceived by Oberlin Smith in 1877. For ten months, he started development on a reel-to-reel system that used a magnetized wire to record sounds. Having no time to develop it further, he placed it in the public domain.

History of Magnetic Storage

Recording data using a magnetic medium was first demonstrated by Valdemar Poulsen in the 1900 Paris Exposition using his new invention, based on Smith’s work, called the Telegraphone. His telegraphone recorded sound on a length of steel wire: an electromagnet, energized by a battery, magnetized the wire; how much the wire was magnetized depended on the electrical signal produced by the connected microphone. The wire was wrapped around a brass cylinder, which was hand-cranked to wind the length of wire while recording. To play back the recorded sound, the battery was detached and the telegraphone was connected to a telephone receiver.

It was incredible! Previous methods of recording sound physically etched the waveform on to a rotating cylinder. By recording magnetically, Poulsen’s telgraphone had the potential to record sound directly over telephone lines. The telegraphone did not really catch on, but it did show that it was possible to record data by magnetic means.

In the 1920s, Fritz Pfleumer invented the Magnetophon, which used an iron-coated paper tape instead of a steel wire as its recording medium. Using paper instead of wire made editing the recordings much easier. The problem was, the audio quality was terrible. In 1941, Walter Weber accidentally discovered the technique of AC bias; it involved continuously recording an extremely high (but inaudible) frequency wave while recording the desired audio. This technique enhanced the quality greatly.

Here is a video that summarizes this milestone quite nicely:

As time progressed, data on magnetic tape became denser and storage devices became smaller. By the 1960s, the familiar compact audio cassettes were in wide use with consumers; by the 1970s, video cassettes. Telephone answering machines also used magnetic tape. The tape that these devices used were no longer paper, but plastic; they were still coated with a layer of iron, sometimes mixed with other substances.

Audio cassettes

“A photograph showing three types of compact audio cassette. Clockwise from top: Metal (Position IV), Chrome (Position II) and Normal (Position I).” (Attrib: Malcolm Tyrrell)

Magnetic disks slowly started replacing magnetic tape in scientific and business applications in 1960. Tapes had a disadvantage over disks: they had to be wound to the desired position. If the read head was at the beginning of the tape and you wanted to access data at the end, you’d have to wait until the tape was wound to the end. With a disk, different areas could be accessed significantly quicker.

Magnetic disks were used for storing data starting around 1962. In the 1970s, 8″ floppy disks emerged. “Floppies” were ideal for use with mini- and microcomputers because they were relatively cheap. They are named floppy disks because they were made of a floppy material, similar to that used in magnetic tape. By the 1980s, floppies shrunk in size from 8″ to 3.5″.

Floppy disk sizes from left to right: 8″, 5.25″, 3.5″.

Hard disk drives had also been developed since its invention in 1956. Unlike floppy disks, hard disk drives had read/write heads in the drive itself, and multiple disks made of aluminum or glass (coated with magnetic material, of course) were stacked to make a cylinder. Again, with time, storage capacity increased and physical size decreased.

Today, these forms of magnetic storage, with the exception of the hard disk, are largely obsolete.

Next section: How Magnetic Storage Works

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